土区长期施肥对小麦-玉米轮作体系钾素平衡与钾库容量的影响

本文研究了土区小麦-玉米轮作体系长期氮磷钾化肥不同配合施用方式及氮磷钾化肥与秸秆或有机肥配合施用对钾素平衡以及土壤钾库的影响。试验包括9个处理，分别为不施肥（CK）、单施氮（N）、氮钾（NK）、磷钾（PK）、氮磷（NP）、氮磷钾（NPK）、氮磷钾配合一季秸秆还田（SNPK）、氮磷钾配合低量有机肥（M1NPK）和高量有机肥（M2NPK）。结果表明，除NK、PK和M2NPK处理外，其它处理小麦和玉米钾的携出量均大于钾的投入量，导致土壤钾素处于亏缺状态，20年累计亏缺量为6174333 kg/hm2。与试验前相比，长期施肥种植没有显著影响土壤全钾含量； 长期施用钾肥显著提高土壤速效钾含量，但长期不施钾肥处理的土壤速效钾含量也未显著降低； 无论施钾与否土壤非交换性钾（Mactotal K）以及非交换性钾中更容易被HNO3溶解提取的钾（Step K）均明显低于试验前水平。表明土壤非交换性钾可以作为该土壤钾素消耗的指标。考虑到施钾肥的经济投入和现有资源高效利用（如秸秆、有机肥），从长远的角度出发，维持土壤钾素肥力以及土地可持续生产力，土区小麦-玉米轮作体系采用秸秆全部还田或施有机肥是必要的。

Potassium balance and pool as influenced by long-term fertilization under continuous winter wheat-summer maize cropping system in a manural loess soil

The long term effects of various combinations of nitrogen(N),phosphate(P),and potassium(K) application,NPK integrated with crop straw or organic manure on potassium balances and potassium pools were studied under continuous winter wheat-summer maize cropping system in a manural loess soil in Shaanxi of China.The long term experiment included nine applications of the recommended doses,un-amended control(CK),nitrogen(N),nitrogen and potassium(NK),phosphorus and potassium(PK),nitrogen and phosphorus(NP),nitrogen phosphorus and potassium(NPK),wheat/maize straw(S) with NPK(SNPK) and dairy manure(M) with NPK(M1NPK and M2NPK).The results show that except for the NK,PK and M2NPK treatments,the total K removals by crops exceed the quantities of total K applied to the soils in other treatments,where the net negative K balances were observed ranging from 617 kg/ha in the plot of M1NPK to 4333 kg/ha in NP treated soils over 20 years.Compared with soil total K content of the initial soil at the start of experiment,the long term fertilization and cultivation have no significant effects on soil total K.Nevertheless,soil available potassium contents are significantly increased by the long term addition of potassium(containing fertilizers or manure),but it remains unchanged on the treatments without K addition.The contents of non-exchangeable K extracted in 9 sequential extractions with boiling 1 mol/L HNO3(Mactotal K),particularly Step K,which is considered to be the most soluble fraction of Mactotal K,are substantially lower than their initial values,which suggests that Step K could be used as an indicator of K depletion for the investigated soil.Considering the cost of K fertilizer and the efficient use of existing K resources(such as straw,manure),incorporation of crop straw/stalk or organic manure into soil is,therefore,necessary in the long run under continuous winter wheat-summer maize cropping system in the manural loess soil in order to maintain soil K fertility and sustain land productivity.