Effects of combined application of organic manure and chemical fertilizers on soil nitrogen availability and movement under water and fertilizer saving management in cucumber-tomato double cropping system

A long-term experiment of combined application of organic manure and chemical fertilizers was conducted to determine changes in soil NO-3-N contents at depths of 0-40 cm(rhizosphere) and 40-100 cm,and leaching losses of mineral and organic N through 0-100 cm soil profile under water and fertilizer saving management(OPT management: N-P2O5-K2O application rates were 600-300-525 kg/ha for winter-spring cucumber and 450-225-600 kg/ha for autumn-winter tomato) in winter-spring cucumber and autumn-winter tomato double cropping system.The results showed significant decreases of NO-3-N contents in 0-100 cm soil profile and N leaching loss in leakage water,and distinct increases of economic incomes with the OPT management,indicating the huge water and fertilizer saving potentials in greenhouse vegetable production in farmer' s conventional water and fertilizer management.There was no insignificant differences in soil NO-3-N contents at depths of 0-40 cm during the growth period and 40-100 cm at the end of the growth period when 1/4-1/2 of chemical N was replaced by N from pig manure.With the increase ratio of pig manure N in the total applied N,leakage water volumes and N leaching tend to increase.When 1/2 of chemical N was replaced by N from straw,NO-3-N contents in 0-40 cm soil and the residual NO-3-N contents in 40-100 cm soil profile decreased by 34.3%-56.2% and 42.5%-87.8% respectively,and leakage water volumes and NO-3-N leaching amount decreased by 65.0% and 82.0%,yields and economic incomes kept stable.For newly built greenhouses with lower nitrogen supply in soil,chemical fertilizers only or combined application of chemical fertilizers and pig manure are suitable.These pattern could increase soil N supply in a short time.For greenhouses used for serveral years with continuous cropping obstacles,the proper fertilizer management patterns used are combined application of chemical fertilizers and pig manure in winter-spring cucumber season and chemical fertilizers and straw in autumn-winter tomato season,which could immobilize excessive NO-3-N in soils and decrease the risk of N leaching losses.