Effects Of Nitrogen Fertilizer On Wheat Growth And Soil Property Under Straw Mulching In Dryland

Natural resources such as photo-thermal energy and large arable lands abound in drylandof China. Straw mulching is one of the available measures to improve crop production in thisarea. Straw mulching could regulate soil temperature and improve soil water conservation,soil fertility, soil physical and chemical properties, which finally increase crop yields.However, some studies suggested crop yield could not always be increased under strawmulching, which probably depended on soil water and nutrients supply. An8-years fieldexperiment was conducted to investigate the effects of nitrogen rate on winter wheat growth,WUE, NUE, soil temperature and soil fertility under straw mulching. Here the last four yearsresults were reported.1. Compared with no mulching, tiller number in winter and total number of stems inspring under straw mulching decreased from2008to2012. At early filling stage, dry matteraccumulation of the grain under straw mulching was significantly lower than that of nomulching. Grain number and kernels weight under straw mulching both showed decreasedtrends compared with no mulching, which eventually led to the decreased winter wheat yieldunder straw mulching from2008to2012for one-year-fallow-winter wheat system in thisregion. The nitrogen rate for the highest yield and economic optimum yield were obtainedthrough the fertilizer response equation, which were275kg/hm~2and250kg/hm~2under strawmulching and225kg/hm~2and207kg/hm~2without mulching, respectively.2. Compared with no mulching, grains N, P and K uptake of winter wheat under strawmulching revealed decreased trends. Nitrogen use efficiency (NUE) and water use efficiency(WUE) under straw mulching reduced. Whether mulching or not, NUE and WUE could beimproved in150kg/hm~2-225kg/hm~2N rate.3. The average temperature of mulched soil was significantly higher during early winterperiod (6th Dec. to20th Jan.) and was significantly lower during the rest periods of wheatgrowth compared with no mulching treatment. The highest soil temperature during a day waslower than that of no mulching treatment while the lowest soil temperature during a day washigher especially during early winter period, which indicated the significantly decreasedtemperature changes of mulched soil. Straw mulching had a slighter effect on soil temperature of20cm compared with10cm. Greater difference of20cm soil temperature betweenmulching and no mulching treatment was found at grain filling stage than other stages ofwheat growth. Four years results showed straw mulching decreased wheat yield, whichpossibly caused by increased soil temperature of mulching treatment during early winterperiod and decreased temperature during later winter period.4. As N rate increased, soil water storage and distribution of soil moisture in the0-2msoil profile after harvest decreased significantly, while nitrate accumulation showed theopposite trend. Compared with no mulching, water storage and nitrate accumulation ofmulched soil after harvest increased and decreased, respectively. Straw mulching andreturning for8years demonstrated trends of improving active organic matter, total N,available P and available K content in surface soil after harvest, and eventually significantlyincreased total organic matter by3%-4%compared with the control.