TOPRAK KİMYASI DERS NOTLARI II: KISIM

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1 TOPRAK KİMYASI DERS NOTLARI II: KISIM
5. TOPRAK ORGANİK MADDESİ VE YÖNETİMİ PROF.DR. SONAY SÖZÜDOĞRU OK

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3 Türkiye topraklarının çok büyük bir çoğunluğunun
organik madde kapsamı tarımsal üretimden en yüksek verimin alınmasını engelleyecek düzeydedir.

4 Kil ve organik madde miktarının bilinmesi neden önemlidir?
Yüksek KDK değeri (>25) toprağın yüksek kil/organik madde kapsadığının ve fazla miktarda katyon tutubileceğinin en iyi göstergesidir. Düşük KDK değeri (<5) toprağın kumlu ve ve düşük organik madde kapsamında olduğunun ve fazla katyon tutamayacağının iyi bir göstergesidir.

5 5.1. Toprak organik maddesi tanımı, bileşenleri ve kompozisyonu
Organik madde çoğu kaynaklarda humus tanımıyla aynı anlamda kullanılmakla beraber bazı araştırıcılar tamamen değişime uğramış organik materyalleri humus olarak tanımlamaktadır (Çizelge 1).

6 Çizelge 1.Organik maddeye ilişkin tanımlamalar
Terim Tanımlama Toprak Organik maddesi Toprakta canlı biyolojik kütle hariç, ayrışmış ve kısmen ayrışmamış dokuları kapsayan organik bileşikler bütünü Toprak biyolojik kütlesi Yaşayan doku halindeki organik materyal Organik kalıntılar Ayrışmamış bitki ve hayvan dokuları ve bunların kısmen ayrışmış ürünleri Humus Toprakta ayrışmamış ve kısmen ayrışmış dokular ile toprak biyokütlesi dışındaki tüm organik bileşikler toplamı Humik maddeler Yüksek moleküler ağırlıklı, renkli, bu nedenle toprak ve sediment çevresinden ayrılan mikrobiyal ayrışmaya dayanıklı maddeler Humik olmayan maddeler Mikrobiyal ayrışmaya elverişli biyokimyasal olarak tanımlanabilen bileşikler, polisakkaritleri içerirler Humin Humusun alkalide çözünmeyen kısmı Humik asit Koyu renkli alkali ile ekstrakte edilebilen ve asitte çözünmeyen humik maddeler Fulvik asit Renkli, alkali ile ekstrakte olabilen asidifikasyonla humik asidin uzaklaştırılması sonucu çözeltide kalan humik maddeler

7 Elektron mikroskop görüntüleri
Killer yaprakçıklar halinde, kat kat dizili görünüm verir. Elektrik yüklüdürler ve magnet gibi davranırlar, besin maddelerini çekerler ve tutarlar. Humik maddeler Amorf yapıdadırlar Kil mineralleri

8 5.2.Toprak organik maddesinin etkileri
Fiziksel- toprak strüktürünü düzenler,su tutma kapasitesini arttırır, hacim ağırlığını düşürür, koyu rengi ile toprağın sıcaklığını etkiler kimyasal – Yüksek KDK, pH tamponu gibi etki eder,metalleri bağlar,pestisitlerle reaksiyona girerek onları tutar. Biyolojik – toprak organizmalarına enerji sağlar,mikrobiyal popülasyonu ve aktivitelerini arttırır, mikroorganizmalar için besin ve besin deposudur. Toprak organik maddesindeki besinlerin yaklaşık % 1 to 4’ü mikroorganizmaların dönüştürmesiyle bitkilere yarayışlı halde salınır. Bu salınma ılık ve nemli koşullar altında yüksek soğuk ve kuru iklimlerde yavaştır. Mikroorganizmalar bitkiler için besin maddesi salınımı için zorlayıcı kuvvettir.

9 om bitki besin maddeleri için kaynak ve depo,
toprak organizmaları için de enerji kaynağıdır. Toprağın agregasyonunu, havalanmasını, su tutma kapasitesini ve geçirgenliğini olumlu yönde etkiler, erozyonu önler, verimliliğini arttırır. Toprak organik maddesi toprakta pestisit taşınımı, su kalitesi ve evrensel karbon döngüsü üzerinde etkin bir rol oynar. Toprak organik maddesinde ve ayrışan bitki materyalindeki C miktarı canlı biyolojik kütleden 2-3 kez daha fazladır. Toprak organik maddesi dünya yüzeyindeki en büyük karbon rezervini oluşturmaktadır. Dünya topraklarının organik karbon kapsamlarının yaklaşık 1.395x1012 kg olduğu tahmin edilmektedir Toprakta organik maddenin ayrışması atmosfer için en büyük C girdisi kaynağını oluşturmaktadır.

10 Kümeleşme (Flokülasyon ve Agregasyon)
+ Flokülasyon (kimyasal) Agregasyon (organik)

11 Organik Madde Destekli Kümeleşme

12 Çizelge 2. Toprak organik maddesinin genel özellikleri ve toprak özellikleri üzerine etkileri
Gözlemler Toprağa Etkisi Renk Koyu renk Isınmayı kolaylaştırmak Su tutulması Organik madde kendi ağırlığını 20 katı su tutar. Şişme ve büzülmeyi korur. Kil mineralleri ile birleşim Agregat oluşumu sağlar. Gazların değişimine izin verir, strüktürü sabitleştirir, permeabiliteyi artırır. Şelatlama Cu2+, Mn2+, Zn2+ ve diğer polideğerlikli katyonların durağan kompleksler oluşturması Yüksek bitkilere mikrobesinlerin yarayışlılığını artırabilir. Suda çözünürlük Organik maddenin killerle beraberliği nedeniyle organik madde çözünmezdir. Çok az bir organik madde yıkanma ile kaybedilir. Tamponlama eylemi Organik madde zayıf asit, nötral ve alkalin pH’larda tamponlama yapmaktadır. Toprakta uniform bir pH reaksiyonunun devamlılığını sağlar. Katyon değişim Humus mEq100g-1 Toprakların katyon değişim kapasitesini artırabilir. Mineralizasyon CO2, NH4+, NO3-, PO4-, SO42- gibi bileşenlerine ayrışmasıdır. Bitki gelişimi için besin elementlerinin bir kaynağıdır. Organik moleküllerle birleşimi Pestisitlerin parçalanması, devamlılığı, biyoaktivitesini etkiler. Kalıcı kontrol için pestisitlerin uygulama oranını değiştirir.

13 Artan pH organik maddenin KDK ni artırır Hidrojen Besin maddesi
Düşük pH, 4 - 5 (asidik toprak) Nötr pH, 7

14 Humin maddeler koyu renklidir ve güneş ışınlarını daha iyi absorbe ederler. Böylece toprakların daha çabuk ve iyi ısınmalarını sağlarlar. Organik maddece varsıl topraklar ilkbaharda erken ısınacakları için vejetasyon periyodu da uzamış olur Organik maddenin KDK’sının yüksek oluşu, kapsadıkları karboksil (COOH) ve fenolik hidroksil (OH) guruplarındandır ve topraklarda bbm’nin yıkanarak uzaklaşmalarına engel olur Tarım ilaçlarının adsorpsiyonuna veya deaktivasyonuna yada her ikisinde de etkilidir Bitki besin maddesi kaynağı olarak görev yapar ve bitki besin maddelerinin yarayışlılıklarını artırır.

15 Tarım topraklarında organik maddenin miktarı % 1- 10 arasında değişmektedir.
Toprakların organik madde içerikleri birbirinden farklıdır örneğin çöl topraklarında % 0,2’den az, organik topraklarda ise % 80’den fazla organik madde bulunmaktadır. Toprak organik maddesi topraklar için son derece önemli bir kalite faktörüdür.

16 5.3. Bitkilerin dokularında bulunan organik bileşikler
Çizelge 3. Yüksek bitki kalıntılarının bileşiminde bulunan organik maddeler (%) Organik bileşikler Bitki Dokusu (%) Toprak organik maddesi Karbonhidratlar Şekerler ve nişasta Hemiselüloz Selüloz 1-5 10-28 20-50 0-2 2-10 Protein Suda eriyebilen basit ve ham proteinler 1-15 28-35 Lignin 10-30 35-50 Yağlar, mumlar, taninler vb. 1-8 OM bileşiminde oluştuğu ortama göre değişmekle birlikte genel olarak %50 C, %40 oksijen, %5 H, %4 N ve %1 S bulunmaktadır. Bitki besin maddeleri toprağın inorganik fraksiyonuna bağlandığı gibi organik maddeye de değişebilir katyon ve anyonlar halinde veya katyon köprüleri ile bağlanabilir, organomineral oluşumların yüzeylerinde adsorbe edilmiş halde bulunabilir.

17 5.4. Bitkilerin dokularında bulunan bileşenlerin ayrışma hızları
Çizelge 4. Bitki bileşenlerinin ayrışma hızı Ayrışma Şekerler, nişaştalar, proteinler Ham proteinler Hemiselüloz Selüloz Lignin, yağlar ve mumlar Çabuk ayrışır Çok yavaş ayrışır Taze organik materyal toprağa karıştığında hemen bakteri faaliyeti başlar: Şekerler, proteinler ve amino asitler gibi basit şekerlerle beslenmeye başlarlar ve bakteri nüfusu artar. Bakteriler kalıntılardaki bazı kompleks organik bileşikleri parçalayamazlar ve geri kalan materyalden yararlanmaları engellenmiş olur.

18 Lignin suda, çoğu organik çözücüde ve sülfürik asitte çözünmez, mikrobiyal ayrışmaya da son derece dayanıklıdır. Bu özelliklerinden dolayı lignin organik maddenin oluşmasında (özellikle humik madde) önemli bir rol oynar. Basidiomycetes ve Ascomycetesler önemli lignin parçalayıcı organizmalardır. Ligninin biyodegradasyonu sonucu polifenoller ve fenoller oluşur. Ayrışma, organik kalıntıların fiziksel olarak parçalanması, kompleks organik moleküllerin basit organik ve inorganik moleküllere dönüşümüdür.

19 Ayrışma hızını etkileyen üç temel faktör:
toprak organizmaları, fiziksel ortam ve organik maddenin yapısıdır. Toprak organik maddesinin oluşumunda mikrobiyal degradasyon ve polimerizasyon aşamaları sonucunda ortama karbondioksit, enerji, su, bitki besinleri ve yeniden sentezlenmiş organik karbon bileşikleri verilir. Bu olaya humifikasyon denir .Lignin ayrışmasından gelen peptitler, aminoasitler ve aromatik bileşikler anahtar bileşenlerdir ve bunlar hümik materyalleri oluşturur.

20 Şekil 1. Toprak organik maddesinin oluşum aşamaları
Bitki artıkları Basit şekerler ve organik bileşikler Polifenoller Fenoller benzoik asit diğer aromatik bileşikler Peptitler ve aminoasitler Modifiye ligninler Mikrobiyal degradasyon Quinonlar Hümik maddeler Polimerizasyon

21 5.5. Toprakların organik madde (humus) kapsamlarına göre sınıflandırılması
Çizelge 5. Kültür topraklarının kapsadıkları organik karbon ya da organik madde miktarına göre sınıflandırılması Sınıflandırma % organik C % organik madde Az humuslu <1 <2 Orta humuslu 1.1-2 2.1-4 Fazla humuslu 2.1-5 4.1-10 Çok Fazla humuslu >5 >10 % organik madde =% C x 1.72 veya organik maddesi yüksek topraklarda yerine 2 ile çarpılı.

22 5.6. Topraklarımızın organik madde durumu
Çizelge 6. Ülkemiz topraklarının organik madde kapsamlarına göre dağılımı (Eyüpoğlu, 1999) Organik madde Alan (ha) Oransal dağılım (%) Çok az ( <% 1) 21.47 Az (% 1-2) 43.78 Orta (% 2-3) 22.62 İyi (% 3-4) 7.57 Yüksek ( >% 4) 4.55

23 Şekil 2. Toprak gruplarının organik karbon içerikleri

24 Şekil 3.Organik maddenin fraksiyonları
karbonhidrat,protein, amino asit kimyasal organik bileşikler Yavaş ayrışırar Kolayca ayrışır ve kaybolur

25 Şekil 4.Organik maddenin fraksiyonlarına ayrışması
(Alkali ile ekstraksiyon) Çözünebilir (asit ile muamele) Çökelti Humik asit Berrak çözelti Fulvik asit Çözünemeyen Humin

26 Çizelge 7.humik ve fulvik asitlerin özellikleri
Örnek Element analizi (%) C H N S O kül Fülvik asit Hümik asit 49.5 56.4 4.5 5.5 0.8 4.1 0.3 1.1 44.9 32.9 2.4 0.9 Fonksiyonel grup analizi (meq/g) COOH Fenolik-OH Toplam asitlik 9.1 3.3 2.1 12.4 6.6

27 5.7. Organik maddenin yük kaynakları
Fonksiyonel gruplar: COOH and R-OH grupları -COO- K+ NH+ -0- -COO- Ca+2 -0- Na+ H+ Organik madde pH 7.0 KDK cmol/kg

28 Organik Madde - fonksiyonel gruplar: karboksil, hidroksil, fenolik
* Humus, Humik Asit, Fulvik Asit

29 5.8. Organik madde: azot kaynağı
Azotun % 90’nı organik haldedir. Yarayışlı hale gelmesi için mineralize olması gerekir. Amonyum N (NH4+): İnorganik, çözünebilir halde Nitrat (NO3-): İnorganik, çözünebilir halde Atmosferik N (N2): atmosferin % 80’nini oluşturmasına rağmen N-fikse eden bitkiler dışında diğer bitkilere faydalı değildir. Nitrit (NO2-): sadece anaerobik koşullar altında.Bitkiler için toksiktir. Genellikle topraklarda önemli miktarlarda bulunmaz.

30 Mineralizasyona karşı immobilizasyon
Mineralizasyon – organik bağlı bileşiklerin organizma veya bitkilere yarayışlı hale gelmesi Immobilizasyon – inorganik formdaki bir elementin bitkilere yarayışlı olmayan organik forma dönüşmesi

31 Toprak organik maddesi
Şekil 2. Mineralizasyon Bitki artığı Toprak organik maddesi Mikrobiyal biyokütle Mineralizasyon NH4+ NO2- NO3- Oksidasyon N2O N2 Redüksiyon PO4-3 SO4-2 Bitki alımı Tutulma Yıkanma

32 Organik madde dekompozisyonu Karbon ve Azot döngüsü
Degredasyonun her bir döngüsünde organik karbonun yaklaşık 2/3 ü enerji olarak kullanılır ve CO2 olarak salınır Degredasyonun her bir döngüsünde organik karbonun yaklaşık 1/3 ü mikrobiyal hücrelerin yapımında veya toprak organik maddesinin bir parçası haline gelir. CO2 Bitki artığı Degradation of organic material involves in important balance between carbon and nitrogen in the material being degraded, in the degraders, and in the soil. When fresh litter is degraded, about 2/3 of the carbon is released as carbon dioxide, and about 1/3 goes into building new biomass. This cycle repeats over and over until the material is degraded to stable soil humus. CO2 Bakteri, Fungus Toprak organik maddesi Nematodlar protistler, humus

33 5.9. C:N (karbon/azot) oranı
Düşük C:N oranı (<25:1) : mineralizasyonun ve hızlı ayrışma oranının göstergesidir. yüksek C:N oranı (>25:1) immobilizasyonun ve düşük ayrışma oranının göstergesidir. düşük C:N oranı (yüksek N değeri) -sulandırılmamış çiftlik gübresi, otlar, sebze atıkları Orta derede C:N oranı olan materyaller – çoğu kompostlar, yaprak malçları, örtü bitkilerinin artıkları yüksek C:N oranı olan materyaller – saman,ağaç kabuğu,odu parçacıkları, talaş, mısır sapları,

34 Organik madde ayrışması Karbon ve azot oranları
CO2 Organik artık C/N oranı yaklaşık 9:1 Karbonun 2/3 ü CO2 olarak salınır C/N ratio 3:1 Bakteri ve fungusun C/N oranı 8:1 Mikrobial C/N oranı toprağa N salınarak 8:1 de tutulur If the litter has a low C/N ratio, say 9:1, the microorganisms will be taking up material with a C/N ratio near 3:1. This is much more N than they need, and the excess N will be released to the soil as inorganic N in a process called mineralization. Mineralization will usually occur if litter C/N ratio is less than about 20:1. Decomposition of lower C/N ratio materials such as fresh grasses, legumes, and manure tends to be more rapid than high C/N ratio material. Nitrogen will not be a limiting factor and these materials also contain more easily decomposed compounds such as sugars, amino acids and proteins. One thing worth noting here is that once fresh organic materials are converted into soil organic matter, the C/N ratio is going to be relatively low, approaching 8:1. This means that any time soil organic matter is consumed by microorganisms, nitrogen is going to be released providing N for plants. So, soil organic matter is a slow release N fertilizer. Mineralizasyon Toprak N

35 Organik madde ayrışması
C/ N oranı Organik artık C/N oranı yaklaşık 24:1 CO2 C/N oranı 8:1 Karbonun 2/3 ü CO2 olarak salınır Bakteri ve fungusun C/N oranı 8:1 Mikrobiyal C/N oranı N tüketilmeden veya salınmadan sürdürülür Bacteria and fungi have an average C/N ratio in their cells of about 8:1. This ratio must be maintained. If fresh organic material has a C/N ratio of around 24/1, this provides exactly the ratio needed to keep the bacteria and fungi C/N ratio at 8:1. This is because with 2/3 of the carbon being lost as carbon dioxide, the C/N ratio of what the microbes actually use is very close to 8:1.

36 kayıplar artar ve girdiler sabit kalırsa toprak organik maddesi azalır
Dekompozisyon (CO2) Bitki kalıntıları Bitki kökleri Ahır gübresi kompost girdi Toprak om kayıplar But if something happens to disrupt the system, or if management changes significantly, SOM levels can change. For example, if a normally wet soil is drained, decomposition rates could increase substantially. This increases decomposition and the amount of SOM will decrease. Erozyon

37 Girdi artar ve kayıplar aynı kalırsa, toprak organik maddesi artar.
Bitki artıkları Bitki kökleri Ahır gübresi kompost girdiler Toprak organik maddesi Dekompozisyon (CO2) Conversely, if inputs are increased and losses remain constant, SOM levels will increase. Ideally, if we want to increase SOM levels we need to not only increase the inputs, but also decrease the losses. So lets start thinking about how we can do that in a crop production system. kayıplar Erozyon

38 kapsamındaki değişiklik
Toprağın organik madde = İlave organik madde miktarı- Ayrışmış organik madde miktarı kapsamındaki değişiklik Toprak karbonu (C) = KAZANIM KAYIP - Yeşil gübreleme ve örtü bitkileri - korumalı toprak işleme - Bitki artıklarının toprakta bırakılması - Düşük sıcaklık ve gölge - Kontrollü otlatma - yüksek toprak nemi - yüzey malçları - kompost ve çiftlik gübresi kullanımı - uygun azot düzeyleri - yüksek verim - yüksek bitki kök/gövde oranı - Erozyon - Yoğun toprak işleme - Araziden bitki artıklarının bırakılmaması - yüksek sıcaklıklar ve güneşin etkisi - aşırı otlatma - toprak nemi azlığı - yangın - sadece inorganik maddelerin uygulanması - fazla mineral azot -düşük verim -düşük bitki kök/gövde oranı

39 1.Toprak organik madde düzeyini belirleyen faktörler
1.1.Amenajman Neredeyse tüm toprak ve ürün amenajman uygulamaları toprak organik maddesine etki etmektedir Coyne and Thompson (2006) amenajmanın toprak organik maddesi üzerine etkilerini şu şekilde açıklamışlardır: -Kültivasyon toprak organik maddesinin kaybolmasına yardımcı olur. -Illionis Üniversitesi’nin uzun dönemli deneme alanlarında, 125 yılı aşkın sürekli mısır kültivasyonu sonucunda toprak organik maddesi içeriği % 60 daha fazla azalmıştır. -Kültivasyon toprağı havalandırdığı için aerobik ayrışma teşvik edilir. -Toprak işleme agregatları kırarak agregatlarda korunan toprak C’unu mikrobiyal ayrışmaya açık hale getirir. -Drenaj yine toprak organik maddesi üzerine çarpıcı bir etkiye sahiptir. Toprak organik maddesine etki eden uygulamalar toprak işleme ve dikim teknikleri, bitki artıklarının muameleleri, organik artıkların uygulanması, bitki rotasyonu ve ön bitki kullanımıdır .

40 Organik madde miktarının yüksek olması doğrudan üretim miktarını etkilemekten başka ekonomik olarakta katkı sağlar. Örneğin bazı çiftçiler 7 yıllık çiftlik gübresi kullanımı ve korumalı tarım sonrasında toprağın işlenmesi sırasında daha az güç harcandığını ve yakıttan tasarruf edildiğini belirtmişlerdir. Yine bazı araştırıcılar uzun yıllar (8 yıl) çiftlik gübresi uygulanan topraklarda inorganik gübre uygulaması yapılan topraklara göre toprak işleme sırasında kullanılan yakıt tüketiminin azaldığını belirtmişlerdir. Yukarıdaki sonuçlar toprak organik maddesinin artmasının yakıt tasarrufu için bir potansiyel oluşturduğunu göstermektedir.

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46 KATYON DEĞİŞİM KAPASİTESİ
KATYON DEĞİŞİMİ: Kolloid yüzeyinde adsorbe edilmiş olan değişebilir katyonlarla toprak çözeltisi içinde bulunan katyonların yer değiştirmesi Katyon Değişim Kapasitesi: Bir toprağın adsorbe edebileceği değişebilir katyonların toplam miktarıdır. me/ 100 g toprak (Cmol kg -1) 1 miliekivalan, 1 miligram H ile bağlanan yada onun yerine geçen diğer bir iyonun miktarıdır. KDK ‘ si 10 me/100g ise 100g toprak 10mg H veya ona eşdeğer katyon tutmaktadır anlamına gelir.

47 Katyon Değişim Kapasitesi (KDK)
değişebilir katyonlar olarak bilinirler toprak çözeltisinden katyonları çekme – alma kapasitesi (örneğin, kil mineralleri net negatif yüklerinin bir ölçüsüdür) meq/100g biriminde ölçülür (100 g kilin içerdiği net negatif yük) milieşdeğerlik sayısı yüksek değerlikli ve yalın yarı-çapları büyük olan katyonların iyonik yer değiştirme gücü daha fazladır. Al3+ > Ca2+ > Mg2+ >> NH4+ > K+ > H+ > Na+ > Li+

48 Bazla doygunluk yüzdesi: Bir toprağın kolloidal komplekslerinin içerdiği değişebilir bazların ( Ca, Mg, K, Na) katyon değişim kapasitesinin yüzdesi olarak ifade edilen miktarlarına bazlarla doygunluk yüzdesi adı verilir. Miliekivalan değişebilir bazlar / KDK x 100 Bir toprağın bazla doygunluk yüzdesi 80 ise, kolloidin negatif yüklerinin % 80’i bazlar, % 20’si H+ tarafından doyurulmuş demektir. Hidrojenle doygunluk yüzdesi: Bir toprağın kolloidal komplekslerinin içerdiği değişebilir hidrojenin kapasitesinin yüzdesi olarak ifade edilen miktarlarına hidrojenle doygunluk yüzdesi adı verilir. Miliekivalan değişebilir H / KDK x 100 Kurak bölge topraklarının bazla doygunluk yüzdeleri %100 ve pH 8-10

49 Örnek: 1 toprağın KDK: 16 me/100g, değişebilir bazları oluşturan katyon toplamı 12 me/100 g ise bazla doygunluk yüzdesi? 12/16 x 100= % 75 Yani: Toprağın KDK’sinin % 75’ini Ca, Mg, Na, K katyonları ile %25’ini H ve Al iyonları oluşturmaktadır. KDK üzerine; Kil tipi, Kil miktarı, Organik madde miktarı, pH etkilidir.

50 Katyon değişim kapasitesine kolloid tipinin etkisi
Katyon değişim kapasitesine toprak tekstürü ve organik madde miktarının etkisi Kil tipi aynı kalmak koşulu ile toprağın kil yüzdesi arttıkça katyon değişim kapasitesi de artmaktadır. Kumlu olan hafif topraklarda kil kolloidleri ve humus miktarları düşük olduğundan dolayı, killi olan ağır bünyeli topraklara göre katyon değişim kapasiteleri daha düşüktür. Katyon değişim kapasitesine kolloid tipinin etkisi Humus miktarı eşit olmak koşulu ile aynı miktarda kil içeren topraktan montmorillonite sahip olanın katyon değişim kapasitesi, kaolinite sahip olan toprağa göre kat daha fazladır. Buradan anlaşılacağı üzere bir topraktaki kil tipi ve miktarı ile humus miktarı belirlendiğinde, o toprağın katyon değişm kapasitesini tahmin etmek mümkündür.

51 HA=1 olduğunda 1 da arazide 200.000 kg toprak
Problem: HA: 1,15 g/cm3 olan killi bir bir toprağın KDK=10me/100g ise değişebilir H iyonları (tutulabilir) miktarı? Çözüm: HA=1 olduğunda 1 da arazide kg toprak x 1.15= kg toprak var. 1 me H= 1mg H 100 g toprak mg H mg toprak mg H kg toprak kg H tutulabilir

52 1 mg H ile yer değiştirebilmek için 40:2=20 mg Ca (20 mg Ca= 1 me Ca)
Problem: HA: 1,15 g/cm3 olan killi bir toprağın KDK=10me/100g ise değişebilir Ca iyonları (tutulabilir) miktarı? Çözüm: 1 mg H ile yer değiştirebilmek için 40:2=20 mg Ca (20 mg Ca= 1 me Ca) 10 me x 20 mg = 200 mg Ca mg toprak mg Ca kg toprak kg Ca tutulabilir

53 Problem: Eğer 100 g toprak 300 mg Ca tutuyor ise bu toprağın KDK? KDK= 300: 20= 15 me/100g

54 1. toprak 2. toprak KDK=10 me/100g KDK=40 me/100g 8 me Ca 8 me Ca
Hangisinde Ca’un yarayışlılığı (bitkiler tarafından kolayca alımı) daha fazladır? Not: Toprak kolloidleri tarafından adsorbe edilen bir katyonun yarayışlılığı toplam miktarına değil yüzde oranının yüksekliğine bağlıdır.

55 ÇEŞİTLİ MADDELERİN KDK DEĞERLERİ

56

57 Elektriksel çift katman
Toprak Çözeltisi Katyon Konsantrasyonu katyon konsantrasyonuı kil tanesinden uzaklaştıkça azalır + katyonlar kil taneciği Elektriksel çift katman Serbest su

58 Toprakta Kalsyum’un Yarayışlı Hale Getirilmesi
Kolloid yüzeyi Ca + 2H2CO3  H + Ca(HCO3)2 Çözünebilir bikarbonat Adsorbe-edilmiş Ca+2 Adsorbe-edilmiş H+

59 Karşılaştırma Mineral Özgül yüzey (m2/g) KDK (meq/100g) Kaolinit 10-20
3-10 Illit 80-100 20-30 Montmorillonit 800 80-120 Klorit 80

60

61 Organic matter and CEC (cmolcl/kg)
Common %OC for A horizons in productive areas ~4%  So: y = (4.9 * 4%) + 2.4; or CEC = 22 cmolc/kg

62 Rule of thumb for estimation of a soil’s CEC
CEC = (% O.M. x 200) + (% clay x 50) But the CEC of clay minerals ranges from 3 to 150!

63 Calculation of CEC with % clay and % OM
Assume Avg CEC for % OM = 200 meq/100g Assume Avg CEC for % clay = 50 meq/100g CEC = (% OM x 200) + (% Clay x 50) From soil data: soil with 2% OM and 10% Clay 200 x x .1 = = 9 meq/100 g

64 Toprak organik maddesinin sürdürülebilirliği
Before giving this program, add your name and county to the “Prepared by” list in the space below “Department of Crop and Soil Sciences” There are some slide builds included in this program. These are indicated with a bold face “Click” in the text. Managing the soils on your farm so that they can continue to produce high quality crops year after year requires balancing many different operations and inputs to maintain soil quality. Today we are going to talk about one important aspect of soil quality, namely soil organic matter content, and consider how management affects soil organic matter.

65 Organik maddeye neden önem vermeliyiz?
Toprağınız bu şekilde ise Organik maddeye neden önem vermeliyiz? OM toprağın fiziksel özelliklerini iyileştirir Granülasyon ve agregat stabilitesini arttırır. Ağır bünyeli toprakları işlemeyi kolaylaştırır. İnfiltrasyon olayını arttırır Su tutma kapasitesi artırır Erozyonu azaltır Aşağıdaki manzara oluşmaz Well, a little bit of organic matter goes a long way. Most of you likely have heard all this already, but lets review some of the important functions of soil organic matter. SOM improves soil physical properties. It helps to form granules in topsoil and also strengthens and stabilizes the granules so they do not break apart so easily. This helps to lighten and loosen soils, especially heavier textured soils, and makes them easier to work and easier for roots to extend and grow. The improved granulation and structure lets water flow into the soil surface more rapidly. More water enters the soil and can be stored there for plants to use. SOM acts like a sponge and can hold a lot of water. On a weight or a volume basis, SOM can hold much more water than the mineral part of soil can hold. More water entering the soil means less water will be running off the surface. This coupled with stronger soil structure means the soil will be less susceptible to erosion.

66 SOM also has important chemical properties that benefit soil
SOM also has important chemical properties that benefit soil. Cation exchange capacity is a measurement of the capacity of soil to store important plant nutrients such as N, K, Ca, and Mg and supply them to growing plants. Soil organic matter has a very high cation exchange capacity so just a small increase in the amount of SOM can have a big influence on the overall soil cation exchange capacity. Some fertilizers, acid rain, and other soil processes generate acidity in soil and tend to lower soil pH. Organic matter is able to buffer this acidity and help to keep soil pH from decreasing. When soil pH does decrease, the plant availability of Aluminum, Iron, and Manganese increases and these metals can become toxic to plants. Soil organic matter binds strongly to these metals and reduces their toxicity even in acidic soils.

67 Organik maddeye neden önem vermeliyiz???
Besin döngüsü artar Kök uzaması ve bolluğu artar. Besin ve su ilişkileri artar The most important and abundant element in soil organic matter is Carbon, and carbon is energy. In soils, organic matter is food (energy) for the microbes that live there and give the soil life. The bacteria, fungi, actinomycetes and protozoa that live in soil are the organisms that decompose organic matter and also drive nutrient cycling. Humic and fulvic acids (part of SOM) have also been shown to stimulate root elongation and to increase the ability of plant roots to access both water and nutrients. These are just some of the benefits of soil organic matter. Now lets look a little more closely at what soil organic matter is and how it is formed.

68 Toprak organik maddesi nedir?
Bitki artıkları Toprak organik maddesi nedir? Toprakta karbon içeren maddelerin hepsi (karbonat ve bikarbonatlar hariç) Om Bitki artıkları (artık ve kökler) Hayvan kalıntıları ve salgıları Canlı mikroorganizmalar (mikrobiyal biyomas) Zamanla mikroorganizmalar taze organik maddeleri stabil toprak organik maddesine dönüştürür. Bakteri aktinomisetler Fungus Soil organic matter is all the material in soil that is made up of carbon (not including the carbon is in limestone or that is present as carbonates or bicarbonates). So, soil organic matter is all dead plant material, both above ground litter and roots, and all animal remains and excreta. Most scientists also include living soil microorganisms as part of the soil organic matter. These fresh organic materials have none of the properties of soil organic matter that we just mentioned. But over time they are decomposed by soil microbes and gradually turned into soil organic matter. Toprak organik maddesi

69 Organik maddenin parçalanması
Corn leaf pulled into nightcrawler burrow Millepede Ants Soil insects and other arthropods Shred fresh organic material into much smaller particles Allows soil microbes to access all parts of the organic residue The process of degrading fresh organic materials added to the soil is a complex process that involves intricate interplay from many kinds of soil dwelling organisms. Decomposition of complex organic material like plant litter begins with mixing and shredding. Earthworms and other soil arthropods are very adept at this. Earthworms pull litter into their burrows and mix it with soil. Insects and other macro-arthropods feed on the litter pulling it apart into small pieces. Mixing the material into the soil brings it into contact with other soil degraders and greatly increases the surface area exposed to the degraders. In conventional tillage systems this mixing and shredding is done by the farmer. In no-till systems we rely on these critters to do the mixing and shredding.

70 Organic matter decomposition Everyone is involved
Bacteria Population increases rapidly when organic matter is added to soil Quickly degrade simple compounds - sugars, proteins, amino acids Have a harder time degrading cellulose, lignin, starch Cannot get at easily degradable molecules that are protected Bacteria on fungal strands Spiral bacteria When fresh organic material is mixed into the soil, bacteria respond almost immediately. They begin to feed on the simple organic compounds such as sugars, proteins, and amino acids. Bacterial numbers increase very rapidly in response to the food source. But the bacteria have a harder time with some of the more complex organic compounds in the litter, and these complex compounds sometime prevent the bacteria from getting at remaining material they could degrade. Its as if the food is locked in a cupboard. Rod bacteria

71 Organic matter decomposition Everyone is involved
Fungi Grow more slowly and efficiently than bacteria when organic matter is added to soil Able to degrade more complex organic molecules such as hemicellulose, starch, and cellulose. Give other soil microorganisms access to simpler molecules that were protected by cellulose or other complex compounds. Fungus on poplar leaf Tree trunk rotted by fungi So, lets bring on the fungi. Their populations increases more slowly than the bacteria, but they are able to degrade the complex compounds the bacteria could not get at. Things like hemicellulose, starch, and cellulose. The degrading work of the fungi helps to open up the locked cupboard and give other microbes access to the remaining simple compounds. Fairy ring Soil fungus

72 So, lets bring on the fungi
So, lets bring on the fungi. Their populations increases more slowly than the bacteria, but they are able to degrade the complex compounds the bacteria could not get at. Things like hemicellulose, starch, and cellulose. The degrading work of the fungi helps to open up the locked cupboard and give other microbes access to the remaining simple compounds.

73 Fungi and Soil Structure
Fungal hyphae (threads) help hold soil granules together Fungal exudates (goo) help cement soil particles together Another important function soil fungi is the strong influence they have on soil structure. Their hyphal strands help to hold soil aggregates together, and they also excrete organic substances that help cement the aggregates. This is demonstrated in these photos. On the left are soil aggregates in the presence of fungi. These soil aggregates are strong enough to hold up to being shaken in water. On the right is a soil that was similarly aggregated but without fungi. The structure could not stand up to being shaken in water. Active Fungi Present – Soil structure is maintained when immersed in water Fungi absent - Soil structure is not maintained when immersed in water

74 Another important function soil fungi is the strong influence they have on soil structure. Their hyphal strands help to hold soil aggregates together, and they also excrete organic substances that help cement the aggregates. This is demonstrated in these photos. On the left are soil aggregates in the presence of fungi. These soil aggregates are strong enough to hold up to being shaken in water. On the right is a soil that was similarly aggregated but without fungi. The structure could not stand up to being shaken in water.

75 Organic matter decomposition Everyone is involved
Actinomycetes The cleanup crew Become dominant in the final stages of decomposition Attack the highly complex and decay resistant compounds Cellulose Chitin (insect shells) Lignin Waxes Back to decomposition. The final degraders are the actinomycetes. They are the clean-up crew and come in at the final stages of decomposition. Like fungi they are able to degrade complex compounds like cellulose, lignin, and chitin.

76 Back to decomposition. The final degraders are the actinomycetes
Back to decomposition. The final degraders are the actinomycetes. They are the clean-up crew and come in at the final stages of decomposition. Like fungi they are able to degrade complex compounds like cellulose, lignin, and chitin.

77 Organic matter decomposition Everyone is involved
Protists and nematodes, the predators Feed on the primary decomposers (bacteria, fungi, actinomycetes) Release nutrients (nitrogen) contained in the bodies of the primary decomposers Amoeba Bacteria-feeding nematode No to be forgotten are the protists and nematodes. These are the predators, hunting around in the soil for the creatures that got fat from eating the plant litter. They feed on the bacteria and fungi and release nutrients into the soil. Rotifer Predatory nematode

78 Protistler ve nematodlar organik maddenin oluşumundaki rolleri unutulmamalıdır.
These are the predators, hunting around in the soil for the creatures that got fat from eating the plant litter. They feed on the bacteria and fungi and release nutrients into the soil.

79 Degradation of organic material involves in important balance between carbon and nitrogen in the material being degraded, in the degraders, and in the soil. When fresh litter is degraded, about 2/3 of the carbon is released as carbon dioxide, and about 1/3 goes into building new biomass. This cycle repeats over and over until the material is degraded to stable soil humus.

80 Bacteria and fungi have an average C/N ratio in their cells of about 8:1. This ratio must be maintained. If fresh organic material has a C/N ratio of around 24/1, this provides exactly the ratio needed to keep the bacteria and fungi C/N ratio at 8:1. This is because with 2/3 of the carbon being lost as carbon dioxide, the C/N ratio of what the microbes actually use is very close to 8:1.

81 Eğer kalıntılar ın C/N oranı yüksek ise, örneğin 90:1, the microbes will be taking up material with a C/N ratio of 30:1. This is much too high in carbon. They need nitrogen and will scavenge nitrogen from the soil in a process called N immobilization. Because microbes are much better at grabbing nitrogen than plants are, plants become nitrogen deficient. In general, if the litter C/N ratio is above 30:1, immobilization will result.

82 Anız, talaş ve bazı yapraklar gibi yüksek C/N oranı olan materyallerin ayrışması c/N oranı düşük materyallerden daha yavaş ilerler. This is in part because Nitrogen becomes limiting as bacteria and fungi scavenge all the available nitrogen in the soil, and in part because high C/N ratio materials tend to have more of the slowly degraded, complex compounds such as cellulose and lignin.

83 All organic matter in soil is not equal
Scientists describe 3 pools of soil organic matter Organik Materyal CO2 Aktif OM 1 – 2 yıl C/N ratio 15 – 30 Recently deposited organic material Rapid decomposition 10 – 20% of SOM Yavaş OM 15 – 100 yıl C/N ratio 10 – 25 Intermediate age organic material Slow decomposition 10 – 20% of SOM But not all soil organic matter is equal. It is a long, slow process to convert fresh residues or manure into stable soil humus, and scientists have discovered there are different categories of organic matter. The active pool of organic matter is the freshest organic material, plant and animal residues that have just begun to decompose. This is the pool that gives the largest release of nutrients, where decomposition is most rapid and the largest amount of carbon dioxide is released back into the atmosphere. Decomposition of this pool also has the greatest effects on soil structure formation and stabilization. Thus many of the benefits of SOM are from this active or fresh pool – nutrient supply, improved structure, improved water infiltration, decreased erosion, stimulated microbial activity. This is the most dynamic part of the soil organic matter, the pool that undergoes the greatest change and turnover. At the other end of the line is the largest pool of soil organic matter, often called the passive pool. This organic matter is very stable. It has gone through many cycles of decomposition and the molecules that are left here are so complex that microbes have a hard time biting into them or using them as food energy. Scientists have been able to determine that some of this organic matter has been in the soil for as long as 5000 years. The passive organic matter is largely responsible for the increased cation exchange capacity and water holding capacity in soil. In between the active and passive pools of organic matter is the so called slow organic matter. In reality there are not three distinct pools, but rather a continuum of organic materials that ranges from active to passive. The slow organic matter pool has properties that are intermediate between active and passive. It also contributes to cation exchange capacity and water holding capacity. Pasif OM 500 – 5000 yıl C/N ratio 7 – 10 Very stable organic material Extremely slow decomposition 60 – 80% of SOM

84 Toprak organik maddesi basit bir yapı değildir
Toprak organik maddesi basit bir yapı değildir.Taze kalıntıların veya organik gübrelerin stabil humusa dönüşümü uzun ve yavaş bir olaydır. Ve toprak organik maddesinin farklı sınıfları bulunmaktadır. Aktif organik madde havuzu: Henüz ayrışmaya başlamış taze organik materyal, bitki ve hayvan kalıntıları. Bu havuz ayrışmanın en hızlı olduğu besinlerin salındığı ve ve CO in atmosfere salındığı havuzu ifade eder. Bu havuzun ayrımasının toprak strüktürü oluşumu ve stabilizasyon üzerine önemli etkisi vardır.

85 Thus many of the benefits of SOM are from this active or fresh pool – nutrient supply, improved structure, improved water infiltration, decreased erosion, stimulated microbial activity. This is the most dynamic part of the soil organic matter, the pool that undergoes the greatest change and turnover. At the other end of the line is the largest pool of soil organic matter, often called the passive pool. This organic matter is very stable. It has gone through many cycles of decomposition and the molecules that are left here are so complex that microbes have a hard time biting into them or using them as food energy. Scientists have been able to determine that some of this organic matter has been in the soil for as long as 5000 years. The passive organic matter is largely responsible for the increased cation exchange capacity and water holding capacity in soil.

86 There is a constant turnover of organic material in soil.
The quantity of SOM depends on the balance between inputs and losses of organic material Crop Residues Crop Roots Manure Compost Inputs Decomposition (CO2) Soil Organic Matter Clearly soil organic matter is very dynamic, there is a constant turnover of the organic carbon in soils as fresh organic material is added and then decomposed. So, unlike the mineral parts of soil, soil organic matter levels can change depending on inputs and losses. In natural, undisturbed systems such as forests or grasslands, or agricultural soils where management does not change, soil organic matter levels have reached a steady state. That is, over the course of a year or two, the amount of carbon that enters the soil is equal to the amount that is lost from the soil and the SOM level remains constant. It might go up or down a little from one season to the next, but over longer time periods the level is not changing. Losses Erosion

87 Clearly soil organic matter is very dynamic, there is a constant turnover of the organic carbon in soils as fresh organic material is added and then decomposed. So, unlike the mineral parts of soil, soil organic matter levels can change depending on inputs and losses. In natural, undisturbed systems such as forests or grasslands, or agricultural soils where management does not change, soil organic matter levels have reached a steady state.

88 That is, over the course of a year or two, the amount of carbon that enters the soil is equal to the amount that is lost from the soil and the SOM level remains constant. It might go up or down a little from one season to the next, but over longer time periods the level is not changing.

89 If losses increase and inputs remain constant, SOM will decrease
Decomposition (CO2) Bitki kalıntıları Bitki kökleri Ahır gübresi kompost Inputs Soil Organic Matter Losses But if something happens to disrupt the system, or if management changes significantly, SOM levels can change. For example, if a normally wet soil is drained, decomposition rates could increase substantially. This increases decomposition and the amount of SOM will decrease. Erosion

90 But if something happens to disrupt the system, or if management changes significantly, SOM levels can change. For example, if a normally wet soil is drained, decomposition rates could increase substantially. This increases decomposition and the amount of SOM will decrease.

91 Inputs of organic material can also be suddenly decreased
Inputs of organic material can also be suddenly decreased. This is a satellite image of southern Mexico. The bright white material is cloud cover. The thin greyish whispy material is smoke from fires rising high into the atmosphere. These are fires are from forests being cut and burned to clear land for farming. This represents a sudden and huge loss of potential carbon input into the soil.

92 Inputs of organic material can also be suddenly decreased
Inputs of organic material can also be suddenly decreased. This is a satellite image of southern Mexico. The bright white material is cloud cover. The thin greyish whispy material is smoke from fires rising high into the atmosphere. These are fires are from forests being cut and burned to clear land for farming. This represents a sudden and huge loss of potential carbon input into the soil.

93 Ideal olarak om düzeyini arttırmak istiyorsak sadece girdiyi değil kayıpları da azaltmamız gerekir.
Bunu nasıl yapabiliriz?

94 But… SOM will not continue to increase or decrease indefinitely
When inputs or losses are changed, SOM quantity changes to a different level and a new steady state condition is reached. SOM in virgin soil Corn-oats-clover rotation plus manure application Management change imposed SOM level Several long-term studies of soil organic matter levels in production agriculture fields have found that a relatively rapid decrease in SOM occurs during the first 15 – 20 years of cultivation and then the rate of loss slows and reaches a steady state level much lower than in the original soil. For example, the famous Morrow plots at the University of Illinois have been cultivated since 1875. Click With continuous corn production and no fertilizer input, SOM decreased by about 65% from 1875 to 1955 with the greatest loss occurring in the first 20 years. From 1955 until today, SOM levels have remained nearly constant. Plots that were in corn-oats-clover rotations with manure added lost only about 40% of SOM. Beginning in 1955, management changed and NPK fertilizer and lime was added to some continuous corn plots. The resulting increase in corn production also increased and SOM by about 50%. It is important to emphasize that even in though this is a long-term experiment and other long-term experiments show similar results, these time-frames are still too short to see much effect on the Passive organic matter pool. Recall that the age of the passive SOM pool ranges from 500 to 5,000 years. While cultivation and management may have decreased the passive pool a little bit, by far most of the changes have occurred in the active pool and somewhat less in the slow pool. Additions to the passive pool will be minimal in our lifetime. But, this is not bad news. Remember that many of the benefits of SOM – water infiltration, soil structure and stability, and nutrient supply all come from the active pool. Steady state SOM after years of continuous corn cultivation New steady state SOM level 1875 1955 2005 Years of cultivation

95 Several long-term studies of soil organic matter levels in production agriculture fields have found that a relatively rapid decrease in SOM occurs during the first 15 – 20 years of cultivation and then the rate of loss slows and reaches a steady state level much lower than in the original soil. For example, the famous Morrow plots at the University of Illinois have been cultivated since 1875. Click With continuous corn production and no fertilizer input, SOM decreased by about 65% from 1875 to 1955 with the greatest loss occurring in the first 20 years. From 1955 until today, SOM levels have remained nearly constant. Plots that were in corn-oats-clover rotations with manure added lost only about 40% of SOM. Beginning in 1955, management changed and NPK fertilizer and lime was added to some continuous corn plots. The resulting increase in corn production also increased and SOM by about 50%. It is important to emphasize that even in though this is a long-term experiment and other long-term experiments show similar results, these time-frames are still too short to see much effect on the Passive organic matter pool. Recall that the age of the passive SOM pool ranges from 500 to 5,000 years. While cultivation and management may have decreased the passive pool a little bit, by far most of the changes have occurred in the active pool and somewhat less in the slow pool. Additions to the passive pool will be minimal in our lifetime. But, this is not bad news. Remember that many of the benefits of SOM – water infiltration, soil structure and stability, and nutrient supply all come from the active pool.

96 Soil Organic Matter is Dynamic Rate of decomposition is affected by:
1. Environmental Conditions Temperature Moisture Aeration (oxygen) Soil texture Soil pH Soil fertility 2. Quality of added Organic Material C/N ratio Composition/Age Physical properties and placement Fresh vs. “processed” So what factors influence the rate of loss of organic material from soil? These can be divided into Soil Environmental factors and factors related to the Quality of the organic material being added to the soil. We have already discussed the influence of C/N ratios and the composition of plant material. The age at which cover crops are killed and possibly turned under can have a big impact on how quickly they decompose. Fresh, green material will break down much faster than mature, dry material. Physical properties, mainly the size of pieces has a big impact. Compare how long it takes a tree limb to decompose if it lays intact on the soil surface compared to if it is shredded or reduced to sawdust. Compare the difference in decomposition of straw on the soil surface versus straw that has been incorporated by tillage. Some organic materials applied to soils have already undergone some decomposition – these are materials such as composts, manures, and biosolids. Such materials are already similar in many ways to the active soil organic matter pool and their rate of decomposition is slower than fresh material. When it comes to environmental conditions, anything that influences microbial activity in soil will influence decomposition rates. Microbes like to be comfortable. They prefer warm, but not too hot temperatures, sufficient moisture, but not too much. And they love oxygen. Decomposition can happen anaerobically (without oxygen) but it is much slower than aerobic decomposition. In general, conditions that favor good crop growth will also favor decomposition. Also pH ranges and soil fertility levels that favor good crop production will also favor decomposition. Generally coarse textured, sandy soils have less organic matter than heavier, fine textured soils with a lot of clay. This is because sandy soils tend to be better aerated and there is less physical protection of organic matter within soil aggregates. Click So which of these factors can you control? Obviously, you can control the input side of things by altering crop rotations, residue return, and manuring practices. What about the environmental side. Fertility and pH are going to be managed for crop production, and its pretty difficult to change soil texture. We cannot realistically do much about temperature, and if we can manage soil moisture we are going to manage it to supply sufficient water for crops or add drainage to improve crop growth. What about aeration? Can we manage soil aeration? Think about that for a minute. We will come back to it in a few slides. Which of these factors can you control??

97 So what factors influence the rate of loss of organic material from soil? These can be divided into Soil Environmental factors and factors related to the Quality of the organic material being added to the soil. We have already discussed the influence of C/N ratios and the composition of plant material. The age at which cover crops are killed and possibly turned under can have a big impact on how quickly they decompose. Fresh, green material will break down much faster than mature, dry material. Physical properties, mainly the size of pieces has a big impact. Compare how long it takes a tree limb to decompose if it lays intact on the soil surface compared to if it is shredded or reduced to sawdust.

98 Compare the difference in decomposition of straw on the soil surface versus straw that has been incorporated by tillage. Some organic materials applied to soils have already undergone some decomposition – these are materials such as composts, manures, and biosolids. Such materials are already similar in many ways to the active soil organic matter pool and their rate of decomposition is slower than fresh material.

99 When it comes to environmental conditions, anything that influences microbial activity in soil will influence decomposition rates. Microbes like to be comfortable. They prefer warm, but not too hot temperatures, sufficient moisture, but not too much. And they love oxygen. Decomposition can happen anaerobically (without oxygen) but it is much slower than aerobic decomposition. In general, conditions that favor good crop growth will also favor decomposition. Also pH ranges and soil fertility levels that favor good crop production will also favor decomposition.

100 Generally coarse textured, sandy soils have less organic matter than heavier, fine textured soils with a lot of clay. This is because sandy soils tend to be better aerated and there is less physical protection of organic matter within soil aggregates. Click So which of these factors can you control? Obviously, you can control the input side of things by altering crop rotations, residue return, and manuring practices. What about the environmental side. Fertility and pH are going to be managed for crop production, and its pretty difficult to change soil texture. We cannot realistically do much about temperature, and if we can manage soil moisture we are going to manage it to supply sufficient water for crops or add drainage to improve crop growth. What about aeration? Can we manage soil aeration? Think about that for a minute. We will come back to it in a few slides.

101 World SOM levels show influence of temperature and moisture
This map shows where soil organic matter levels are highest and lowest throughout the world. Mostly it shows the influence of temperature and moisture. Desert regions have little plant production because moisture is so limiting, thus there is very little input. They also have high temperatures so when there is some moisture, decomposition is rapid and SOM does not accumulate. We might think the humid tropics would have high SOM levels, after all they are covered by lush rain forests. But SOM levels here are relatively low because soil conditions are warm and moist and ideal for very rapid decomposition. The highest levels occur in cold and wet regions near the arctic or at high mountain elevations. In these regions there is just enough growing season to allow some plant production, but much of the year is cold and greatly slows decomposition. Many soils are also very wet and poorly drained. Limited oxygen also slows decomposition so SOM accumulates. But even if we could control temperature and moisture in our soils to favor SOM accumulation, it would be counter-productive since we would be severely limiting crop production at the same time. So lets focus on things we can do and things that make some sense to do.

102 Diversify crop rotations
What management changes can be made to increase input of organic material? Return more crop residues Add cover crops Diversify crop rotations So, what can we do to increase inputs of organic materials? (try to get some audience response) Click Returning crop residues instead of removing them can double the amount carbon returning to the soil in some production systems. Planting a cover crop in the fall and killing it in the spring can add up to 6,000 lbs of plant material (residue and roots) per acre. Crop rotations, especially those that include hay crops, have been shown to increase soil organic matter. Spreading manure also adds organic material to the soil. The amount added depends on the solid content of the manure being spread. Generally more organic carbon will be added with solid manures than with liquid manures when applying similar amounts of nitrogen. Obviously the amount of manure applied will be limited by either the amount of nitrogen or phosphorus needed. Organic material can also come from off farm sources such as biosolids, fall leaves collected in nearby municipalities, composts, food processing residuals, etc. Each of these materials have their own unique characteristics and care must be taken to be sure they fit into your overall operation and soil management plans. Add other sources of organic material

103 Organik materyallerin girdisini artırmak için ne yapmalıorganic materials?
Returning crop residues instead of removing them can double the amount carbon returning to the soil in some production systems. Click Planting a cover crop in the fall and killing it in the spring can add up to 6,000 lbs of plant material (residue and roots) per acre. Crop rotations, especially those that include hay crops, have been shown to increase soil organic matter. Spreading manure also adds organic material to the soil. The amount added depends on the solid content of the manure being spread. Generally more organic carbon will be added with solid manures than with liquid manures when applying similar amounts of nitrogen. Obviously the amount of manure applied will be limited by either the amount of nitrogen or phosphorus needed.

104 Effects of increased organic material additions on Soil Organic Matter levels
A 30-yr experiment in Connecticut showed returning corn residues increased SOM to 4.6%, compared to 3.4% with no residue returned. A rye cover crop will add about 2,000 lb of C per acre from above ground production and about 500 lb C per acre from roots. After one year about lb of this carbon will likely still be in the soil. An 11-yr study in Vermont showed 20 ton/acre/yr of dairy manure (13% dry matter) was able to maintain SOM levels at 5.2% in conventional tilled corn silage production. 30 ton/acre/yr increased SOM to 5.5%. No manure decreased SOM to 4.3% Just to emphasize the effect of increasing inputs, here are some real numbers. In conventionally tilled corn production, when residues were returned rather than removed, SOM increased by about 35% in 30 years. Cover crops clearly can add a large amount of carbon to soil each year they are grown. The amount of actual increase in soil organic matter of course will depend on how quickly the added carbon is decomposed. Adding dairy manure at the rate of 5,200 lb of dry matter per acre per year maintained soil organic matter levels in conventionally tilled corn, whereas SOM levels decreased by almost 20% in 11 years with no manure addition. But inputs are only half the story. What can you do to decrease losses?

105 What management changes can be made to decrease SOM losses?
Erozyonu azaltır Erozyonu azaltır. Decreasing erosion is one obvious way. Click Of course several things we have just been talking about will help decrease erosion – more crop rotations, more residue left on the surface, and use of cover crops. So adding these to other erosion control measures will certainly help to build organic matter. But our next topic of discussion also has a big impact on erosion. What is another management change that can decrease SOM loss? Reducing tillage is probably the management change that will have the greatest impact on SOM levels. Changing from conventional to minimum or no-till greatly reduces erosion, but it also greatly reduces the rate of organic matter decomposition. Why is this?

106 Toprak işleme organik madde ayrışmasını nasıl etkiler?
Toprak işleme Kalıntıları toprakla karıştıklarında Fiziksel olarak küçük parçacıklara ayrılır Intimate contact between soil and residue Toprağı havalandırır Toprak agregatlarını parçalar organik maddeyi açığa çıkararak ayrımaya maruz kalmasına neden olur. Promotes erosion losses Tillage mixes residues into the soil and in so doing it breaks residues into smaller pieces and puts them into intimate contact with the soil bacteria and fungi that are responsible for decomposition. Decomposition is an aerobic process, and oxidative process that requires oxygen. It is just like burning wood in a stove. You can slow down the process by reducing air flow into the firebox. Open up the dampers and you can burn a lot more a lot faster. Tillage does the same in soil. It mixes air (oxygen) into the soil and greatly speeds up decomposition because oxygen is usually limiting in the soil. Some soil organic matter is protected from decomposition because it is hidden inside soil aggregates and thus is difficult for microbes and air to get at it. Tillage breaks apart soil aggregates and so exposes more organic matter to the agents of decomposition.

107 How much does tillage impact SOM?
The impact is dramatic. Long-term data from 4 Midwestern states shows that in continuous corn and corn-bean rotations moldboard plowing results in an annual loss of 400 lb of organic matter per year, reduced tillage results in a net gain of 200 lb/yr of SOM, and no-till produces a net gain over 1000 lb of SOM each year. But, do not forget about the other environmental factors that influence organic matter levels. The data on this slide come mainly from well-drained fields. Data from more poorly drained fields show that there is not much difference between moldboard plowing and conventional tillage. This is because in poorly drained soils, the extra aeration from tillage is not sufficient to counteract the limited aeration from poor drainage so decomposition is not increased.

108 30 year study in Connecticut Tillage and residue management
After 30 years of continuous corn production in Connecticut, soil carbon levels were higher in No-till than in conventionally tilled plots. These data also show the effect of returning residues, but the effect was only apparent in conventionally tilled plots. In this system most of the corn residue left on the soil surface was apparently decomposed without adding much to the soil carbon level. Corn roots on the other hand appeared to contribute more to SOM under no-till than under conventional till. residue residue residue residue Data from B. Hooker, T. Morris, and Z. Cardon. Department of Ecology and Evolutionary Biology University of Connecticut

109 Distribution of organic matter in soil under conventional and no tillage
One major difference between conventional tillage and no-till systems is in how the soil organic matter is distributed in the profile. In CT systems, crop residues and roots get mixed uniformly through the plow layer so there is very little change in SOM in the upper 15 to 20 cm. In NT systems, crop residues and manures are left on the soil surface and only mixed by worms and other soil macroarthropods. This means that most added organic materials decay near the soil surface and consequently SOM concentrations are greatest at the surface and decrease with depth. There is actually very little difference between the two systems deeper in the profile. Again, most of these increases are in the active SOM pool. This is the pool with highest rates of decomposition and turnover of material. But since this is the pool that has the greatest influence on soil aggregation and stability and water infiltration and ease of root extension, it is actually desirable to have this large active pool located near the soil surface.

110 Managing to Improve Soil Organic Matter Take-home points
Soil Organic Matter is dynamic. The amount of SOM depends on the balance between inputs of organic material and losses of SOM from decomposition and erosion. Both the quantity and quality of organic material inputs can be managed to increase SOM levels. Losses of SOM can be reduced by decreasing erosion and decreasing tillage. Most change in SOM occurs in the active SOM pool. Many soil quality benefits accrue from the active pool. Maintaining the size and rapid turnover in the active pool may be more important for soil quality than actually increasing the overall SOM level. Key points to remember about SOM are: Unlike the static mineral fraction of soil, SOM is dynamic and undergoes constant change and turnover. SOM can be thought of as a reservoir. The level of SOM in the reservoir depends on the rate of additions and the rate of removals. On the input side, SOM can be increased by increasing the quantity of organic material added to soil. SOM can also be increased by adjusting the quality of added organic materials to include some that decompose more slowly. Losses of SOM can be decreased by taking measures to reduce erosion and even more significantly by reducing tillage. Losses and gains of SOM over short time periods (5 – 10 years) occur mostly in the active SOM pool with almost no change in the passive SOM pool. Many of the soil quality benefits attributed to SOM are due to activity in the active SOM pool. For this reason, to obtain the soil quality benefits of SOM maintaining the size of the active SOM pool and a rapid turnover of carbon in this pool may be more important than achieving substantial increases in overall SOM levels.