Long-term Fertilization Effects On Soil Fertility, Wheat Yield And Nutrient Use Efficiency On Lou Soil

The soils, in most areas of Loess Plateau, are in poor fertility,which severely limits theimprovement of crop yield. Many results have shown that the key measures to improve cropyield and to maintain the sustainable agricultural development are improving soil fertility byincreasing the application of fertilizer. However, unreasonable applying of fertilizer not onlyreduces the resources use efficiency, but also may cause the ecological and environmentalproblems. This study investigated the effects of long-term fertilization on soil properties andwheat yield and nutrient use efficiency based on the20-years long-term experiments on Lousoil in Guanzhong Plain, Shaanxi province, China. The experiments included seventreatments, which are application of recommended doses of nitrogen （N）, nitrogen andphosphorus （NP）, phosphorus and potassium （PK）, nitrogen, phosphorus and potassium（NPK）, dairy manure （M） with NPK （MNPK） and un-amended control （CK）. The mainresults obtained are as follows:1. Differed fertilization regimes had no significant effects on soil pH, while the soil pHunder MNPK treatment had a significantly decline trend. Application of NP, NPK and MNPKsignificantly increased SOM contents compared with CK by16%⁵9%. But there were nosignificant differences in TN content among treatments. Application of NP, PK, NPK andMNPK also significantly increased TP and AP contents compared with CK by27%-73%and4-13.6times, respectively. Long-term application of K fertilizers had no significant effects onsoil TK content, but significantly increased soil AK content by38.8%-98%over CK.2. Long-term unbalanced fertilization （N, NK, PK） had no significant effects ondistribution of water stable aggregates and its SOC and TN contents. Application of NP, NPKand MNPK had lower water stable aggregate contents in size>2mm and1²mm comparedwith CK. Application of MNPK also significantly increased water stable aggregate contents insize between0.25and1mm. The fertilization, especially organic materials plus inorganic fertilizers significantly increased SOC and TN levels in all sizes of aggregates, SOC and TNcontents in order were MNPK> NPK> NP> NK> PK> N> CK. The allocation of SOC andTN to different sizes of aggregates mainly depended on water stable aggregates contents,about60%of SOC and TN were allocated to the aggregate in size less than0.25mm.However the increased SOC by addition of organic manure was mainly allocated to theaggregates in sizes between0.25mm and1mm..3. The positive yield trends of wheat in all the treatments as a function of time wasobserved, and the treatments those receiving N and P fertilizer exhibited significantly positivetrends, the annual increment was from219to295kg ha^-1. The apparent N balance at thesystem level was positive in all treatments except for those N-omitted, and the most positivebalance were observed on N and NK treatments, the annual increment was88kg ha^-1and66kg ha^-1. The apparent P balance at the system level was positive in all treatments except forthose P-omitted, and the most positive balance were observed on MNPK treatment, the annualincrement was107kg ha^-1.The RE, AE and PEP of N（P）fertilizers in all treatments rangedfrom11.7%to50.7%,0.31to20.14kg kg^-1,11.71to34.48kg kg^-1and6.3%to20.9%,8.33to60.71kg kg^-1,41.07to98.74kg kg^-1, respectively. The RE, AE and PEP of N（P）fertilizersin treatments which received N and P fertilizer was higher than other treatments. The apparentK balances were negative in all treatments except for PK and MNPK treatments, and the mostnegative balance was observed on NP plot, the annual reduction was103kg ha^-1. Long-termapplication of K fertilizers had no significant effects on RE, AE and PEP of K fertilizers. Inshort, the application of NP or manure properly combined with nitrogen might be suitable forwheat-fallow system on the tested soil.