Effects Of Organic Wastes Incorporation On Soil Organic Carbon And Net Carbon Balance In Wheat-maize Farming System

A large number of agricultural organic wastes are produced in China every year from various agricultural systems. The low utilization of these organic wastes leads to serious potential pollution to the environment. To resolve these problems, five types of organic wastes were applied to a wheat-maize cropping system based on the concept of circular agriculture, including crop straw (CS) representing the inner farmland circulation, pig manure (PM) representing the farming-stockbreeding circulation, biogas residue (BR) representing the farming-biogas circulation, mushroom residue (MR) representing the farming-mushroom circulation, and wine residue (WR) representing farming-processing circulation. The organic wastes were incorporated at an equal rate of carbon. Total organic carbon (TOC) and its components, soil aggregate, and soil greenhouse gases (GHGs) emission were investigated and analyzed to explore the effects of organic waste on soil organic carbon and net carbon balance of the farming system. This experiment began in June2012, data in the period of2012to2013were analyzed in this dissertation. The main results were as follows.(1) Incorporation of the five organic wastes could promote the accumulation of TOC in the wheat-maize intensive farming system, and improve the retention of C in the system. In comparison with CF, TOC was increased by44%on average after three years of organic waste incorporation, the amount of C retention in the system increased4.22-6.30t C ha-1. When compared with the no-fertilization (NF) and fallow (FL), TOC were increased by63%and32%, respectively, and the amount of C retention were increased8.78t C ha-1and6.82t C ha-1. On the whole, the largest positive contribution to the accumulation of TOC was derived from the circular farming mode, and the negative contribution were showed in the acyclic farming mode (CF) and primeval farming mode (NF), whereas a stable TOC was showed in the fallow mode.(2) Among the five orgaic wastes, pig manure, biogas residue and mushroom residue are more benefit to the accumulation of TOC and improvement of C retention. In comparison with CS, the TOC of PM, BR and WR were increased by29%,27%,27%and16%respectively, which indicated that it was more conducive to soil C accumulation by incorporating organic wastes recycling from other systems than crop straw. The amount of C retention in the system raised by1.26tC ha-1,0.761C ha-1,0.261C ha-1in PM, BR and MR when compared to CS.(3) Incorporating organic wastes promotes the formation of soil aggregate, and is beneficial for the protection of TOC, among the organic wastes, PM, BR and MR greatly increase the stability of soil organic C. In comparison with FL, CF and NF, the microaggregate associated TOC and microaggregate-within-macroaggregate associated TOC content were increased by54%,115%and128%in organic wastes treatments. The microaggregate associated TOC and microaggregate-within-macroaggregate associated TOC contents in MR, PM, BR and WR were49%,23%,22%and7%higher than that of CS, which indicated that the returning back of organic wastes from the outside systems were more conducive to the improvement of the TOC stability.(4) Although organic wastes incorporation promote GHGs emissions, it also increases carbon input of farming system, and ultimately presents an enhancement in C retention capacity of the system which served as greenhouse gases "sinks". The soil greenhouse gas warming potential (GWP) of the five organic waste treatments was58%higher than CF, the fact that the net primary production (NPP), system C retention were also improved, could easily offset the promoted GHG emissions, so that the whole system turned out a sink of C, and the net carbon balance (NECB) was increased by264%.The results showed that advantages of C retention and system production can derive from the returning back of organic wastes from the farming-stockbreeding circulation system, the farming-biogas circulation system and the farming-mushroom circulation system. This indicated that it is of great importance to develop circular agriculture, to promote the energy-saving and emissions reduction.