Transformation And Movement Of Soil Nutrients Under Greenhouse Vegetable-rice Rotation

Greenhouse vegetable-rice crop rotation has the characteristics of excessive fertilization in the greenhouse vegetable cultivation period and the alternation of wetting and drying during the rice planting.Thus the transformation and movement of soil nutrients under greenhouse vegetable-rice rotation is quite different from traditional greenhouse vegetable cultivation and rice-upland crop rotation.In this study,effects of rice rotation on soil nutrients transformation and movement under greenhouse vegetable-rice crop rotation were investigated based on soil survey and field experimentation with three different crop rotation systems,including greenhouse eggplant-rice rotation(GER),greenhouse eggplant-summer fallow without plastic covering(GEF)and wheat-rice rotation(WRR)in Changxing county,Zhejiang province.The environmental risk of greenhouse vegetable-rice crop rotation was also evaluated.The results showed as follows.1.The organic matter,total N and Olsen-P in the 0-20 cm of GER soil were increased by 150%,36.7%and 26.0 times,respectively,compared to those at the beginning of the crop rotation systems.However,the accumulation of soil available nutrients was lower compared with GEF.Rice planting in GER reduced the concentration of soil nutrients sharply in the 0-20 cm layer.The concentrations of NO3--N,Olsen-P and available K in the 0-20 cm soil depth decreased by 68.0%,25.2%and 16.7%,respectively,after the rice rotation in summer.Rice rotation showed no clear influence on nutrient leaching.The total N and NO3--N contents over the 20 cm soil depth in GER were lower than those in GEF at equivalent soil depth.The nitrogen content of percolate in GER showed no clear enhancement during the flooded water period.2.There was no significant acidification and secondary salinization in the 0-20 cm soil depth under greenhouse eggplant-rice rotation.Rice rotation in GER showed an obvious effect on the alleviation of soil acidification and secondary salinization.The pH in 0-20 cm soil depth enhanced 1.2 units.The exchangeable acidity and exchangeable H+ decreased by 70.0%and 57.8%after rice planting,respectively.The soil EC value and salt content in GER decreased by 67.7%and 80.9%,respectively,after rice planting.Greenhouse eggplant-rice rotation did not increase soil acidic ions and salt infiltration.The soil exchangeable acid,exchangeable H+,exchangeable salt ions and water-soluble salt ion content below 20 cm soil depth were significantly lower than that in GEF soils.3.Greenhouse eggplant-rice rotation enhanced the nitrification intensity and urease activity of topsoil and rhizosphere soil during the cultivation of eggplant,and the soil microbial biomass increased significantly,but did not change the community structure of soil ammonia oxidizing bacteria(AOB).Greenhouse eggplant-rice rotation reduced the rate of ammonia volatilization in soil,and the total amount of accumulated ammonia was 76.7%lower than that of GEF,but increased the nitrate reductase activity and the risk of nitrogen denitrification.4.The P adsorption intensity in soil was enhanced under GER.The values of the maximum P adsorptions(Qm),P adsorption constant(K)and maximum P buffer capacity(MBCP)of GER were higher than those of GEF.While the soil P desorption amount and desorption rate were decreased in GER when compared with that in GEF.Rice rotation in GER reduced the risk of soil phosphorus loss in comparison to GEF,and soil P surplus and degree of P saturation(DPS)were significantly lower than that of GEF.5.Nitrogen was the nutrient limiting factor in GER,and P and K were not.Soil P and K had an obvious aftereffect in GER.The supply of soil P and K exceeded 90%of the crop uptake in greenhouse eggplant and rice season.The crop yield did not decrease obviously in case of no P or K fertilizer applied during greenhouse eggplant and rice planting.