| Vegetable crop cultivated in solar greenhouse is a very intensive system in north China. The overuse of fertilizer is very common in this system. It degrades soil quality, and has negatively potential effects on environment, and seriously restricts the sustainable development of vegetable production in China. Many researchers have studied the accumulation of nutrients in the soil, and optimum water and fertilizer managements in this system. However, most of the studies on nutrient accumulations in soil with different ages was conducted using ‘space as a substitute for time’ method, in which soil samples of different ages was collected at the same time, to evaluate nutrient accumulations in soil. The varied management practices of different greenhouse confounds the effects of the cultivation years, and leads to big errors to evaluate the effects of the cultivation years on nutrient accumulations in soil. Additionally, greenhouse soils have the high organic matter content, and optimum water and heat conditions are favorable for nitrogen mineralization. However, the knowledge about the changes of soil nitrogen supply potential in greenhouse with different ages is limited. Therefore, it is worthwhile to quantify the changes of soil nutrient accumulations and nitrogen supply potential in the greenhouses. This will also contribute to develop scientific water and fertilizer management practices, increase fertilizer use efficiency and provent environmental pollution.To understand the nutrient inputs, vegetable yield, and nutrient accumulations in soil, more than 10 solar greenhouses in the southern part of Loess Plateau, Yangling, China were investigated over the four consecutive years since 2009. The topsoils from the greenhouses were used to investigate soil nitrogen supplying ability in the greenhouses soils of different cultivated years with pot experiment method, and the effects of temperature and water on soil nitrogen mineralization in solar greenhouses with different cultivation years with the incubation methods. A two-year experiment(2011-2013) was conducted to study the effect of different nutrient and water treatments on soil nutrient content and the yield of tomato(Lycopersicon esculentum Mill.) in solar greenhouse. The main results were as follows:(1) To understand the changes of nutrient balances and accumulations in soil of the newly-built solar greenhouse, 13 solar greenhouses in, Yangling, China were investigated over four consecutive years from 2009 to 2013. The results show that the average annual input rates of nitrogen(N), phosphorus(P2O5), and potassium(K2O) fertilizers in manure and inorganic fertilizer forms were 1804, 1565 and 1779 kg ha, respectively. Nutrient inputs from manures accounted for 64% of total N input, 58% of total P input, and 53% of total K input. The over-application of N, P, and K in the greenhouse was very common. As the greenhouse aged, organic matter, total nitrogen, available P and K in topsoil(0-20 cm) were significantly increased; and the increasing rates were more significant during the first and second years, then leveled off from third year to fourth year. Nitrate-N and electrical conductivity(EC) were also increased with greenhouse ages. The nitrate-N content in soil profiles showed clear leached down during the first 2-4 years. Although the average concentration of nitrate-N in well water in the solar greenhouse region was lower than the recommended level of nitrate-N in the drinking water, the great attention should be paid on the nitrate leaching risk due to the over-accumulation of nitrate in soil profiles as the aging of the solar greenhouse.(2) The N mineralization from soils layers of 0-20 cm and 20-40 cm with different cultivation years(before planting, the first year, second and third year after the planting) in five solar greenhouses since 2009, in Yangling, Shaanxi Province, was studied with Standford & Smith aerobic incubation method. The results showed that the amounts of the soil mineralized N increased with the cultivation years. For the greenhouse with same cultivation year, the accumulative mineralized N from 0-20 cm soil layer was higher than that in 20-40 cm soil layer. The first-order exponential model was used to simulate the dynamics of long-term soil N mineralization. The potentially mineralizable N(N0) was increased with the cultivation years. The N0 of the third year in the 0-20 cm soil layer was 290.0 mg kg-1. As the increase of cultivation year, it increased not only the mineralized nitrogen in the 0-20 cm soil layer, but also in the 20-40 cm soil layer. Regression analysis indicated that when soil organic matter increased 1 g kg-1, N0 in the 0-20 cm and 20-40 cm depth increased 22.63 and 8.41 mg·kg-1, respectively. Therefore, the N supply capacity from the solar greenhouse soil was increased significantly as the increasing cultivation years. In order to reduce the N loss and increase N use efficiency in study area, we suggest reducing the application rate of chemical nitrogen fertilizer as the increasing cultivation years of solar greenhouse.(3) An incubation method(84 d) was used to study effects of different temperature(20 ℃and 30℃) on nitrogen mineralization in the solar greenhouse soils. The first order reaction model was used to fit curve of soil N mineralization. The results showed, the contents of soil organic matter, total N, and the accumulative mineralized N in different greenhouses are increased with the increase of greenhouse ages. The soil mineralized N amount at 30 ℃ was higher than that at 20℃. The response of the mineralized N to temperature in soil with long cultivating history was higher than that in soil with short cultivating history. As the increases of soil temperature and the cultivating history, the soil mineralized N amount was increased, and the soil N0 was also increased. There was a positive interaction between soil temperature and the cultivating history. However, the difference was not significant. Compared to the soil before planting crops, the N0 values of soils with 2 and 3 years history were increased by 5.59 and 11.48 times, respectively. The regression analysis indicates that the N0 values of soils at 20 ℃and 30 ℃ were increased by 2.70 and 3.18 mg kg-1 when soil organic matter was increased by 1 g kg-1, and when soil total N content was increased by 1 g kg-1, the N0 values of soils at 20 and 30 ℃ ℃ were increased by 37.28 and 43.12 mg kg-1, respectively.(4) An aerobic incubation method was conducted to evaluate the effects of soil moisture(60, 80 and 100% of field capacity) and utilization age(0, 2 and 3a). Results showed that the accumulated nitrogen mineralization was increased with the cultivating years, and also increased with soil moisture. However, the accumulated nitrogen mineralization decreased when the soil moisture reached a certain value. There was a positive interaction between soil moisture and the cultivating years. As the increase of soil moisture and the cultivating years, the soil accumulated nitrogen mineralization was increased. Similarly, the nitrogen mineralization potential(N0) increased with the cultivating history and soil moisture, and the N0 decreased when the soil moisture reached to high range. The regress analysis indicated that N0 of soils at 60 FC, 80 FC and 100 FC are increased by 1.62, 1.88 and 1.57 mg kg-1 when soil organic matter was increased by 1 g kg-1, increased by 28.93, 33.42 and 27.82 mg kg-1 when soil total N was increased by 1 g kg-1. Therefore, the effects of soil moisture and cultivation history on N mineralize should be considered as factors for solar greenhouse vegetable N fertilizer management.(5) The pot depletion method and Stanford and Smith aerobic incubation method were used to evaluate the effects of planting years to nitrogen(N) supplying ability in soils(0-20 cm) of the newly-built solar greenhouse with different cultivation years(0, 2 and 3 year after the greenhouse was built) in Yangling, Shaanxi. The results showed that the tomato biomass and total N uptake increased as aging of greenhouse. Total N uptake in greenhouse soils with 2a and 3a of cultivation years was 2.53 and 3.01 times of soil before planting crop. And the mineralized N in greenhouse soils with 2a and 3a of cultivation years was 2.84 and 2.96 times of soil before planting crop. It indicates that as aging of greenhouse, soil nitrogen supplying ability was significantly increased. The contents of soil organic matter, total N, initial mineral N, and mineralized N were significantly positive to tomato N uptake. The correlation coefficient between soil mineralized N and tomato N uptake was more significant, it indicates that indicating aerobic incubation method was an effective method to evaluate soil N supplying ability. We concluded that as aging of greenhouse, the addition of inorganic N fertilizer should be reduced in solar greenhouse production.(6) A two-year experiment(2011-2013) was conducted to study the effects of different nutrient and water treatments on the growth and yield of tomato and on soil nutrient accumulation in solar greenhouses in south Loess Plateau, China. The results showed that compared to current fertilizer and water practice, the two formula treatments had at par tomato fruit yields; however, they saved 35-46% of the nitrogen(N) fertilizer, 40-54% of the phosphorus(P2O5) fertilizer, 19-35% of the potassium(K2O) fertilizer and 15-21% of irrigation water. The economic profits of FW1 and FW2 were higher than those of FW and FP treatments. The two formula treatments also reduced soil electrical conductivity(EC), and accumulation of nitrate, available P, available K in soil. The contents of the available nutrients in the soil were still high. Obvious N surplus in greenhouse was observed in different treatments, mainly due to high N input from manures. This study revealed that there is great potential to reduce nutrient and water use, while maintaining the same yield level in the greenhouse system. |
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