| The Loess Plateau dryland is one of the largest wheat producing areas.However,the excessive use of chemical nitrogen(N)fertilizer during winter wheat production has caused not only wastes of resources,but also decreases of N use efficiency,soil and crop quality,and a series of environmental problems(eg.greenhouse gas emission,surface and underground water pollution).Therefore,there has been an increasing interest of pursuing a more environmental-friendly method to reduce the chemical N fertilizer rate and achieve a sustainable development of agricultural system.Besides,as a typical rainfed area where rainfall is the sole water source for agricultural production,The Loess Plateau is facing great challenge of a scant water supply and nutrient deficit during its wheat production.Finding ways to effectively use water and to sustain productivity are crucial for dryland farming in the Loess Plateau.Combining manure with chemical fertilizer can not only retain water,improve soil structure and fertility,and promote the immobilization of chemical N,but also improve the soil environment,and enhance soil nutrients supply.Within this context,organic substitution technology has become an important pathway to reduce the chemical N fertilizer application rate and solve the "drought" and "poor soil fertility" problems in the Loess plateau in recent years.However,some studies have shown that the unreasonable ratio of combined application of manure and chemical fertilizer would result in a lack of soil moisture,an increasing risk of nitrate leaching to the deep soil layer.Therefore,in order to explore the reducing rate of chemical N fertilizer through adding manure,and determine a recommended ratio of chemical-N and manure-N,the study was conducted following a split-plot design in the Loess Plateau to investigate the effect of a combined use of manure(sub-treatment)and five N fertilization rates(0,75,150,225 and 300 kg N/hm2;main treatment)on grain yield,nutrients and water uptake of winter wheat,and nitrate-N residue in the soil layer.The main results were as follows:(1)Compared with single chemical fertilization treatment,combining manure with 0~225 kg N/hm2 increased winter wheat yield by 14.1%~27.8%,and combining manure with 0~150 kg N/hm2 chemical N fertilizer improved aboveground biomass of winter wheat by 31.2%~39.2%.Under the manure condition,the grain yield and aboveground biomass of winter wheat increased first and decreased afterwards with the increase of chemical N application rate.No further increases were observed when N rate excedded 75 kg N ha-1 with the presence of manure.The regression equation between winter wheat yield and N application rate showed that,the combined application of manure and chemical fertilizer could increase wheat yield by 13% and reduce the N fertilization rate by 18% compared with applying chemical fertilizer alone.(2)Combining manure with moderate rate of chemical N fertilizer(less than 150 kg N/hm2)increased the grain N content by 12.0%~13.0%,N uptake by 25.1%~39.2%,and N use efficiency(NUE)by 3.1~11.7 percentage points,compared with applying chemical fertilizer alone.At the N rate of 75 kg N ha-1,NUE and the agronomic efficiency of applied N(NAE)of winter wheat were significant higher than other N rates when combined with manure.Besides,the combination of manure and chemical fertilizer could promote the uptake of P and K with less chemical N input compared with the single application of chemical fertilizer.(3)Compared with applying chemical fertilizer alone,although additional manure consumed more soil water in deep layer,resulting in lower soil water content(under 160 cm layer)after winter wheat harvest,it can reduce the soil water loss and improve soil water storage efficiency during summer fallow season significantly,and then improve the winter the water use efficiency of wheat.Under manure condition,chemical N input could also promote the water use of winter wheat,and N rate of 75 and 150 kg N ha-1 resulted in a significant higher water use efficiency(WUE)than other N rates.(4)Manure application not only reduced the nitrate-N residue in 0~200 cm soil layer when combined with low rate of chemical N fertilizer(0~75 kg N/hm2)by 25.2%~27.0% after winter wheat harvest,but also reduced the amount and depth of nitrate-N leaching during summer fallow season,whereas improved soil nitrate-N residue,nitrate-N leaching amount and depth when chemical N input was over 150 kg N/hm2,compared with applying chemical fertilizer alone.According to the regression equation of soil nitrate-N leaching amount and chemical N application rate,the chemical N input of 133 kg N/hm2 is the critical nitrogen fertilizer.When the N application rate was less than the critical value,the additional manure could reduce the nitrate leaching loss of 0~200 cm soil layer during winter wheat summer fallow season.To sum up,combining manure with chemical fertilizer could reduce the chemical N application rate by 13%,with an improvement of witner wheat yield.A combined application of 30 t/hm2 cattle manure(about 24 kg N/hm2)with 75~133 kg N/hm2 chemical N fertilizer(manure-N: chemical-N =1: 3.1~5.5)was recommended in the winter wheat production system of Loess Plateau dryland,in order to reduce the chemical N amount,and achieve sustainable winter wheat production system in the Loess Plateau. |
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