Characteristics Of Nutrient And Heavy Metal Content,Risk Of Nitrogen And Phosphorus Leaching,and Control Measures In The Soil-scallion System In Luxi County,Yunnan Province

Luxi County,Honghe Prefecture,Yunnan Province is an important base for the cultivation of scallion in China.The cultivation of shallot has the characteristics of short growth cycle,high multiple cropping index and large amount of fertilizer application,which leads to the serious problem of nutrient loss in shallot planting land.However,the watering frequency,fertilization method and amount,soil nutrient loss and heavy metal characteristics of shallot planting in this area are still unclear.This paper takes the main production area of scallion in Luxi County,Yunnan Province as the research object,and uses field visits and questionnaires to investigate the fertilization mode,water and fertilizer management of scallion.The nutrient and heavy metal contents of soil-onion system were determined and evaluated in 28 onion planting soils and onion samples.Finally,the soil planted in Luxi County was used as the test soil to simulate the watering amount of Luxi County,and the indoor leaching test was carried out to study the risk of nitrogen and phosphorus loss in the soil planted in Luxi County.The three materials of sepiolite,biochar and zeolite were added to study their resistance to soil nitrogen and phosphorus loss.The main results are as follows :(1)According to the field visit survey,Luxi County scallion planting fertilizer,watering frequently.The growth period of shallot is roughly 40 ～ 60 days.The local farmers fertilize once every 10 ～ 15 days on average.46 % of the growers choose to apply75 ～ 100 kg / mu of compound fertilizer,and 18 % of the growers will apply more than100 kg / mu of balanced fertilizer.The planting of shallot is mainly based on sprinkler irrigation.The irrigation frequency is generally 1 ～ 2 times a day,about 15 ～ 25 minutes at a time,and the daily irrigation amount is 3 ～ 8 tons / mu.(2)The comprehensive soil fertility level of scallion planting in Luxi County is high,and the risk level of heavy metal pollution is low.The analysis of soil nutrient content of scallion planting found that the proportion of second-grade land with higher fertility level was 14.2 %,and the proportion of third-grade land with medium fertility level was 50 %.The soil fertility was generally at the upper-middle level.The Nemero comprehensive index method was used to evaluate the soil heavy metals in Luxi scallion planting land.It was found that 60.7 % of the soil samples were at a safe level,32.1 % of the soil samples were at the warning limit level,and only 3.5 % of the soil samples were at a mild pollution level.(3)Leaching test found that after 6 times of leaching,the total nitrogen content of the leaching solution of the high-fertility Allium fistulosum planting soil decreased to 19.98 mg / L.According to(GB3838-2002),the total nitrogen content of the leaching solution is10 times that of the five types of surface water bodies;the total phosphorus decreased to0.0217 mg / L,which was the fifth type of surface water,and the ammonia nitrogen decreased to 1.16 mg / L,which was the fourth type of surface water.The total nitrogen in the leachate of the medium-fertility scallion planting soil decreased to 14.76 mg / L,which was 7.3 times the lower limit of the five types of water bodies on the surface.The total phosphorus decreased to 0.0209 mg / L,which was the fifth type of surface water,and the ammonia nitrogen decreased to 0.96 mg / L,which was the third type of surface water.The total nitrogen in the leachate of the low-fertility scallion planting soil decreased to 14.33 mg / L,which was 7.1 times the lower limit of the five types of water bodies on the surface.The total phosphorus decreased to 0.0215 mg / L,which was the fifth type of surface water,and the ammonia nitrogen decreased to 0.91 mg / L,which was the third type of surface water.It can be seen that the risk of nitrogen and phosphorus loss in the onion planting soil in Luxi County is high.(4)Adding biochar,sepiolite and zeolite can effectively control the loss of nitrogen and phosphorus in the soil of Allium fistulosum planting area in Luxi County.After 6 times of leaching experiments,the application of 5 % weight ratio of biochar,sepiolite and zeolite treatment will lead to the total nitrogen concentration of soil leachate decreased by43.7 %,28.5 % and 40.6 % respectively,the concentration of ammonia nitrogen decreased by 47.1 %,19.5 % and 28.4 % respectively,and the concentration of total phosphorus decreased by 23.1 %,24.8 % and 18.8 % respectively.It can be seen that the three materials used have a good control effect on the loss of nitrogen and phosphorus in the soil planted with chives.Among them,the best control effect is biochar,and the most economic benefit is zeolite.In a word,there is a situation of excessive fertilization in the cultivation of Allium fistulosum in Luxi,Yunnan Province.The soil fertility is high,and frequent watering leads to a greater risk of nitrogen and phosphorus loss in the soil of Allium fistulosum cultivation.The addition of biochar,sepiolite,zeolite and other materials can effectively control the loss of soil nitrogen and phosphorus,and can be recommended for the prevention and control of soil nutrient loss in Luxi Allium fistulosum planting.