长期秸秆还田对华北潮土肥力、 氮库组分及作物产量的影响

【目的】近年,华北小麦-玉米轮作系统秸秆全量还田已逐步普及,但秸秆还田下土壤氮库组成的变化并不清楚。本文利用肥料定位试验,研究了长期秸秆还田(32年)对华北潮土肥力、 氮库组分和作物产量的影响。【方法】研究选用河北省衡水旱作试验站长期定位试验的不施肥(对照CK)和等量氮、 磷肥用量下的0kg/hm2(S0)、 2250 kg/hm2(S1)、 4500 kg/hm2(S2)和9000 kg/hm2(S3)秸秆还田处理。于2012年小麦收获后采集各处理020 cm土样,利用新鲜土样测定微生物量氮、 NH+4-N和NO-3-N;风干土壤用常规方法测定氮磷钾全养分、 有机质和pH,用Bremner法测定有机氮(酸解氨基酸态氮、 酸解氨态氮、 氨基糖氮和酸解未知态氮),用Silver-Bremner法测定固定态铵。同时结合长期试验数据, 分析长期秸秆还田下有机质和作物产量的变化。【结果】与试验开始前(1981年)相比,长期施用化肥处理的土壤全磷和有机质显著增加,全氮没有明显变化,而全钾出现降低趋势(-3.2%);秸秆用量的增加提高了全氮、 全磷和有机质,降低了pH值,但对全钾没有影响。酸解氨基酸态氮、 酸解氨态氮和未知态氮为潮土有机氮的主要组分;与CK相比,长期施肥提高了土壤有机氮含量,酸解氨基酸态氮、 酸解氨态氮和氨基糖氮均随秸秆用量的增加而增加,而不同施肥处理对酸解未知态氮和非酸解氮没有明显影响。长期化肥施用提高了微生物量氮和晶格固定态铵,秸秆用量的增加进一步提高了微生物量氮,但降低了固定碳铵。施肥没有明显影响NH+4-N含量,但长期施用化肥提高了NO-3-N含量,且高量秸秆还田对NO-3-N含量的提高具有促进作用。施肥显著提高了作物产量,在施用化肥基础上增施秸秆进一步提高了小麦和玉米产量,且玉米产量随秸秆用量的增加而增加,而高量秸秆还田对小麦产量并没有显著影响。【结论】长期化肥(氮、 磷肥)和秸秆结合施用提高了土壤肥力(主要为氮、 磷), 增加了土壤碳固持,但仅玉米秸秆还田导致了土壤钾消耗,增加钾肥投入维持土壤钾平衡是必要的。长期秸秆还田对酸解氨基酸态氮的贡献高于酸解氨态氮;高量秸秆还田提高了微生物量氮和NO-3-N含量,但降低了固定态铵含量。长期秸秆还田提高了作物产量,而为保证秸秆还田后茬的作物高产,与之配套的还田方法和田间管理是很必要的。

Effects of long-term straw return on soil fertility,nitrogen pool fractions and crop yields on a fluvo-aquic soil in North China

【Objectives】Recently, both wheat and maize straws return is widespread in a winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation system in North China, but the changes of soil N pool fractions under the straw return are not clear. We studied effects of straw return on soil fertility, N pool fractions and crop yields by a long-term fertilizer experiment.【Methods】We chose a no-fertilizer control (CK) and maize straw return at rates of 0 kg/ha (S0), 2250 kg/ha (S1), 4500 kg/ha (S2) and 9000 kg/ha (S3) combined with nitrogen (N) and phosphorus (P) fertilizers from the long-term fertilizer experiment in Hengshui Dryland Farming Experimental Station, Hebei province. Soil samples (0-20 cm) were collected in each plot after wheat harvest in 2012. We determined soil microbial biomass N, NH+4-N and NO-3-N with fresh soil samples. With air-dried soil samples, we determined soil total N, total P, total potassium (K), organic matter, and pH using conventional methods, and analyzed soil organic N (hydrolysable amino acid N, amino sugar N, ammonia N and hydrolysable unknown N) and fixed ammonium using the methods of Bremner and Silver-Bremner, respectively. Additionally, the changes of soil organic matter and crop yields were analyzed using the data of the long-term experiment. 【Results】Compared with the initial nutrient contents(1981), long-term application of chemical fertilizers increases soil total P and organic matter, does not influence soil total N, and decreases soil total K (-3.2%). The increase in straw rates enhances soil total N, total P and organic matter, but decreases soil pH, and does not influence soil total K. The hydrolysable amino acid N, hydrolysable ammonia N and hydrolysable unknown N are mainly fractions of organic N in fluvo-aquic soil. Compared with CK, soil organic N is increased under the long-term fertilization, and the hydrolysable amino acid N, ammonia N and amino sugar N are all increased with the increase of straw rates, while the hydrolysable unknown N and non-hydrolysable N are not changed under different fertilization treatments. The long-term application of chemical fertilizers enhances soil microbial biomass N and fixed ammonium. The increase in straw rates further increases the microbial biomass N, but decreases the fixed ammonium. The fertilization treatments do not affect soil NH+4-N, but the application of chemical fertilizers increases soil NO-3-N, and higher rate of straw inputs further increases soil NO-3-N. The fertilization increases crop yields, and straw return on the basis of chemical fertilizers further increases crop yields. The maize yields are increased with the increase of straw rates; however, the increase in straw rates does not affect wheat yields.【Conclusions】 The long-term combined application of chemical fertilizers (N and P) and straw enhances soil fertility (mainly N and P) and quality, and increases soil C sequestration, but only maize straw return leads to serious depletion of soil K, and the increase of K fertilizer inputs is necessary to sustain soil K balance. The effect of the long-term straw return on hydrolysable amino acid N is greater than that on ammonia N, and the higher rates of straw return increase soil microbial biomass N and NO-3-N, but decreases fixed ammonium. The long-term straw return enhances crop yields, however, scientific straw return and field management practices are necessary to ensure high crop yields under straw return.