| The lush foliage of green manure can effectively reduce soil moisture evaporation from the surface,increase water infiltration,slow down the direct erosion of the surface,reduce the frequency of surface runoff and soil erosion,and have a good soil and water conservation benefits.At the same time,green manure can be incorporated into soil as a renewable biological fertilizer source,and its decomposition can release various nutrients such as nitrogen,phosphorus and potassium,which promote main crop growth and increase soil nutrients.With the increase in the use of chemical fertilizers and cost inputs,environmental and economic pressures have increased.At the same time,sustainable development of agriculture is increasingly valued for soil quality,so the rational cultivation and utilization of green manure have a great significance.Based on the goal of reducing the amount of fertilizer applied and increasing soil fertility,this study aims to explore the appropriate fertilization level,amount of green manure and the proportion of fertilizer reduction for different green manure,and improve the quality of land and yield for the application of green manure and providing stable technical support for construction of high and stable yield basic farmland;and providing scientific basis for further integration and optimization of key technologies for green manure cultivation and utilization in modern agriculture.In this paper,pot experiments were carried out,to study the effects of different nitrogen and phosphorus fertilizers on the growth of green manure and soil fertility;the effects of different application rate of leguminous green manure(Vicia villosa var.)on citrus seedlings and soil fertility;the effects of reducing the application of fertilizers on growth of citrus seedlings and soil fertility under the same amount of green manure,which provide theoretical basis and new ideas for improving the efficient use of green manure nutrients and promoting the sustainable development of green agricultural in China.The main results of the study are as follows:(1)With the increase of nitrogen application rate,the growth stages of different varieties were different,and the plant height,branch and biomass tended to increase.Compared with no nitrogen fertilizer,the germination,seedling emergence and branching stages of leguminous green manure were advanced by 1-2 days.The time of leguminous green manure from sowing to seedling emergence is relatively consistent,germination and seedling emergence of Medicago sativa L.is the earliest;Vicia villosa var.first in the branching stage,the first flowering stage and the peak flowering stage.The time of Medicago sativa L.,Trifolium repens L.,Brassica napus L.and Lolium perenne L from sowing to flowering is relatively long,reaching to 75-84 days.With the increase of nitrogen application rate,the height of the five green manures increased by2.57%-78.37%,and the number of tillers significantly increased by 7.91%-129.33%,and the fresh weight and dry weight of the flowering period increased by 1.66%-293.33%and 0.27%-273.43%,respectively.(2)With the increase of nitrogen application rate,the nutrient uptake of green manure increased significantly.The nutrient uptake of NPK and C were significantly increased by29.03%-444.45%,16.81%-268.74%,15.94%-340.88%and 1.42%-340.11%,respectively.Except Trifolium repens L.,nitrogen absorption of leguminous green manure was higher than that of cruciferous green manure Brassica napus L.and gramineous green manure Lolium perenne L.;the phosphorus absorption of leguminous green manure increased first and then decreased,at 60 mg/kg reached the maximum;the potassium absorption of non-leguminous green manure Brassica napus L.and Lolium perenne L.were higher than that of leguminous green manure.The difference in absorption uptake among different treatments is significant.Carbon absorption of Lolium perenne L.was the largest among different treatments.(3)With the increase of nitrogen application,soil nutrient changes different after green manure harvesting at flowering stages.Soil pH fluctuated after harvesting green manure at full flowering stage,but there was no significant difference among the treatments.Alkaline nitrogen and organic matter increased,but available phosphorus significantly decreased.Among them,available phosphorus of Lolium perenne L.decreased the most,reaching to 33.72%.Soil available potassium showed different characteristics,but there was no significant difference among different fertilization treatments of Vicia villosa var..Compared with control(no nitrogen fertilizer),Medicago sativa L.increased by 7.38%-12.75%,and the differences among Trifolium repens L.,Brassica napus L.and Lolium perenne L.treatments significantly decreased.(4)With the increase of phosphorus application rate,the growth stages of different varieties were different,and the plant height branch and biomass tended to increase.Compared with no phosphorus fertilizer,the germination,seedling emergence and branching of leguminous green manure were advanced by 1-3 days.The time from sowing to seedling emergence of leguminous green manure was relatively consistent,and Medicago sativa L.germinated and emerged the earliest,and Vicia villosa var.was the first in the branching,early flowering and full flowering stages.The time of Medicago sativa L.,Trifolium repens L.and Brassica napus L.Lolium perenne L from sowing to flowering is relatively long,reaching to 70-80 days.With the increase of phosphorus application rate,the height of the five green manures increased by 1.58%-24.62%,and the number of tillers significantly increased by 9.46%-60.24%,and the fresh weight and dry weight of the flowering period increased by 1.49%-38.42%and 1.19%-26.89%,respectively.(5)With the increase of phosphorus application rate,the absorption of NPK and C in green manure show an increasing trend,which increased by 0.08%-18.47%,2.12%-97.30%,0.90%-17.17%and 1.81%-34.19%,respectively.The absorption of nitrogen of different green manure is different at flowering stage.The absorption of nitrogen in green manure is comparatively higher than that of no phosphorus fertilizer green manure,which increased by 1.26%-29.56%.The phosphorus absorption of Trifolium repens L.was small,and at phosphorus application of 150 mg/kg reached the maximum,which increased by 33.10%,compared with the no fertilization treatment,and the carbon absorption in Lolium perenne L.was the largest.With the increase of phosphorus application,soil pH value,alkaline nitrogen and available potassium significantly decreased after harvesting green manure at full flowering stage,while available nitrogen and phosphorus significantly increased.Soil organic matter increased first and then decreased.(6)Through the study on growth and nutrient absorption and utilization of citrus seedlings under different application rates of Vicia villosa var.,the results showed that the growth of citrus seedlings could be promoted significantly when the application rates was 15000 kg/hm~2.The plant height,stem diameter,nitrogen,phosphorus and potassium absorption of citrus seedlings could reach to maximum,and the carbon absorption of citrus seedlings organs had no significant difference among treatments.Soil pH,available phosphorus and available potassium was increased after incorporated but alkaline nitrogen and organic matter decreased significantly.(7)With the increase of fertilizer application rate,when the application of the Vicia villosa var.is 15000 kg/hm~2,except for stem diameter largest at reducing the fertilizer application of 15%,the plant height and nutrient uptake of NPK on the citrus seedlings are all increased at reducing the fertilizer application of 30%.There was no significant difference in carbon absorption among treatments.With the increase of fertilizer application rate,soil pH,available phosphorus and available potassium showed an increasing trend,but alkaline nitrogen and organic matter significantly decreased.In summary,due to suitable local,high nutrient content,small amount of fertilization,and the lower consumption of soil fertility,Vicia villosa var.is priority selection,which is incorporated at the flowering stage and suitable nitrogen application rate at 60 mg/kg.Under the soil fertility in this experiment,Vicia villosa var.has better growth,maximum biomass,and the best nutrient uptake during the full flowering period of phosphorus application rate at 150 mg/kg.It is suitable to plant green manure in the range of 75-150 mg/kg.In the initial stage of green manure decomposed,it is necessary to consume nutrients.Green manure decomposed on the basis of single application of fertilizer can inhibit the growth of crops in a short period of time.Combined with the growth of citrus seedlings and the changes of soil nutrients,the amount of application is 15000 kg/hm~2,which is beneficial to crop growth.Reducing fertilizers application can significantly reduce soil fertility and inhibit the growth of citrus seedlings in a short period of time.If the turning time is increased,nutrients of green manure completely release.On the basis of application 15000 kg/hm~2 of green manure,reducing the application of15%-30%of the fertilizer can promote the growth of citrus seedlings,and increase nutrient absorption and soil fertility. |
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