Study Of The Fate And Use Eiffciency Of Fertilizer Nitrogen Based On High Abundance Of¹⁵N

The north China plain is the main food production area in China. Winter wheat-summer maizerotation is the main cropping system in this region. Fertilizer application is an effective way to improvethe grain yield and food production. However, unreasonable nitrogen fertilization results in lowefficiency, large nitrate nitrogen residue in soil, and increasing loss, which will make a strong impact onenvironment. There are always three fates when the fertilizer was placed into the soil. Thetransformation and the fate of fertilizer in soil-crop system and the assimilation, utilization, andallocation in plant body are the theory basis of making reasonable fertilization rate and method. So it isnecessary to make the appropriate management measures that knowing the behavior of nitrogen in thesoil-crop system. For this, we set up the field¹⁵N-micropolt experiments in Xun county of Henanprovince, Langfang city and Gaocheng city of Hebei province, to research absorption characteristics,transformation and fate of winter wheat and summer maize by tracing method under optimum nitrogen、phosphorus and potassium supply in north China plain. This study provided a theory basis of evaluatingthe fertilizer utilization ratio in north China plain, clearing the conversion and fate of nitrogen placedinto the soil, abating environment pollution and applying nitrogen fertilizer reasonably. The mainconclusions were as follows:1: In the soil, nitrogen fertilization were able to promote the wheat grain yield increase, and theyield increasing rate ranged in8.43%-36.75%by applying nitrogen in this experiment, and nitrogencontribution rate were7.73%-26.87%, and the effect of increasing yield of fertilizer was quite obviousin low fertility soils.2: The nitrogen source of the whole winter wheat growth stage was researched with¹⁵N tracermethod. The results showed that: all of nitrogen assimilated by winter wheat, only26.56%-33.64%came from fertilizer, and as high as66.36%-73.44%came from soil. The reliance to the soil nitrogenwas very high, so, soil nitrogen was the main source of nitrogen during winter wheat growth season.3: The fate of fertilizer applied to soil was researched with¹⁵N tracer technology. The resultsshowed that: the utilization rate of the fertilizer was between22.11%-32.37%in the fist season, therange of total loss was11.32%-48.28%, and the ratio of soil residual was between29.61%-56.32%,60.34%-76.48%of the total nitrogen fertilizer residual centralized in0-40cm soil layer, the residualamount in surface was more than in the lower layer, the residual rate of¹⁵N fertilizer in the soil profiledecreased quickly with the increasing of soil depth.4: The residual fertilizer of winter wheat season could be assimilated by summer maize and theamount of residual fertilizer assimilated by summer maize was in the range of8.33-14.10kgN/hm₂,which accounted for2.72%-5.10%of the total amount uptake nitrogen, the total use efficiency ofsummer maize was in the range of3.47%-7.07%, namely the residual nitrogen fertilizer had a certainstimulative effect to the after crop. The loss amount of¹⁵N fertilizer in summer maize season was in therange of20.89-35.70kgN/hm₂, which accounted for8.70%-19.83%of the total fertilizer applied inwinter wheat season. The loss amount of¹⁵N fertilizer in summer maize season was in direct proportion to the residual amount after winter wheat harvest.5: After the harvest of summer maize, there were fertilizer which applied in winter wheat seasonresidued in the soil. The residual amount was in the range of41.82-55.20kg/hm₂in the layer of0-100cm, but the residual fertilizer mostly centralized in the surface, which the residual amount was in therange of22.97-30.05kg/hm₂. Compared to the residue amount of winter wheat, the residual amount of15N fertilizer was downward in vertical direction in the summer maize season. After the assimilation ofsummer maize, the decrement of15N was in inverse proportion to soil depth. That is to say, with theincreasing of soil depth, the decreasing amount of15N reduced gradually.6: After a winter wheat and summer maize rotation, the amount of15N assimilated by winter wheatwas from53.06kgN/hm₂to60.00kgN/hm₂, the15N assimilated by summer maize was only8.33-14.10kgN/hm₂, and the assimilation amount of the total rotation ranged from61.39to74.10kgN/hm₂. The15N use efficiency was between25.88%-38.10%in the whole rotation cycle. The lossratio in winter wheat season was11.32%-48.28%, and8.70%-39.80%in summer maize season. The lossratio in winter wheat season¹⁵Nhigher than summer maize season. The loss ratio of the rotationcycle ranged from31.15%to56.98%.The residual rate was from17.43%to30.67%after the rotation.7: The fertilizer use efficiency calculated by difference method was ranged in5.21%-10.63%, but22.11%-32.36%by trace method, which was higher than the former. It meant that application nitrogenfertilizer could inhibit soil nitrogen absorbed by corps in certain extant.