| As a primary factor limiting plant growth and yield, the lack of nitrogen in soil would seriously hamper crop production such as rice and wheat. Circular agriculture, an inevitable alternative for modern agriculture development, is widely considered as an effective means to achieve sustainable use of agricultural resources by planting waste (manure, straw) to replace chemical fertilizer. A reasonable input of nitrogen could increase soil nitrogen supply and improve soil fertility, property as well as its quality, since soil nitrogen mineralization is closely linked to the waste input. There is a vast area of paddy soil in the plain area of Chengdu, most of which are planted in rotation of rice and wheat. However, there are scarce studies on the soil nitrogen supply with rice and wheat rotation cultivation. Therefore, to evaluate the soil nitrogen supply in varied soil with different fertilization practices is of massive significance for the rice and wheat rotation planting system in the Chengdu plain areas. It can also provide guidance on how to implement a more scientific and rational soil management and how to determine a reasonable amount of nitrogen input. Based on field experiment (Tianma town, Dujiangyan) as well as indoor simulation test, the key findings are as follows:Firstly, according to the soil and plant sample test on the five major growth periods of rice and wheat in the field experiment, the manure-straw-inorganic fertilization is the most reasonable mode among the three: pig manure-inorganic fertilizer, straw-inorganic fertilizer, pig manure-straw-inorganic fertilizer. Taking into account of growth indicators in different periods, the final yield and soil nitrogen mineralization, we found that the most favorable mode would be 50% pig manure nitrogen + 50% fertilizer nitrogen + straw (whole amount);Secondly, the time for soil mineralization to reach a steady state is found to be the longest one with the highest cumulative mineralization by an analysis of the differences between nitrogen mineralization with different fertilization and water content in 22? and 30? in the field laboratory simulation in different water and temperature conditions; among the three fertilizations:pig manure-inorganic fertilizer, straw-inorganic fertilizer, pig manure-straw-inorganic fertilizer, the nitrogen accumulation and its mineralization rate is the highest when pig manure and chemical fertilizer are combined;(1) Temperature and moisture are two main influencing factors for soil nitrogen mineralization. The results show that as opposed to flooding condition, aerobic condition (soil moisture is 70% of the field capacity) exhibits a better facilitation to soil nitrogen mineralization at a constant temperature of 30?; at a constant temperature of 22?, soil nitrogen accumulation with low moisture is higher than that with high moisture (the maximum soil moisture is 80%), indicating that exceedingly high moisture will inhibit soil nitrogen minaralization since high moisture might affect microbial activity and affect the mineralized process in turn.(2) At the same culture temperature and moisture condition, the application of organic (pig manure, straw) or inorganic fertilizer would make soil nitrogen mineralization rate and its accumulation amount higher when there is no fertilization. And when N amount of fertilizer alternative for equivalent N amount of pig manure, or with increased amount of pig manure and straw, a significant increase in the cumulative amount of soil mineral nitrogen is revealed;(3) Pig manure as an alternative for nitrogen fertilizer experiment shows:in contrast with the pure use of chemical fertilizers, appropriate amount of pig manure nitrogen fertilizer could accelerate the crop (say wheat and rice) plant height, the aboveground accumulation as well as their production capacity, resulting in increased amount of yielding in their maturity; while the growth and yield of the crop such as rice and wheat are greatly hampered without fertilization or high amount of pig manure nitrogen input, with varied amount of soil ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) in varied growth stages. Compared with single application of chemical fertilizer, pig manure application has improved the aboveground biomass during maturity by 6.48%-17.42% for rice and for wheat by 1.42%-28.25%, the final rice yielding by 0.96%?11.31% and final wheat yielding by 0.44%-19.38%.(4) With the application of inorganic fertilizer, the increased input of straw would improve the concentration of ammonium and nitrate nitrogen in the soil. Meanwhile, straw-saturated filed will in turn promote plant height (wheat and rice), aboveground accumulation and their yields. Compared with single application of chemical fertilizer, applying both fertilizer and straw has improved the aboveground biomass during maturity by 8.45%?13.18% for rice, the final rice yielding up by 1.68%?2.14% and final wheat yielding by 3.93%?5.34%.(5) With total amount of straw put into field, varied amount of pig manure exerts a great impact on the final yield of rice and wheat. With 50% pig manure substitute for chemical fertilizer, the rice plant height exhibits the most obvious advantage and the season rice yields mount to 8227 kg/hm2, up by 9.58% as opposed to single fertilizer application. The same case goes to wheat growth, with season wheat yields mount to 4614kg/hm2, up by 3.63%, and the obvious advantage of plant height as well.Thus, considering the soil nitrogen mineralization, growth indices in different periods and the final yield analyzed above,50% pig manure nitrogen+50% nitrogen fertilizer+Straw(total amount) is the best favorable application mode for the rice-wheat rotating area in Chengdu plain. |
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