渗漏是三峡库区砂质土橘园氮磷流失的主要途径

Leaching Is the Main Pathway of Nitrogen and Phosphorus Losses for Citrus Orchards with Sandy Soil in Three Gorges Reservoir Area

过量施肥引起的氮磷流失是影响三峡库区水环境的重要因素。以三峡库区砂质土生草覆盖梯田橘园为研究对象,开展了不同施肥水平下的小区试验,连续2年对地表径流和渗漏液中的氮磷流失情况进行了观测。结果表明:(1)小区水分主要通过渗漏流失,地表径流系数低,土壤侵蚀弱。(2)深穴埋施施肥对地表径流氮磷流失无显著影响。(3)渗漏损失是小区氮磷流失的主要途径,分别占全氮和全磷总流失量的99.0%和76.9%。(4)氮磷流失量占施肥量的34.5%和6.4%,其中渗漏流失的氮磷分别占施肥量的34.3%和5.1%。(5)施肥引起的渗漏液氮流失量(y)随着施肥量(x)的增多而增大,二者具有极显著的线性相关关系(y=0.35x-5.77,P<0.01);而施肥引起的渗漏液磷流失量与施肥量无显著的相关性(P=0.05),主要因为一部分磷肥被根系利用,大部分残余的磷肥被耕层土壤吸附,仅有少量磷肥下渗至深层土壤,并且建园改土深层残余磷素对渗漏磷流失产生了影响。可见,砂质土梯田橘园养分渗漏流失,尤其是氮渗漏流失需要足够关注,养分管理需进一步优化,以减少流失,实现高效利用。

【Objective】Citrus production is one of the main income of farmers in the Three Gorges Reservoir area.The loss of nitrogen and phosphorus caused by excessive fertilizer in the Three Gorges Reservoir area presents negative impacts on the aquatic environment.【Methods】In this study,sandy soil citrus orchard with natural grass mulching was chosen.The amount of nitrogen and phosphorus loss from surface runoff and leaching was observed for two consecutive years by plot experiment at six levels of fertilization.The pathways of nitrogen and phosphorus losses in the citrus orchard and the effects of different fertilization levels on nitrogen and phosphorus losses were investigated.Seven treatments were set in the experimental plot,with an average row and plant spacing of 4.7 m×3.4 m;with no fertilizer application(T1)as the control,the application rates of nitrogen,phosphorus and potassium fertilizer for the T3,T4,T5,T6 and T7 treatments were 1.67,2.33,3.00,3.67 and 4.33 times those of T2,respectively.During the growth season of navel orange in 2016—2017,rainfall and atmospheric deposition of nitrogen and phosphorus were monitored.Surface runoff water,sediment,and infiltration water were sampled for total nitrogen(TN)and total phosphorus(TP)content.【Results】Under the ecological protection mode of grass mulching,the surface runoff and soil erosion were effectively controlled.The main pathway of water loss in the rain-fed citrus orchard was leaching with a low coefficient of surface runoff and weak soil erosion.During the study period,the rainfall loss by seepage accounted for 48.9%of the rainfall,and the surface runoff only accounted for 1.73%of the rainfall.The amount of fertilization applied in deep furrow had no effect on the amount of nitrogen and phosphorus loss from the surface runoff.Leaching was the main pathway of nitrogen and phosphorus loss.The average leaching loss of total nitrogen and total phosphorus accounted for 99.0%and 76.9%of the total loss of nitrogen and total phosphorus respectively.Also,the amount of nitrogen loss(y)by seepage increased with the increase of application rates(x),and there was a significant linear correlation between them(y=0.35x-5.77,P<0.01).However,no significant correlation existed between the amount of phosphorus loss and application rates(P=0.05).Also,only a small amount of phosphorus can be leached to the bottom of the soil after the roots uptake and soil particles adsorption in up layers.Moreover,the residual phosphorus in the deep soil,after deep plough before citrus planting,had an impact on the leakage of phosphorus.【Conclusion】The problem of nutrient loss,leaching nitrogen loss in citrus orchards,in particular,should be given more attention.To reduce nutrient loss and achieve efficient utilization,nutrient management should be further optimized.