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In order to improve the utilization rate of nitrogen fertilizer and reduce the environmental pollution risk of the nitrogen accumulation in the vegetable field, this study was carried out in the summer leisure period of the greenhouse vegetable production. This experiment designed different planting density treatments in 2017 and 2018, i.e. for catch waxy corn, 3300 plants/667m2 (WCD1), 5000 plants/667m2 (WCD2), 6600 plants/667m2 (WCD3), for forage sweet sorghum, 4500 plants /667m2 (FSS4), 7000 plants/667m2 (FSS5), 9000 plants/667m2 (FSS6) in 2017; and for catch waxy corn, 4500 plants/667m2 (WCDI), 7000 plants/667m2 (WCDII), 9000 plants/667m2(WCDIII), for forage sweet sorghum, 7000 plants/667m2 (FSSIV), 10000 plants/667m2 (FSSV), 14000 plants/667m2 (FSSVI) in 2018. The results showed that the biomass and nitrogen absorption of the two catch crops began to improve and then decreased with the increase of planting density. The nitrogen absorption amount of the catch waxy corn and forage sweet sorghum was 22.36~28.68 kg/667m2,21.67~24.39 kg/667m2, respectively. Different planting density of catch waxy corn and forage sweet sorghum could significantly reduce the total nitrogen content of 0~30cm soil layer and the nitrate nitrogen content of 0~90cm soil layer, for catch waxy corn and forage sweet sorghum, the reduction rate of total nitrogen content in 0~30cm soil layer was 9.6%~27.0%, 5.7%~23.5%, the reduction rate of nitrate nitrogen content reached 50.0%~90.8%, 80.1%~96.4%, respectively, which effectively controlled the nitrate nitrogen leaching to soil deep layer. Planting catch crops could increase soil urease activity, regulate soil nitrogen transformation. Compared with other treatments, WCDII and FSSV treatment can reduce the initial urease activity and soil nitrate nitrogen content of next crops, which is consistent with the nutrient requirements of broccoli in the early stage of growth. These catch crops planting could reduce the nitrogen environmental risk in the greenhouse soil. Finally, the study proposed that the suitable planting density of catch waxy corn and forage sweet sorghum planted was 6600~7000 plants/667m2, and 9000~10000 plants/667m2, respectively, in the greenhouse summer leisure period. It is more advantageous to improve soil nitrogen absorption and reduce soil nitrogen environmental risks for catch waxy corn.

In this experiment, the effects of different types of conditioners and their application on the absorption and transformation of phosphorus in high phosphorus soils in facilities were investigated to improve the environmental problems of protected farmland caused by phosphorus accumulation. Waxy corn was used as a test crop, and five conditioners such as humic acid, biochar, bentonite, alum, and dephosphorized gypsum were used as test materials for potting experiments. The experiment set 10 treatments, namely T1(Blank control), T2(Humic acid), T3(Biochar), T4(Bentonite), T5(Alum), T6 (Dephosphorized gypsum), T7(Biochar-bentonite-alum), T8(Humic acid-biochar-alum),T9(Humic acidbiochar- bentonite-alum),T10(Humic acid-bentonite-biochar-alum-dephosphorized gypsum). Based on the analysis of the results of the three crops, except that the first crop was not significant, the biomass and phosphorus absorption of waxy corn of T2 was the highest in the second crop, and T10 was the most effective treatment in the third crop. The soil available phosphorus content of T8 was the lowest in the second crop and that of T10 was the lowest in the third crop, which were 12.01% and 12.75% lower than the control. The soil water-soluble phosphorus content of T4 was the lowest in the second crop, which was 41.84% lower than the control, and that of T8 was the lowest in the third crop, which was 26.62% lower than the control. According to the results of the three crops, the ratio of the total phosphorus content of the inorganic phosphorus in the third crop of each treatment was increasing compared with the first crop. The soil phosphorus was transformed from organic phosphorus to inorganic phosphorus. The ratio of total phosphorus content of organic phosphorus of T6, T9, T10 was larger than other treatments, which slowed down the conversion of phosphorus to available form. The ratio of Ca8-P in the inorganic phosphorus was the highest, reaching about 50% to 60%. From the results and analysis, T2 and T10 were beneficial to the absorption of soil phosphorus by waxy corn, T8 and T10 were beneficial to slow down the conversion of phosphorus to the effective state, reduce the potential risk of phosphorus environment, improve the phosphorus accumulation environmental issues in greenhouse farmland.

With the goal of improving N fertilizer management to maximize soil organic carbon (SOC) storage and minimize N losses in high-intensity cropping system, a 6-years greenhouse vegetable experiment was conducted from 2004 to 2010 in Shouguang, northern China. Treatment tested the effects of organic manure and N fertilizer on SOC, total N (TN) pool and annual apparent N losses. The results demonstrated that SOC and TN concentrations in the 0-10cm soil layer decreased significantly without organic manure and mineral N applications, primarily because of the decomposition of stable C. Increasing C inputs through wheat straw and chicken manure incorporation couldn't increase SOC pools over the 4 year duration of the experiment. In contrast to the organic manure treatment, the SOC and TN pools were not increased with the combination of organic manure and N fertilizer. However, the soil labile carbon fractions increased significantly when both chicken manure and N fertilizer were applied together. Additionally, lower optimized N fertilizer inputs did not decrease SOC and TN accumulation compared with conventional N applications. Despite the annual apparent N losses for the optimized N treatment were significantly lower than that for the conventional N treatment, the unchanged SOC over the past 6 years might limit N storage in the soil and more surplus N were lost to the environment. Consequently, optimized N fertilizer inputs according to root-zone N management did not influence the accumulation of SOC and TN in soil; but beneficial in reducing apparent N losses. N fertilizer management in a greenhouse cropping system should not only identify how to reduce N fertilizer input but should also be more attentive to improving soil fertility with better management of organic manure.

Specific knowledge about the characteristics of coastal land use along the sea−land direction helps to better understand the spatial heterogeneity of coastal land use, which could offer scientific support for rational land management and the sustainable development of the coastal zone. However, the traditional methods including buffering or the regional method are hard to extract detailed spatial structure and location correlations of coastal land use along the sea−land direction. Therefore, we developed a model, called sequence−based clustering of coastal land use pattern (SCCLUP), to mine the coastal land use sequence patterns (CLUSPs) along the sea−land direction. As a case study in the major coastal zone of Bohai Bay and the Yellow River Delta from 1990 to 2010, we found that: (1) The land use showed a sequential distribution along the sea−land direction. And the land use closed to shoreline and inland boundary had relative stable sequential location along the sea−land direction. However, the middle land uses had dynamic sequential locations that led to multiple CLUSPs; (2) due to the increasing percent of construction land, the artificial level of CLUSPs was continuously increasing and new CLUSPs tended to distribute around port areas. Different CLUSPs with similar land use sequential relationships tended to have similar land use structure along the sea−land direction; (3) the land uses sequential location along the sea−land direction revealed the actual distance of land use to the shoreline and had a tight correlation with environmental factors (salinity, water, and landform). The land use with large increasing and wide adaptivity (like construction land) had a large impact on the changes of CLUSPs in the study area. Therefore, strong control should be provided for the excessive expansion of land use like construction land to limit the over changes in land use pattern along the sea−land direction. Additionally, the spatial heterogeneity of land use along the sea−land direction should be considered to a better understanding of anthropic impacts on the coastal zone.