| Citrus is commonly grown in southern China and become one of the local pillar industries.In recent years,Chinese farmers applied more nitrogen(N)fertilizer to increase citrus yields.Resulting in reduced N utilization in citrus orchard and the excess soil N exacerbates environmental problems such as non-point source pollution.Previous studies have found that N fertilizer reduction improved N utilization while protecting citrus yields and benefit to China’s citrus industry.However,the effect of N fertilizer reduction on soil nutrient leaching is still not clear.To clarify the effect of N reduction on N leaching from citrus orchard.Our study based on the long-term field experiment in Dangyang city,Hubei Province,which includes four N fertilizer rates(N0: no N fertilizer,N70:70% of the local conventional N application rate,N85: 85% of the local conventional N application rate,N100: the local conventional N application rate)and three soil depths(0-30 cm,30-60 cm,60-90cm).The leaching samples were collected in each rainfall events.The physical and chemical properties of soil were combined with leaching samples to identify the effects of N fertilizer reduction on soil N,phosphorus(P)storage and the N,P leaching.Results of our study were as follows:(1)Compared with N100,the soil total N of N85,N70,N0 at each depth decrease-4.56%～17.63%,4.13%～33.63%,22.86%～44.10%;Soil total dissolved N decrease 10.11%～61.65%,45.36%～ 81.39%,95.87%～98.01%;Soil nitrate decrease 10.25%～23.59%,-0.61%～14.64%,81.07%～87.48%;Soil ammonium decrease-13.10%～33.65%,-12.99%～50.48%,22.82%～54.42%;Soil alkali-hydrolyzable N decrease-82.14%～49.98%,-118.21%～74.71%,58.14%～83.99%.N fertilizer reduction generally reduce soil N storage,with no significant effect on soil total N storage.In each treatment,soil particulate N was the main form of soil N.(2)Compared with N100,the soil total P of N85,N70,N0 at each depth decrease 17.66%～19.33%,-1.00%～14.72%,-15.50%～19.30%;Soil available P decrease 21.86%～65.68%,5.38%～47.34%,33.01%～69.72%.N fertilizer reduction had no significant effect on soil available P.(3)Compared with N100,the total N leaching in N85,N70,N0 decrease34.00%～74.69%,39.14%～84.75%,95.42%～97.89% at each depth under 20 mm precipitation;The nitrate leaching decrease 39.52%～79.79%,41.21%～87.00%,96.95%～98.71%;The ammonium leaching decrease 37.83%～80.76%,56.75%～83.87%,86.48%～96.15%.N fertilizer reduction significantly reduced the amount of N leaching,and the nitrate was the main form of N leaching.(4)Compared with N100,the total P leaching in N85,N70,N0 decrease-30.00%～33.33%,9.23%～46.66%,-3.07%～60.00% at each depth under 20 mm precipitation;The total dissolved P leaching decrease-43.33%～61.53%,-3.33%～38.46%,-40.00%～53.84%;The soil particulate P decrease-28.57%～28.57%,20.00%～47.05%,25.71%～52.94%.N fertilizer reduction had less effect on soil P leaching,which was mainly concentrated in the soil surface.(5)The leaching of total N,nitrate and ammonium was almost positively correlated with N application rates and precipitation rates,while the leaching of total P,total dissolved P and particulate P had almost no significant relationship with N application rates and precipitation rates.Over all,N85 and N70 had no significant effect on soil N and P in each soil depth compared with N100,but effectively reduce the N and P leaching. |
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