Effect of cultivation year on tomato growth and soil nitrogen supply ability of newly built solar greenhouses

Solar greenhouse, developed by China’s farmers and scientists in the early 1980s, makes it possible to produce vegetables during winter without additional heating and lighting in large parts of North China. Vegetable cultivation in greenhouses has high profitability. This has led to a rapid increase in the land area used for solar greenhouse production over the last three decades. Within the greenhouse system, it is common to overuse inorganic fertilizers and manure in vegetable production. It increases the organic matter in soil and the accumulation of nutrients and salts in the soil. The accumulation of nutrients in solar greenhouse soils, especially nitrate, has high environmental risks. Optimum application of nitrogen (N) fertilizer is critical for resolving this problem. Mineralized N in soils during crop growth supports a high rate of N uptake by crop. Therefore understanding nitrogen (N) mineralization in solar greenhouse soils with different cultivation histories is important for rational N fertilization. However, most of the studies on soil N mineralization studies have focused on arable soils and little remains known about N mineralization in solar greenhouse soils with different cultivation histories. In this study, the pot depletion method and Stanford and Smith aerobic incubation method were used to evaluate the effects of cultivation years on N supply ability in the 020 cm layer of soil under newly-built solar greenhouse with different cultivation years 0 year (before greenhouse construction), 2 and 3 years of operation in Yangling, Shaanxi. Response of tomato to cultivation years was also investigated. The results showed that tomato height, stem diameter, aboveground and root biomass, leaf SPAD in 2 and 3 years greenhouse were significantly higher than those in field of 0 year greenhouse, while these indexes were not significantly different between 2 years and 3 years greenhouses. Total N uptake of tomato increased with increasing age of solar greenhouse. Total N uptakes in greenhouse soils with 2 and 3 years of cultivation were 2.53 and 3.01 times that of soils before greenhouse construction. Soil organic matter, total nitrogen and available nutrients contents of 3 years solar greenhouse were significantly increased compared with those of field before greenhouse construction. Mineralized N in solar greenhouse soils with 2 and 3 years of cultivation was 2.84 and 2.96 times that of soils before greenhouse construction. It then indicated that as the age of solar greenhouse increased, soil N supply ability increased significantly. The contents of soil organic matter, total N, initial mineral N, and mineralized N were significantly positively related to tomato N uptake. The coefficient between mineralized N and tomato N uptake was highest. It indicated that these indexes could be used to evaluate soil N supply ability, mineralized N was the best one. In order to reduce N loss and increase N use efficiency in the study area, it was concluded that as the age of greenhouses increased, the addition of inorganic N fertilizer should be reduced in solar greenhouse production.