水稻-大麦长期轮作体系钾肥效率及土壤钾素平衡

Study on Potassium Use Efficiency and Apparent Soil Potassium Balance Under Long-Term Rice-Barley Rotation

【目的】研究水旱轮作系统中土壤自然供钾力、钾肥利用率和土壤钾素表观平衡,为农田钾素的可持续性管理提供理论依据。【方法】设置不施肥(CK)、施氮磷肥(NP)和施氮磷钾肥(NPK)3个处理,利用20年稻麦水旱轮作定位试验数据,研究大麦和水稻地上部生物量、产量及籽粒和秸秆中含钾量对不同施肥处理的响应。【结果】在一年两熟和三熟制稻麦轮作系统中,20年不施肥(CK)的作物平均每年可生产籽粒8.24和9.22 t·hm-2,其相当于相应轮作体系平衡施肥(NPK)的75.6%和71.9%,因此施肥对作物产量提高的贡献率分别为24.4%和28.1%,施钾肥对作物籽粒产量提高的贡献分别为11.8%和14.0%。钾肥对旱季作物的增产贡献率高于水季,其中钾肥对大麦产量提高的贡献率平均为17.9%,比水稻的高36.1%。在一年两熟和三熟轮作制中,不施肥的作物平均每年从土壤中吸收的钾量相当于相应平衡施肥的59.1%和58.3%。作物地上部吸钾量的绝大部分来源于秸秆。其中大麦地上部吸钾量的81.7%来源于秸秆,水稻为74.2%—87.6%。旱季土壤钾素自然供应能力低于水季。大麦生长期平均每年土壤钾素自然供应能力为69.8%,比早稻、连作晚稻和单季晚稻分别低15.5%、19.7%和19.4%。随着试验时间的延长,大麦生长期土壤钾素自然供应能力以每年1.6%的速率降低,但水稻生长期土壤供钾能力在时间上没有显著变化,20年定位试验后仍维持在80%以上。尽管施钾肥降低了作物钾素内部利用率,但是年度间各施肥处理作物钾素内部利用率没有显著变化。在平衡施肥条件下,每吸收1 kg钾素,大麦、早稻、连作晚稻和单季晚稻可生产籽粒平均为42.4、44.7、41.3和44.8 kg。每施入1 kg钾肥可生产籽粒分别为83.5、79.7、71.6和69.7 kg。旱季钾肥效率高于水季。在一年两熟轮作制中钾肥表观利用率平均为29.5%,而在一年三熟轮作制中,表观利用率可达41.5%。由于作物对钾素不断的吸收,造成在一年两熟和三熟水旱轮作系统中不施肥(CK)的土壤每年钾素亏缺148.2和182.7 kg·hm-2,而且施氮磷肥加速了土壤钾素的耗竭,每年多携带走钾素57.8和65.0 kg·hm-2。尽管施钾肥缓解了土壤钾素不足,但在一年两熟和三熟轮作制中施钾土壤平均每年仍亏钾分别为146.5和85.5kg·hm-2。【结论】在水旱轮作系统中,水稻生长期土壤供钾能力高于麦季,但旱季钾肥的利用效率高于水季,在年施钾量(K2O)187.5 kg·hm-2的条件下,土壤钾素仍表现亏缺,因此,应该重视土壤钾素平衡问题。

[Objective]The potassium （K） natural productivity from soil, K fertilizer use efficiency and apparent soil K balance were investigated to provide a theoretical basis for the sustainable management of K element in farmland. [Method]The three fertilizer treatments used were control, NP and NPK, representing various combinations of N, P and K fertilizer applications.Long-term （over 20 years） experiments with barley-rice crop rotation were conducted to investigate the response of crop aboveground biomass, yield, the K content in grain and straw to different application treatments. [Result]The results indicated that the grain yields on average were 8.24 and 9.22 t？hm-2 per year in barley-single crop rice and barley-early rice-late rice rotation cropping system without application fertilization for 20 years, which accounted for 75.6%and 71.9%of that in NPK treatments in the corresponding rotation system. The contribution of application fertilizers increased crop grain yields by 24.4%to 28.1%, and the contribution of K fertilizers increased crop grain yields by 11.8%to 14.0%in barley-single crop rice and barley-early rice-late rice rotation cropping system, respectively. The contribution of K fertilizers increased grain yields for barley （17.9%） was 36.1%higher than that for rice. The annual K uptakes from CK treatments accounted for 59.1%and 58.3%of that in NPK treatments. The K in straws accounted for 81.7% and 74.2% to 87.6% of total K uptake for barley and rice, respectively. The indigenous K supplying capacity in barley season was lower than that in rice season. The annual indigenous K supplying capacity for barley on average was 69.8%, which were 15.5%, 19.7% and 19.4% lower than that for early rice, late rice and single crop rice, respectively. The indigenous K supplying capacity in barley season decreased significantly over cultivation time at an average rate of 1.6%per year. But there was no significant change of the indigenous K supplying capacity in time during rice cropping. The indigenous K supplying capacity in rice season still was more than 80% after 20 years cropping. The internal K use efficiency was decreased because of K application. But there was no significant change of internal K use efficiency among treatments in time. Under balanced fertilization with fixed N, P and K inputs, the internal use efficiencies for barley, early rice, late rice and single-crop rice were 42.4, 44.7, 41.3 and 44.8 kg＆#183;kg-1, respectively. The partial factor productivity in NPK treatment was 83.5, 79.7, 71.6 and 69.7 kg＆#183;kg-1, respectively. The K use efficiency in barley season was higher than that in rice season. The apparent K recovery efficiency was 29.5% and 41.5% in barley-single crop rice and barley-early rice-late rice rotation system, respectively. Crop continuous uptake caused a net K lost of 148.2 and 182.7 kg＆#183;hm-2 per year in the soils without application of fertilizer in barley-single crop rice and barley-early rice-late rice rotation cropping system, respectively. Moreover, the application of nitrogen and phosphate fertilizer accelerated soil K depletion, the extra K amount of 57.8 and 65.0 kg＆#183;hm-2 was taken up by crop. Although K deficiency in soil could be relieved by K application, a net K lost of 146.5 and 85.5 kg＆#183;hm-2 per year in soils received K fertilizer from barley-single crop rice and barley-early rice-late rice rotation cropping system. [Conclusion]There was a very strong capacity to provide K element from soils during rice growing season. But the K fertilizer use efficiency in barley season was higher than that in rice season. There was a still net K loss from soil with K application rate of 187.5 kg K 2 O＆#183;hm-2 per year. So a great attention should be paid to the apparent soil K balance.