Manure Nitrogen Availability And Its Substitution Ratio For Chemical Fertilizer Nitrogen

Appropriate and efficient use of organic and chemical fertilizers is important for improving crop yield/quality, soil fertility and protecting environment. Understanding release, transformation and availability of organic fertilizer nitrogen (N) and determining the optimal ratio of chemical and organic fertilizer N combination are the key solutions. In this study, laboratory incubation experiments and a greenhouse pot experiment were designed to investigate organic N mineralization of manures, transformation of organic N fractions and fertilizer equivalence of manre N. A microplot experiment using 15N and a field experiment were conducted in black soil-spring maize cropping system in Northeast China to study the appropriate substitution ratio of manure N for chemical N and its feasibility. The main results were summarized as follows:1.Laboratory incubation experiments were conducted using clay-loam black soil to study organic nitrogen mineralization and changes of organic N fractions of nine manures including 3 samples of chicken manure, pig manure and cattle manure, respectively. Results indicated that during incubation time the nitrate content increased and ammonium N decreased sharply within the initial 14 days. Soil accumulated mineral N increased with incubation time showing"S"trend during incubation period. The most rapid accumulation of soil mineral N was occurred in the period during 56 to 84 days after incubation when the amount of accumulated mineral N was accounted for 38.8%-98.5% of toal amount of accumulation within 161 days of incubation. The accumulation of soil mineral N increased slowly after 84 days of incubation and did not increase after 112 days of incubation. Net mineralization occurred after 28 days of incubation. A significan(tP<0.05)difference in net mineralization of organic N existed between manures and the average net minalization from chicken manure, pig manure and cattle manure was 21.0%, 19.1% and 13.1% of total organic N applied. During incubation time soil organic N fractions including amino acid N, ammonium N, amino sugar N, and hydrolysable unidentified N decreased, while non hydrolysable N was not significantly changed. Significant (P﹤0.05 or P﹤0.01) positive relationships existed between soil mineralized organic N and content of soil total hydrolysable N, amino acid N, ammonium N before incubation, while significant (P﹤0.05 or P﹤0.01) negative relationships existed between soil mineralized organic N and content of soil organic fractions after incuabation. Total hydrolysable N especially amino acid N is the main source of organic N fraction for N mineralization. It was estimated that about 1.7%-26.9% of organic N from 9 manures was mineralized during 161days incubation.2.A pot experiment was conducted by planting corn in black soil to investigate N availability of manure and its substitution equivalence for chemical N. Results showed that N availability of pig manure was 22.5%-38.3% with a mean of 30.6% when evaluated by recovery efficiency. The relative effectiveness (Rel Eff) of pig manure N was 27.2% when 120 mg N kg^-1 of pig manure was applied. The average relative fertilizer equivalence (RFE) calculated by relationship between chemical N and uptake N was 32.9%。 3.Micro-plot field experiment using ¹⁵N isotopic techniques was conducted from 2009 to 2010 to investigate crop response to various ratios of manure N substitutions for chemical fertilizer N at the same rate of N, P and K applied and the residue effect of ¹⁵N under black soil-spring maize system in Jilin. Results showed that compared with full chemical fertilizer N, 15% to 45% of organic N substitution for N did not significantly affected maize grain yield, crude protein production, content of essential and non-essential amino acid. Substitution of 30% manure N for chemical N could improve N uptake with an average N recovery efficiency of 60.3% for two years, which is 10-15 percentage point over full chemical N and other substitutions. The recovery of ¹⁵N by two season crops was 59.6%, 2.6-5.5 percentage point above full chemical N and other substitutions. The residual effect of ¹⁵N was limited with only 1.78%-2.36% N recovered in the second season. The ¹⁵N remained in different soil layers decreased with the increase of manure substitution. After the first season, ¹⁵N remained in 0-20 cm, 20-40 cm and 40-60 cm soil layer was 39.3%-47.6%, 2.9%-7.9% and 0.8%-2.4% of applied ¹⁵N, respectively, while after the second season ¹⁵N remined in various soil layers did not exceed 2.5% of applied ¹⁵N.4. Field plot experiment was conducted in black soil-spring maize system of Northeast China to evaluate the feasibility of manure N substitution for chemical fertilizer from agronomic and environmental aspects. Results indicated that the substitution of manure N for 30% of chemical N was superior or equivalent to full chemical fertilizer N or farmer practice (FP), in plant growth, dry matter/N accumulation and yield/quality, while it could reduce N, P and K rate and improve N use efficiency compared with FP. The substitution of 30% chemical N by the available N from manure double total N application, while N use efficiency was decreased, and no further increase of crop yield and quality was found. Therefore, the optimum pattern of N management in black soil-maize system in Northeast China was the combination of 30% manure with 70% of chemical fertilizer at the recommended N rate.