Nutrient Balance And Accumulation In Soils Of Solar Greenhouse In Shaanxi

Solar greenhouse is an efficient and low cost system to grow vegetables in regions with low temperature during winter. Therefore, it beomes popular since 1990 s in the North China. It is an important economic pillar industry in many areas. However,blind fertilization, especially excessive fertilization, is very common in solar greenhouse, which leads a series of environmental problems and soil degradation, seriously restrict the sustainable development of solar greenhouse. Many researchers have conducted a lot of studies in this aspect. However, it is difficult to accurately explain the dynamic changes of greenhouse soil nutrient accumulation with the increase of soil nutrient on using the method of "time generation space" in the previous study. Study on nutrient balance and accumulation about Shaanxi greenhouse mostly concentrated in the Guanzhong area, and few studies were done in northern areas of this province. In addition, to study the nutrient flows and characteristics of greenhouse from the perspective of system is rarely reported.Therefore, we study nutrient balance and soil nutrient accumulation in greenhouse of different regions of Shaanxi, and nutrient flow characteristics in greenhouse system. The main conclusions are as follows:⑴We have surveyed the application of fertilizers in greenhouses over two consecutive years(2013 and 2014) in Yangling, Ansai, and Jingbian of Shaanxi Province; and nutrient contents in the greenhouse soils were also determined. The results showed that, ① Total nutrient inputs from manures and chemical fertilizers varied with the regions. The average annual input amounts of N, P2O5 and K2 O were 1933.3, 1587.2 and 1799.2 kg/ha in study region, respectively. Chemical fertilizer was the main source of nutrient input amount in the greenhouse. The amounts of N, P2O5 and K2 O uptake by crops accounted for only 22%, 7% and 36% of nutrient inputed. It resulted in huge nutrient surplus in the greenhouse system. ② The contents of organic matter and total N in the soils were in medium or lower levels. More than 60% of nitrate accumulation in 0-2 m soil profile was distributed below 60 cm layer, indicating that nitrate leaching was worthy of attention. Soil available P and K contents were at high levels; it indicates that the excessive application of phosphorus and potassium was very common. ③ Compared with the Lou soil and Loessal soil, nutrient contents in aeolian sandy soil was relatively low. Therefore, we should pay attention to the effective application of organic manure and chemical fertilizers in this soil in north Shaanxi Province.⑵Nutrient inputs and outputs in more than 10 newly-built soalr greenhouses located in Yangling, Shaanxi were investigated, and soil samples from these greenhouses were also taken since their building over the past five years. The results show that the soil nutrient contents increased with greenhouse age, and signficant increase were observed in the surface soil(0-20 cm). The annually increases of soil organic matter, total nitrogen and available phosphorus, potassium were 3.5 g/kg, 0.2 g/kg and 24.8 mg/kg, 39.2 mg/kg, 53.3 mg/kg, respectively. The increasing rates were more significant in the first two years, and slowed down after that. Soil organic matter reached a suitable level after planting 3 years, and available phosphorus and potassium were reached a high level in at 3 years and 2 years after building the greenhouse. Soil nitrate accumulation increased with planting year in 0-2 m soil layer; and nearly 2/3 of nitrate were located in soil layer below 60 cm, indicating the high leaching of nitrate. Soil pH decreased, and soil electrical conductivity increased significantly with greenhouse ages. The annual surplus of nitrogen, phosphorus and potassium in greenhouses reached as high as 1396, 1516 and 1271 kg/hm2 in 5 years. There were significant correlation between the soil nutrient contents and nutrient surplus. Excessive fertilization is a big problem in local sunlight greenhouse, and decreasing nutrient inputs have great potential.⑶The cycling and balance of nitrogen and phosphorus during a year in 40 soalr greenhouses located in Yangling were investigated with material flow analysis method. The results showed that ①The inputs of nitrogen and phosphorus were 1637.5 and 668.3 kg/ha in greenhouse system, the outputs were 830.8 and 103.4 kg/ha respectively. Fruit harvest was the main way of nitrogen output, accounting for 38.5% of the total N output, followed by leaching. Plant residue was the main way of phosphorus output,accounted for 56.2% of the total P output. ②The surplus of nitrogen and phosphorus were very common in greenhouse system; soil nitrogen and phosphorus nutrient use rate were only 29.5% and 14.4%, pollution emission rate is as high as 61.5% and 62.6%. ③the loss nitrogen and phosphorus load in greenhouse system nutrient were as high as 1317.8 kg/ha and 629.6 kg/ha, making the greenhouse area as a high potential pollution area. Therefore, we recommend to reduce the inputs of nitrogen and phosphorus fertilizer, and recycle plant residues in greenhouse to increase nutrient utilization in greenhouse system, and reduce the harm of agricultural non-point source pollution.