| The accumulation of nitrogen and phosphorus in vegetable fields of intensive greenhouse had been increasing,which had led to the degradation of greenhouse soil quality and increased environmental risks of nitrogen and phosphorus.This study was carried out to reduce the accumulation of nitrogen and phosphorus in greenhouse soils.Fresh waxy corn and forage sweet sorghum with large biomass in a short period of time and deep root system were selected as test materials during the greenhouse vegetable field leisure period.Three different planting densities were designed and field trials were conducted for two years.The six treatments were designed in film uncovering greenhouse vegetable field in 2018,which were waxy corn 67,500(WCD1),105,000(WCD2),135,000(WCD3)plants/hm2 and forage sweet sorghum 105,000(FSS1),150,000(FSS2),210,000(FSS3)plants/hm2;Fallow soil(FS),waxy corn 67,500(WCDⅠ),105,000(WCDⅡ),135,000(WCDⅢ)10,000 plants/hm2 and forage sweet sorghum 105,000(FSSⅣ),150,000(FSSⅤ),210,000(FSS VI)plants/hm2 in film uncovering greenhouse vegetable field and idle treatment(FS),105,000(FSS I),150,000(FSS II),210,000(FSS III),262,500(FSS IV)plants/hm2 in unpeeled membrane greenhouse vegetable field were designed in 2019.The effects of different treatments on the growth,nitrogen and phosphorus absorption of catch crops,changes in soil nitrogen and phosphorus content in greenhouse,soil urease and phosphatase activities,and soil nitrogen and phosphorus content in the early stages of crop growth were studied.The main results are as follows:(1)The increase of two kinds of catch crops planting density could promote the increase of plant height,but could inhibit the increase of stem thickness,and had no significant effect on chlorophyll.The biomass and nitrogen and phosphorus absorption of two kinds of catch crops in film uncovering greenhouse vegetable field both increased and then decreased as the planting density increased.The planting densities of waxy corn and forage sweet sorghum were 105,000 and 150,000 plants/hm2 respectively,they had the highest biomass and nitrogen and phosphorus absorption.Nitrogen and phosphorus absorption of catch waxy corn was 227.48~335.18 kg/hm2,65.74~128.80 kg/hm2,nitrogen and phosphorus absorption was mainly concentrated in the above ground,accounting for 93.3% and 92.5% of the total nitrogen and phosphorus absorption,respectively;Nitrogen and phosphorus absorption of forage sweet sorghum was 280.82~365.70 kg/hm2,95.24~150.23 kg/hm2,nitrogen and phosphorus absorption was also concentrated in the above ground,accounting for 89.8% and 87.7% of the total nitrogen and phosphorus absorption,respectively.The increase of planting density of forage sweet sorghum in unpeeled membrane greenhouse vegetable field could significantly increase the total biomass,but could reduce the root biomass of the plants.FSSⅡ and FSSⅣ treatments had higher biomass and nitrogen absorption,nitrogen absorption was 232.74kg/hm2,258.40kg/hm2,respectively and there was no significant difference.The phosphorus absorption of each treatment was 62.96~69.36kg/hm2,and there was no significant difference.(2)Planting catch crops could effectively reduce the total nitrogen and total phosphorus content of surface soil in film uncovering greenhouse vegetable field.The reduction rates of catch waxy corn were 21.4%、11.0%,and the reduction rates of forage sweet sorghum were 21.3%,5.0%.Unpeeled membrane greenhouse vegetable field for leisure in summer and planting forage sweet sorghum could significantly reduce the total nitrogen content of the soil surface,and the total nitrogen content of FSSⅡ,FSSⅢ,FSSⅣ treatment was significantly lower than that of FS treatment,and it was lower than the base sample19.5%~ 32.1%.Each treatment could also reduce the total phosphorus content in the surface layer of the soil.Among them,FSSⅢ and FSSⅣ treatments were significantly lower than the basic samples and FS treatment,the reduction rates were 12.6% and 12.8% respectively.Nitrate nitrogen and water-soluble phosphorus leached severely in each soil layer during the leisure period in film uncovering greenhouse vegetable field.Planting catch crops could significantly reduce the content of nitrate nitrogen in 0~30 cm and 30~60 cm soil layers,reducing 54.0%~90.5%,38.0%~80.4% by waxy corn by,and reducing 80.1%~90.3%,46.7%~81.2% by forage sweet sorghum.When planting densities of waxy corn were 105,000,135,000 plants/hm2 and planting densities of forage sweet sorghum were 105,000,150,000 plants/hm2,they could also significantly reduce the nitrate nitrogen content of 60~90cm soil layer.The content of nitrate nitrogen in 0~30,30~60,60~90cm soil layers of uncovered FS treatments increased significantly compared with the base samples,increasing by 225.0%,27.5%,and 19.2% respectively.Catch treatments increased by-0.8% ~ 93.4%,-32.6% ~ 94.7%,-36.1% ~ 36.8%,among which FSSⅡ treatment had the best effect on reducing nitrate nitrogen in each soil layer,followed by FSSⅠ treatment.Compared with FS treatment,FSSⅡ,FSSⅢ,and FSSⅣ treatments could reduce the available phosphorus content in the lower layer of the greenhouse soil by 30~60,60~90cm,and the reduction rates were 8.1%~80.1%,30.5%~55.1%,respectively.The reduction rates of water-soluble phosphorus content were-9.4%~49.5%,45.7%~80.9%.Planting catch crops in film uncovering greenhouse vegetable field could effectively reduce and control the Ca2-P content in the soil and promote phosphorus conversion.The leisure period of uncovering plastic film greenhouse vegetable field,could increase the content of soil Al-P,Fe-P,O-P,and could significantly reduce the content of Ca10-P.Planting catch crops could reduce Al-P,Fe-P,and O-P content,and FSSⅠ,FSSⅡ,and FSSⅢ treatments could increase Ca8-P content,which were beneficial to activating soil insoluble phosphorus.Planting catch crops could reduce the nitrogen supply capacity in the early growth stage of the following crops,and reduce the risk of nitrate nitrogen leaching of the greenhouse soil layers in the early stages of the following crops.Forage sweet sorghum could better control the water-soluble phosphorus content of each soil layer in the early stage of broccoli growth.(4)Compared with basic samples,planting catch crops could increase soil p H,and each treatment of forage sweet sorghum was significantly higher than that of FS treatment.Planting catch crops could effectively reduce the total amount of water-soluble salts in the greenhouse soil,and could reduce the total amount of water-soluble salts in the early stage of broccoli growth,WCD1,WCD2,WCD3,FSS4,FSS5,FSSⅤ,and FSS Ⅵ treatments significantly reduced the total amount of water-soluble salts in the greenhouse soil.Planting catch crops could increase soil microbial biomass carbon and DOC content,promote soil microbial reproduction and activities,and helped to improvement of soil quality.Among them,WCDⅡ,WCDⅢ,FSSIV,and FSSⅤ treatments were more obvious.(5)Nitrogen uptake of catch crops with leisure crops during the leisure period of vegetable greenhouse in summer accounted for 34.2%~49.7% of the annual nitrogen absorption of vegetables,and phosphorus absorption accounted for 30.0%~69.8% of the annual vegetable phosphorus absorption,It was important to reduce the nitrogen and phosphorus content in greenhouse soil.Planting catch crops could reduce or control the accumulation of nitrogen and phosphorus in greenhouse soil and reduce the environmental risk of nitrogen and phosphorus in in greenhouse soil.Looking at the multi-layered factors such as biomass,nitrogen and phosphorus absorption of crop,soil nitrogen and phosphorus,and other nutrient changes,when the greenhouse vegetable field was uncovered in summer,the planting densities of waxy corn and forage sweet sorghum were suitable for planting density of 105,000 and 150,000 plants/hm2 respectively.Among them,planting forage sweet sorghum was more beneficial for absorbing soil nitrogen and phosphorus and reducing the environmental risk of nitrogen and phosphorus in the greenhouse soil.The suitable planting density of sweet sorghum was 150,000 plants/hm2 in uncovering plastic film greenhouse vegetable field. |
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