if plant residues have high TOC (412g/kg), after incorporating into soil, what will effect on soil quality? and does high TOC effect CN ratio? please explain it.
True C:N ratio will change with the increase i n TOC but results of long-term fertilizer experiments with rice-based double or triple cropping systems indicate soil’s capacity to store greater C, and maintain higher C in passive pools and that active fraction of soil C can be used as an indicator of soil health. The inclusion of active pool/ labile SOC is expected to improve the performance of Century eco-system model in predicting SOC changes under different climatic conditions.
Definitely it will change the C:N ratio but the magnitude of C:N ratio will depend on the kind of the organic material added and and its decomposition state.
Definitely affect it. Addition of materials having high TOC relative to N may increase C/N ratio. This leads to rapid increase in population of micro-organisms in the soil. On the other hand, continuous addition of materials having high CN ratio to the soil brings N deficiency.
Mr.Ahmad Ali, interesting question.If one applies organic materials/residues with comparatively low/narrow C:N ratio like legume straws (C:N ratio in the range of 25:1-35:1) they decompose fast as the decomposing microbes get sufficient nitrogen for building their bodies (microbial biomass) from the added organic material itself and some quantity from soil. After exhaustion of the readily decomposable organic material, the microbial biomass will decompose and provide nutrients like N,P and S through mineralization process.The undecomposed ( left over ) organic matter get humified in the soil over time and form part of passive orgnic pool in the soil. When high carbon containing materials like cereal straws (C:N ratio around 70:1) are added to soil ,the decomposition will be slow because of the limitation of nitrogen in the material itself and the soil N is predominantly used ( causing N immobilization).The decomposable part of organic matter in cereal straws is slowly decomposed. As in case of legume straws, the microbial biomass formed is again decomposed and nutrients are released through mineralization.The basic difference is the time taken for decomposition in soil and supply/release of nutrients in both situations.The left over / undecomposed portion of organic matter from straw undergoes humification with time and forms humus/passive pool of soil organic matter.The C:N ratio of the humus/passive pool may not differ in soils amended with low or high C:N ratio materials.But the quantity of humus formed may differ as cereals straws may contain less amount of easily decomposable portion compared to legume straws.The cereals straws probably wth more resistant/undecomposable organic matter may get humified and result in more humic matter/passive pool formation. Only longterm studies may show perceptible differences..But I have not comeacross critical studies with comparison between materials varying in CN ratio on the magnitude of humus formation in soil. It will be interesting if some published papers are located/traced in this line.
I could locate a paper based on long term use of crop rotations with and without legume crop component on quality and quantity of soil organic matter.Mineral fertilizer and manure treatments are superimposed over crop rotations but there is no seperate treatment with legume alone. Cereal straws contain more lignin and legumes one more cellulose and nitrogen In legumes the C:N ratio is narrower compared to other crops and so the mineralization process of legumes residue occurs faster (I have already highlighted in earlier reply).The 32-year long term experiment show that the most important factor which stabilizes carbon content in soil is crop rotation with legumes.This effect has not been obtained even by the systematic application of very high rates of manure. Because of intensified soil microbial activity, the ratio of humic acids to fulvic acids was lower in soil under legumes cultivations compared with manure applications. The UV-VIS spectral analysis of humicacids indicated a high quality of humus of soil under clover with grass mixture. Such studies are needed with comparison between cereal alone and legume alone residue treatments.
http://dx.doi.org/10.5772/53229
Effect of crop rotation and nitrogen fertilization on quality and quantity of soil organic matter. Chapter 9 by Rutkowska A and Pikula D
cdn.intechopen.com/pdfs/41059/In-teffect_of_crop_rotation_and_nitrogen_fertilization_on_the_quality_and_quantity_of_soil_organicmatter
Plants with high lignin contents will have high Carbon /nitrogen content and soil microbes will find it difficult to decompose them ,hence ,they deplete the soil nutrients as source of energy. therefore, plants such as elephant ,guinea grasses and those with high lignin contents should not be used as mulching materials or for addition to soils as fertiliser materials instead use plant materials with low lignin materials such as legumes and others with low C/N ratio as mulching materials and as residues for nutientr supply to soils as well as preventing problems of nutrient immobilization experienced with plants with high lignin contents
It is a good proposition to use the legume residues because of their narrow/low C:N ratio and rapid decomposition in soil.But the supply of legume residues is limited and has alternative uses like fodder/feed. One has to opt for other organic materials for recycling in crop production.When high/wide C:N materials like cereal straws,dry grasses or other materials are applied, the C:N ratio can be lowered by applying fertilizer nitrogen, organic N rich sources like alfalfa pellets, soya meal , poutry/chicken or pig manures depending on availability in the local area or purchasing from the market.Of course one has to provide other conditions like moisture and aeration during decomposition.
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