Study On Effects Of Poplar-crop Intercropping System On The Soil Nitrogen Loss

The process and characteristics of nitrogen loss along with the runoff and leaching flowwere investigated in poplar-crop intercropping systems. Effects of different levels of fertilizingtreatment were also studied on the nitrogen cycling and soil nitrogen accumulation inintercropping systems. Some main factors and action machenisms were identified affectingtheir nitrogen loss process. Research results could be a reference for practices in the alleviationof agricultural non-point pulltion, the increase of nitrogen use efficiency, the improvement ofwater environment in Taihu Lake area and the establishment of poplar-crop intercroppingsystems. The main conclusions were described as follows:(1)The results indicated that there existed a positive correlation between the quantity ofleachate water and precipitation. In intercropping ecosystem poplar trees could reduce thequantity of eluviated solution by canopy interception. The intercropping ecosystem couldreduce N leaching effectively and avoid N further moving into shallow groundwater. Thenitrogen leaching had spatial heterogeneity in intercropping ecosystem and changed with thedifferent stand density and different distance to the poplar row.(2)Surface runoff and sediment increased with the increase of rainfall intensity.Compared with the monoculture land of wheat, intercropping systems could decrease amountsof total nitrogen loss and sediment carried away by runoff. Some specifical patterns of TN lossand nitrate concentration were discovered with time. In early runoff stage the concentration washigher, and the reduced or kept stabile in middle stage, and in the end the concentrationreascended. The ammonium nitrogen concentration decreased with the time increasing.(3)The intercropping ecosystem could definitely improve soil nutrient status in the depthof0²0cm. Compared with monoculture land of wheat, intercropping ecosystem decreased thecontent of NO₃--N and NH₄⁺-N in the depth of20⁸0cm. The results showed there existed bothhorizontal and vertical variances of the content of soil nitrate in intercropping ecosystem. Thenearer the the distance of plot to the poplar row is, the more variation extent there existed.(4)Some specifical patterns of NO₃--N content changes appeared in the wholedevelopment stage of wheat. The content of nitrate in0⁴0cm soil layer came to the peak valueat the earring stage, and then decreased with increasing time. Before the heading stage, thecontent of nitrate was relatively lower in40⁸0cm soil layer, and then the content reascended.(5)Both root length density and biomass of wheat decreased with the increase of soildepth. The roots mainly distributed in the upper soil layer of0²0cm. The root length densityand biomass of wheat changed with different wheat development stages, the total dry weight ofroot in0⁸0cm soil layer reached its peak value at the filling stage. In monoculture system of wheat, the root length and dry weight in0⁸0cm soil layer were greater than those of theintercropping ecosystem in every development stage. In poplar-wheat intercropping system, thenearer the distance of the wheat root system to the poplar row is, the less the root system will be.The fine root length density and biomass of poplaer trees decreased with the increase of soillayer depth. The nearer the distance to the tree row was, the greater they were. There existed aniche overlapping are between poplar tree and wheat in such intercropping system.(6)In^<sup>15N micro-plot experiment, the utilization rate of nitrogen fertilizer by theamaranth decreased with the increase of N application level. The N use efficiency ofintercropping system significantly increased. Applying N fertilizer increased the nitrate contentsin0⁸0cm soil layer.Intercropping ecosystems could significantly decrease the¹⁵N losses andloss rate of N fertilizer compared with pure crop land.