The feedbacks between crop yield and soil organic carbon and total nitrogen contents were examined in a long-term experiment, which was established on black loessial soil on the Loess Pla-teau in China. There were six treatments, including CK (no fertilizer), N (single nitrogen fertilizer), NP (chemical fertilizers NP), SNP (straw and chemical fertilizers NP), M (organic manure) and MNP (organic manure and chemical fertilizers NP). Results showed that balanced application of chemical fertilizers, single application of organic manure, the combined application of chemical fertilizers with organic manure and chemical fertilizers coupled with straw returning to the field all significantly increased crop yield and its stability compared with control (CK). The yields of maize and wheat in NP, SNP, M and MNP treatments increased by 92%, 97%, 93%, 141% and 147%, 164%, 139%, 214%, respectively, compared with the control. The annual mean yields of maize and wheat in NP treatment were equal to or higher than those of the local conventional fertilization practices and quite stable among different years, which indicated that the fertilization rates with N 90 kg·hm-2 and P2O5 75 kg·hm-2 were enough for crop growth in wheat-maize rotation system. Application of chemical fertilizer P every other year combined with straw returning to the field (SNP) had similar crop yield values with NP treatment, with the P application amount could be reduced by 50%. The balanced application of chemical fertilizers, organic manure application, the combined application of chemical fertilizers with organic manure, and chemical fertilizers coupled with straw returning to the field could significantly increase soil organic carbon content, whereas chemical fertilizer application had no significant influence on soil total nitrogen content. Across all treatments, the contents of soil organic carbon and total nitrogen were significantly and positively correlated. Under different fertilization treatments, organic carbon sequestration rate was between 15% and 41%. In SNP treatment, the soil organic carbon content enhanced 0.06 g·kg-1 when the amount of organic carbon input every increased 1 t·hm-2, while in CK, N, NP, M and MNP treatments, the increments was between 0.12 and 0.15 g·kg-1. The yields of both maize and wheat were positively correlated with soil total nitrogen content. Maize yield constantly increased with the increases of soil organic carbon content, but wheat yield increased at first and then kept stable with the increases of soil organic carbon content, with a threshold of 6.8 g·kg-1. In conclusion, long-term balanced application of chemical fertilizers, organic manure application, chemical fertilizers combined with manure and chemical fertilizers coupled with straw returning to the field could significantly increase soil organic carbon and total nitrogen contents, consequently resulted in higher crop yield and stubble amount returned to soil, the increase of stubble returned to soil further led to the increase of soil organic carbon and total nitrogen contents, which formed the mutual promotion feedback relationship each other in the black loessial soil region of Loess Plateau in China.
通过设置在黄土高原黑垆土区的长期定位试验系统,研究了长期施肥条件下作物产量与土壤碳氮的互馈关系.试验设不施肥(CK)、单施氮肥(N)、氮磷配施(NP)、秸秆与氮磷配施(SNP)、施有机肥(M)和有机肥与氮磷配施(MNP)6个处理.结果表明: 与对照相比,长期平衡施用化肥、单施有机肥、化肥与有机肥配合施用和秸秆还田配施化肥显著增加了作物产量及其稳定性, NP、SNP、M、MNP处理玉米和小麦产量分别增加92%、97%、93%、141%和147%、164%、139%、214%.NP处理玉米和小麦年均产量与当地常规施肥作物产量相当且稳定,小麦-玉米轮作体系施肥量为N 90 kg·hm-2、P2O5 75 kg·hm-2能够满足作物需要.秸秆还田与隔年施磷相配合的SNP处理与NP处理作物产量相似,且可减少磷肥施用量50%.平衡施用化肥、有机肥、化肥与有机肥配施和秸秆还田配施化肥均可显著增加土壤有机碳含量,而施用化肥对土壤全氮含量影响不明显,综合所有处理,土壤有机碳和全氮含量呈显著正相关.不同处理土壤有机碳固存率在15%～41%.SNP处理土壤有机碳累积投入量增加1 t·hm-2,土壤有机碳含量增加0.06 g·kg-1,而CK、N、NP、M和MNP处理的增幅在0.12～0.15 g·kg-1.玉米和小麦产量都与土壤全氮含量呈显著正相关,玉米产量随土壤有机碳含量的增加而增加,但小麦产量随土壤有机碳含量的增加先快速增加后趋于平稳,拐点出现在6.8 g·kg-1.长期平衡施用化肥、有机肥、有机肥与化肥配合施用及秸秆还田配施化肥可显著增加黄土高原黑垆土土壤有机碳和全氮含量、作物产量和根茬还田量,根茬还田量的增加又进一步增加了土壤有机碳和全氮含量,形成了相互促进的互馈关系.
Keywords: Loess Plateau; black loessial soil; feedback relationships; organic carbon; total nitrogen.