秸秆还田条件下不同供钾能力土壤水稻、油菜、小麦钾肥减量研究

【目的】研究不同供钾能力土壤在秸秆还田条件下钾肥减量施用对水稻、油菜、小麦的产量、钾素吸收量及钾肥利用率的影响,计算秸秆还田条件下3种作物的钾肥适宜用量,为秸秆还田条件下钾肥资源的合理利用及农田钾素养分管理和调控提供理论依据。【方法】2013—2015年在湖北省38个县(市)的水稻、油菜及小麦3种作物上开展秸秆还田钾肥减量施用田间试验。试验设置6个处理,分别为(1)对照,不施钾(CK);(2)施用全量化学钾肥(+K);(3)秸秆还田处理(+S);(4)秸秆还田配施50%钾肥(S+1/2K);(5)秸秆还田配施75%钾肥(S+3/4K);(6)秸秆还田配施全量钾肥(S+K)。参考不施钾肥处理的作物相对产量(即CK处理产量/+K处理产量)将土壤供钾能力分为高、中、低3个水平。【结果】不同供钾水平土壤施钾和秸秆还田均能不同程度增加水稻、油菜和小麦的产量和地上部钾素吸收量。其中,高供钾能力的土壤水稻、油菜和小麦仅通过上季作物秸秆全量还田即可满足作物高产的钾素需求;中等供钾能力的土壤3种作物可在秸秆还田条件下减少50%钾肥用量;而低供钾能力的土壤,秸秆还田条件下水稻季可减少25%钾肥用量,油菜和小麦季可减少50%钾肥用量。从土壤钾素表观平衡来看,秸秆还田可缓解土壤钾素亏缺,其中油菜季平均盈余量为14.1—152.6kg K_2O·hm~(-2),小麦季平均盈余量为25.5—95.9 kg K_2O·hm~(-2),水稻季则仍表现为钾素亏缺。在考虑秸秆钾素投入量的情况下,通过一元二次方程和线性加平台方程拟合秸秆还田条件下钾肥用量与作物产量之间的关系,以+K处理产量为标准得到秸秆还田条件下的适宜钾肥用量。结果表明,在前茬作物秸秆全量还田的条件下,供钾能力为中、高等水平的土壤3种作物钾肥适宜施用量为20—33 kg K_2O·hm~(-2),油菜钾肥施用量低于水稻和小麦;而供钾能力低的土壤上,秸秆还田土壤钾肥适宜施用量为45—49 kg K_2O·hm~(-2),油菜钾肥推荐用量高于水稻和小麦。与目前钾肥经济施用量60 kg K_2O·hm~(-2)相比,3种作物在供钾能力为中、高等水平的土壤通过秸秆还田可节省钾肥45.0%—66.7%,供钾能力低的土壤也可节省钾肥18.3%—25.0%。【结论】秸秆还田条件下水稻、油菜及小麦可以在减少18.3%—66.7%钾肥用量的同时保证作物产量,钾肥施用量减少的比例应根据土壤供钾水平进行调整。

Study of Optimum Potassium Reducing Rate of Rice,Wheat and Oilseed Rape Under Different Soil K Supply Levels with Straw Incorporation

【Objective】 The experiments were conducted to study the effect of reducing potassium (K) fertilizer rates with straw incorporation on crop yield of cereal and oil, K uptake and K efficiency under different soil K supply capacities of Hubei, in order to provide a scientific basis for K fertilization and soil K management under straw returning. 【Method】 Field trials in 38 counties (cities) were carried out to study the effect of the substitution of straw incorporation for K fertilizer on rice, winter oilseed rape and wheat. Six treatments were designed: (1) no K fertilization (CK), (2) chemical K fertilization (+K), (3) straw incorporation (+S), (4) straw incorporation with 50% of chemical K fertilization (S+1/2K), (5) straw incorporation with 75% of chemical K fertilization (S+3/4K), and (6) straw incorporation with 100% of chemical K fertilization (S+K). Three soil K supply levels (i.e., HSKS, MSKS, and LSKS) were graded by relative yield (i.e., crop yield in the CK treatment divided by crop yield in the +K treatment) refer to the CK treatment. 【Result】 Both K fertilization and straw incorporation improved crops yield and K uptake under different soil K supply levels. Total straw incorporation only (+S) would satisfy crops K needs to achieve high yield level (i.e., crop yield in the +K treatment) for the HSKS. For the MSKS, 50% of chemical K fertilization with straw incorporation was needed to reach crop yield level of +K treatment. In case of LSKS, chemical K application rate could reduce 25% for rice and 50% for oilseed rape and wheat under straw incorporation condition, respectively. For the apparent K balance, straw incorporation could offset soil K deficit to some extent. For the seasons of oilseed rape and wheat, straw incorporation to the field could surplus 14.1-152.6 kg K₂O·hm^-2 and 25.5-95.9 kg K₂O·hm^-2, respectively. However, soil K balance would still be deficit during the rice season across the sites. The relationship between K fertilization rate and crop yield with straw incorporation was fitted by quadratic and linear-plateau models. The optimum K application rate was obtained from the model under the crop yield of the +K treatment. With straw incorporation, optimum K application rate was 20-33 kg·hm² for the three crops under the HSKS and MSKS levels, where oilseed rape required less K fertilizer than rice and wheat. However, optimum K rate was 45-49 kg K₂O·hm^-2 for the LSKS level, where oilseed rape needed more K fertilizer than rice and wheat. Compared with current K economic fertilization rate (60 kg K₂O·hm^-2), chemical K rate could be reduced by 45.0%-66.7% for the HSKS and MSKS levels, and also chemical K fertilizer could be saved by 18.3%-25.0% for the LSKS level. 【Conclusion】 Chemical K fertilizer could be saved by 18.3%-66.7% while guaranteed crop yields under straw incorporation condition. The reducing rate of chemical K fertilizer should consider soil K supply level.