| Recently facility agriculture has been promoted countrywide as an important way to minimize the effects of natural disasters and achieve high production and efficiency of the off-season vegetable. However, the practice can have adverse effects on soil including low crop yield, secondary salinization, acidification, and nutrient imbalance because of the high multiple cropping index and fertilizer input in the process of facility vegetable cultivation. Among them, Soil secondary salinization is the most serious problem. Salts accumulated in surface soil can cause soil hardening, and nutrient imbalance which consequently can harm crop growth, reduce crop yield and quality, and decrease soil microbial divesity, eventually degrade overall soil environment, and endanger human health and ecological integrity. Therefore it is very important to characterize the status of soil secondary salinization in facility agriculture and develop the remediation technology for promoting the sustainable development of facility agriculture.This research focused on the typical facility vegetable greenhouse. With the planting age 0-3a,4-6a,7-10a and more than 10a in Shanghai suburban areas. The status of soil secondary salinization was surveyed and evaluated. Based on the results of the field samples and analyses, five potential restoration agents (manure, straw, furfural residue, chitosan, and bamboo charcoal) were selected from industrial and agricultural wastes and their effects on soil salt, major ions and rape biomass were assessed by using the adsorption test of restoration agent on soil soluble ions and pot culture experiments with single or combined restoration agents in the greenhouse. The followings are the major findings:1. The field survey results showed that facility vegetable production was centralized in Pudong, Qingpu, Fengxian, Jiading, and Jinshan district. In the greenhouse of these districts, the soil salt content was higher than that of open vegetable fields, and soil secondary salinization occurred in different degrees. The Soil salt content increased with the years of the planting and reached the peak about 6 year while the pH decreased with the years of the planting, reached a minimum about 7 years. The soil salt content reached the maximum about 3 years in the mode of continuous cropping solanaceous vegetables, and about5 years in the mode of continuous cropping leaves vegetables, respectively. Overall, the soil salt content under latter mode was higher than the former modes. 2. The results of restoration agent adsorption test on soil soluble ions showed that the treatments of manure, bamboo charcoal, and chitosan had good adsorption to soil salt,and the content of ions was reduced in different degrees. A good adsorption also obtained in the straw and furfural residue treatments when their dosages were 0.6,2.5g/g soil, respectively.3. The results of the impact of single restoration agent on secondary salinization soil by pot culture showed that the rape biomass increased with all of the 5 treatments. Among them, the manure treatment had the optimal effect. With the treatments of furfural residue, the rape yield increased when furfural residue was 55 t·hm-2 which was the second best only to the manure treatment. The Soil salt content reduced with the all 5 restoration agent treatments, and decreased most in the manure and straw treatment groups. The soil concentrations of Na+,Ca2+,Mg2+,K+,Cl-,NO3-, and SO42-lowered in the treatment groups of straw, bamboo charcoal and chitosan. The concentrations of Mg2+ and NO3- decreased and others increased in the treatment groups of manure and furfural residue. Both manure and straw were selected as the best restoration agents based on the restoration effects and the economy of five restoration agents. The optimal amount of these agents were 30,9 t·hm-2, respectively.4. The results of the effects of combined restoration agent on secondary salinization soil by pot culture showed that the soil salt content decreased and the rape biomass increased in the groups of different combinations of manure, straw, chitosan, furfural residue except the group of manure (45t·hm-2)+furfural residue (55 t·hm-2).Compared with the control group, soil concentrations of Na+,Ca2+,Mg2+,and K+ were not significantly different among the groups of furfural residue (55 t·hm-2)+1%chitosan solution(99 t·hm-2), manure(30 t·hm-2)+furfural residue (55 t·hm-2)+1% chitosan solution, and manure (45 t·hm-2)+furfural residue (55 t·hm-2).The concentrations declined substantially in other combined groups. SO42- concentration significantly increased in the groups of furfural residue combined with other restoration agents while Cl-, NO3-concentrations dropped in all of the combined groups. The group of manure (15 t·hm-2)+straw (3 t·hm-2) was selected as the best combination based on the restoration effects and economy of all groups comprehensively. |
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