长期秸秆还田下基于东北水稻高产和钾素平衡的钾肥用量研究

  【目的】  通过5年定位试验，系统研究东北稻区秸秆还田条件下不同钾肥用量对水稻产量、钾素利用率和土壤供钾能力的影响，为秸秆还田下水稻钾肥合理施用提供科学依据。  【方法】  于2015—2019年在东北水稻主产区吉林省前郭县开展田间定位试验。共设6个钾肥用量 (K₂O) 处理，分别为0 (K0)、30 (K30)、60 (K60)、90 (K90)、120 (K120) 和150 kg/hm2 (K150)，水稻收获后，测定籽粒产量与生物产量、植株钾含量及0—20和20—40 cm土层土壤速效钾、缓效钾和全钾含量，并计算作物钾积累量、钾素利用效率和土壤-作物系统的钾素表观平衡状况。  【结果】  施钾可提高水稻籽粒产量和生物产量，与不施钾相比，平均增幅依次为7.6%～14.5%、6.3%～10.9%，以K60和K90处理籽粒产量和生物产量最高。不同施钾处理间收获指数没有显著差异。钾素表观回收率、农学利用率和偏生产力均随钾肥用量的增加而下降。K60、K90、K120和K150处理0—40 cm土壤速效钾和缓效钾含量高于K0和K30处理，全钾含量6个处理间没有显著差异。K90、K120和K150处理0—40 cm土壤速效钾和缓效钾含量间也没有显著差异。在5年试验中，K0和K30处理土壤钾素表观平衡均表现为亏缺，K60处理农田钾素投入量和输出量基本平衡，当钾肥用量增加至90 kg/hm2以上，农田钾素表观平衡呈现盈余状态，并随钾肥用量的增加显著增加。盈余率与钾肥用量、籽粒产量、土壤速效钾含量、钾素利用效率分别进行拟合得出，当盈余率为0时，钾肥用量为53.1 kg/hm2，籽粒产量为10035 kg/hm2，0—20和20—40 cm土壤速效钾含量分别为103.04和91.56 mg/kg，钾素表观回收率为40.4%，钾素农学利用率为21.2 kg/kg，钾素偏生产力为202.2 kg/kg。  【结论】  在秸秆还田条件下，施用钾肥对水稻依然有明显增产效果。年施K₂O 30 kg/hm2，土壤钾素处于亏缺状态；年施K₂O 60 kg/hm2增产效果最好，且土壤钾素处于基本平衡状态，土壤速效钾和缓效钾含量处于稳定状态；年施K₂O超过90 kg/hm2后，虽然钾盈余量增加，但对土壤速效钾和缓效钾含量没有进一步增加的效果，水稻产量甚至还有下降的趋势。以理论盈余率为0时钾肥用量的95%为置信区间，钾肥用量在50～56 kg/hm2范围内既可保证较高的水稻产量和钾素利用效率，又可维持土壤供钾能力，可作为东北稻区秸秆还田下水稻钾肥推荐用量。

Optimum amount of potassium fertilizer based on high yield and soil potassium balance under straw return in rice production region of northeast China

  【Objectives】  The effects of different amounts of potassium (K) fertilizer on rice yield, K utilization efficiency and the capacity of soil K supply under straw return in rice production region of northeast China were systematically studied, in order to provide scientific basis for rational K fertilizer application under straw return of rice.  【Methods】  A located field experiment was conducted in Qianguo County of Jilin Province during 2015–2019. Six rates of K fertilizer (K₂O) treatments were setup, including 0 kg/hm2 (K0), 30 kg/hm2 (K30), 60 kg/hm2 (K60), 90 kg/hm2 (K90), 120 kg/hm2 (K120) and 150 kg/hm2 (K150). After harvest each year, the grain and biomass yield, K content in plant were measured, and the contents of soil readily available, slowly available and total K in 0–20 cm and 20–40 cm depth were analyzed. The K accumulation, K utilization efficiency and apparent K balance in soil were calculated.  【Results】  Compared with K0 treatment, the grain and biomass yields were averagely increased by 7.6%–14.5% and 6.3%–10.9%, with the highest yields in K60 and K90 treatments. The harvest indexes were not significantly different among the K treatments. K recovery efficiency, agronomic efficiency and partial productivity declined with increasing of K application rate. The treatments of K60, K90, K120 and K150 increased the contents of readily available K and slowly available K in 0–40 cm soil, but did not in the total K contents, compared with K0 and K30 treatment. There was no significant difference in readily available K and slowly available K in 0–40 cm soil among the treatments of K90, K120 and K150. The apparent K balance of soil were in deficiency under K0 and K30 treatments during the five-years period, just in balance under the K60 treatment, and surplus under the K90, K120 and K150 treatments. When surplus rate of K was 0, the simulated K application rate was 53.1 kg/hm2, the achieved grain yield would be 10035 kg/hm2, readily available K contents in 0–20 cm and 20–40 cm soil be 103.04 mg/kg and 91.56 mg/kg, and the K recovery efficiency, agronomic efficiency and partial productivity be 40.4%, 21.2 kg/kg and 202.2 kg/kg, by simulating between K fertilizer rate, grain yield, soil readily available K content, K utilization efficiency and surplus rate, respectively.  【Conclusions】  Under the tested condition, the soil K apparent balance will be in deficit when annually K₂O rates is less than 30 kg/hm2, just in balance when K₂O 60 kg/hm2 is applied, and in surplus when K₂O rate is higher than 90 kg/hm2. The high rice yield will be achieved at K₂O rate of 60–90 kg/hm2, and the soil readily available and slowly available K contents will not be further increased at K₂O rate higher than 90 kg/hm2. The simulated application rate with annual soil K surplus of zero is at the range of K₂O 50–56 kg/hm2, in which the rice yield, the K fertilizer utilization efficiency and the capacity of soil K supply will be the highest under this experimental condition.