小麦玉米轮作体系氮、磷吸收与平衡研究

当前在作物生产中氮磷资源的不合理利用严重威胁环境，为了探讨华北山前平原冬小麦-夏玉米轮作体系合理的氮磷配合措施，在几年水氮（水磷）定位试验基础上对氮磷吸收与利用状况进行了分析。试验为小麦-玉米周年轮作种植，设水氮和水磷试验，水分为主区，施氮（磷）量为副区，裂区试验设计。水分设置限水和适水2个处理，周年设置6个施氮水平，小麦＋玉米氮肥用量分别为0＋0，60＋60，120＋120，180＋180，240＋240，300＋300 kg ／hm2；3个施磷水平，小麦季磷肥用量分别为75，150，225 kg ／hm2，玉米季不施磷。结果表明，施氮（磷）可提高作物地上部分吸氮（磷）量，小麦和玉米全年施氮量240 kg ／hm2即可达到较高的地上部总吸氮量，限水和适水下施氮量分别为218．7，243．5 kg ／hm2才能保证氮素盈余量为零。小麦和玉米全年施磷量75～150 kg ／hm2可达到较高的地上部总吸磷量，但限水和适水下施磷量分别为49．4，69．9 kg ／hm2才能保证磷素盈余量为零。冬小麦对氮和磷的生产效率低于夏玉米，限水和适水下百千克籽粒吸氮量小麦分别为2．4，2．3 kg，平均为夏玉米的1．42倍；百千克籽粒吸磷量小麦均为0．61 kg，平均为夏玉米的1．23倍。当限水和适水下土壤全氮含量分别达0．102％和0．097％、全磷含量分别达0．213％和0．209％时土壤即可保持养分盈余量为零。土壤水分含量较高使植株对氮磷的吸收量也较高，但百千克籽粒吸氮（磷）量却表现出相反的趋势。在华北山前平原区小麦玉米轮作体系周年施氮量218．7～243．5 kg ／hm2、施磷量49．4～69．9 kg ／hm2可实现氮磷盈余量为零。

Effects of N, P and K on Output and Nutrient Cycle of Vegetables in Greenhouses

ObjectiveThe aim was to increase farmers’ income and reduce the waste of fertilizer by exploring effects of N, P and K fertilizations on vegetable yields and the accumulation of N, P and K in vegetable and soils. MethodThe fertilization tests were conducted on tomato, cauliflower and celery in greenhouses. ResultWhen N, P and K were not applied in tomato, cauliflower or celery, the yields reduced in 6.0%-13.8% and total annual income reduced by 39 220, 36 902 and 22 023 yuan/hm 2 respectively, suggesting that N, P and K are limiting factors of yield. The absorbed N amounts of tomato and cauliflower were higher compared with celery; the absorbed P amount of cauliflower was higher compared with tomato and celery; the absorbed K amount of tomato was the highest, followed by celery and cauliflower. The absorbed N in tomato fruit was lower than that of cauliflower and the absorbed N amount of other parts of tomato was also lower. Furthermore, the absorbed amounts of P and K by tomato and cauliflower fruits were higher than it absorbed by the other parts, especially the absorbed of K was significantly high. Total absorbed amounts of N, P and K from high to low were cauliflower, tomato and celery. After harvesting of tomato, cauliflower and celery, N, P and K in soils were all higher compared with soils before planting. Influenced by fertilizers, residual N content in soils grown with tomato and residual P content in soils grown with celery both doubled compared with base soils. Cauliflower plants were not applied with organic fertilizer, and residual N and K contents in soils were lower compared with tomato and celery. ConclusionResidual P content in soils is higher, which is a kind of waste and would cause pollution on soils. It is necessary to improve the proportion of organic and inorganic fertilizers in fertilization.

Combined Applications of Nitrogen and Phosphorus Fertilizers with Manure Increase Maize Yield and Nutrient Uptake via Stimulating Root Growth in a Long-Term Experiment

Imbalanced application of nitrogen(N) and phosphorus(P) fertilizers can result in reduced crop yield,low nutrient use efficiency,and high loss of nutrients and soil nitrate nitrogen(NO_3^--N) accumulation decreases when N is applied with P and/or manure;however,the effect of applications of N with P and/or manure on root growth and distribution in the soil profile is not fully understood.The aim of this study was to investigate the combined effects of different N and P fertilizer application rates with or without manure on maize(Zea mays L.) yield,N uptake,root growth,apparent N surplus,Olsen-P concentration,and mineral N(N_(min)) accumulation in a fluvo-aquic calcareous soil from a long-term(28-year) experiment.The experiment comprised twelve combinations of chemical N and P fertilizers,either with or without chicken manure,as treatments in four replicates.The yield of maize grain was 82%higher,the N uptake 100%higher,and the N_(min) accumulation 39%lower in the treatments with combined N and P in comparison to N fertilizer only.The maize root length density in the 30-60 cm layer was three times greater in the treatments with N and P fertilizers than with N fertilizer only.Manure addition increased maize yield by 50%and N uptake by 43%,and reduced N_(min)(mostly NO_3^--N) accumulation in the soil by 46%.The long-term application of manure and P fertilizer resulted in significant increases in soil Olsen-P concentration when no N fertilizer was applied.Manure application reduced the apparent N surplus for all treatments.These results suggest that combined N and P fertilizer applications could enhance maize grain yield and nutrient uptake via stimulating root growth,leading to reduced accumulation of potentially leachable NO_3^--N in soil,and manure application was a practical way to improve degraded soils in China and the rest of the world.

Soil Respiration, Microbial Biomass and Nutrient Availability in Soil After Addition of Residues with Adjusted N and P Concentrations

Microbial activity and nutrient release are known to be influenced by organic matter properties,but it is difficult to separate the effect of C/N ratio from that of C/P ratio because in most plant residues both ratios are either high or low.An incubation experiment was conducted to investigate the effects of reducing the C/N and C/P ratios of slowly decomposable plant residues(young eucalyptus leaves,mature wheat straw,and sawdust) to those of rapidly decomposable residues(young kikuyu shoots) on soil respiration,microbial biomass,and N and P availability.The C/N and C/P ratios of the former were adjusted to 15 and 89,respectively,by adding N as(NH_4)_2SO_4,P as KH_2PO_4 or both and residues were added at 10 g C kg-1 to a silt loam.Soil respiration was measured over21 d;microbial biomass C(MBC) and available N and P were measured on days 0,7,and 21.Compared to the unamended soil,addition of kikuyu increased cumulative respiration 20-fold,MBC concentration 4 to 8-fold,and available P concentration up to4-fold,whereas the increase in available N concentration was small and transient.Cumulative respiration and MBC concentration were low in the sawdust-amended soil and were not influenced by reducing the C/N and C/P ratios.Cumulative respiration with original wheat and eucalyptus was 30%-40%of that with kikuyu.Reducing the C/N ratio alone or both C/N and C/P ratios increased cumulative respiration and MBC concentration 2-fold compared to the original wheat and eucalyptus,whereas reducing the C/P ratio had little effect.Throughout the experiment,the available N concentration after addition of residues with reduced C/N ratio increased in the following order of eucalyptus < wheat < sawdust.By independently lowering the C/N and C/P ratios,microbial activity was more limited by C and N than P.However,lowering the C/N ratio of very slowly decomposable sawdust had no effect on soil respiration and MBC concentration,suggesting that other properties such as concentration of poorly decomposable C compounds limited decomposition.