华北平原农田裂缝对硝态氮淋溶的影响

The effects of farmland cracks on nitrate leaching in the North China Plain

土壤干缩开裂是常见的自然现象。目前关于土壤干缩开裂的研究主要集中于裂缝的最终形态特征,并且以室内试验为主。本研究通过室外大田试验,结合动态计算机图像分析及水氮运移模拟软件WHCNS,研究土壤干缩开裂的动力学过程、特征及其对农田水氮运移的影响。利用原位熔化石蜡浇筑得到了裂缝三维结构形态,借助三维激光扫描仪量化裂缝的几何特征,发现每平米裂缝平均长度为4.58 m,裂缝上表面平均宽度为5.72 mm,平均深度为9.06 cm。基于三维扫描仪提取得到的裂缝几何参数,通过WHCNS仿真模拟,发现相较于无裂隙情况,裂隙的存在分别增加了传统施肥和优化施肥情况下97.40%和256.43%的硝态氮淋失量;与优化施肥模式相比,传统施肥模式更容易造成硝态氮的淋失风险。在模拟灌溉模式对硝态氮淋洗情况的影响时,其差异不明显;强降雨的设置同样增加了硝态氮的淋失风险,导致硝态氮的年均淋洗量增加83.61%。裂缝的存在严重影响农田作物对肥料的吸收和利用,通过优化施肥量、更改灌溉模式以及避免强降雨前施肥都可以减少肥料的损失。

Desiccation cracking is a common soil natural phenomenon.Research on desiccation cracking has mainly focused on morphological characteristics in lab-based experiments.In this study,three-dimensional(3D)geometric crack structures were extracted using paraffin casting in the field and transient image processing.The influence of cracks on farmland water and nitrogen leaching was quantified using the Water Heat Carbon Nitrogen Simulator(WHCNS)model.The 3D structural characteristics of the cracks obtained by the laser scanner were as follows:average length per square meter=4.58 m,average surface width=5.72 mm,and average depth=9.06 cm.WHCNS analysis showed that cracks increased nitrogen leaching(97.40%,traditional fertilizer;256.43%,optimized fertilizer),and that traditional fertilizer application had a greater nitrate nitrogen leaching risk.Irrigation type did not affect nitrate leaching,but heavy rainfall increased the risk and led to an 83.61%annual leaching volume increase.Additionally,the WHCNS model was used to simulate the effects of fracture,fertilization,irrigation,and rainfall intensity on nitrate leaching.The results showed that cracks had a notable influence on nitrate nitrogen leaching using optimal and traditional fertilization methods,and optimized fertilization reduced nitrate nitrogen leaching.Precipitation intensity was a key factor affecting nitrogen leaching.In this study,the simulation only calculated the nitrate nitrogen leached to underground and ignored nitrogen runoff from heavy precipitation,reducing the effect of precipitation on nitrogen leaching;however,the timing and amount of fertilizer and precipitation should be considered together when managing fields,especially in the summer,when rainfall is concentrated.The simulation showed that irrigation did not affect nitrate nitrogen leaching,which may be related to irrigation intensity and the leaching soil layer(100 cm)set by the model.However,the basin irrigation amount simulated in this study could not leach nitrate nitrogen below the 100 cm soil layer,which may have contributed to the small differences between methods.Thus,sprinkling irrigation and optimized fertilization should be adopted in combination to take full advantage of the water and fertilizer saving methods.