Bio-amelioration of alkali soils through agroforestry systems in central Indo-Gangetic plains of India

A long-term field study was initiated during 1995 at Central Soil Salinity Research Institute, Regional Research Station, Lucknow （26047＇58＂ N and 80°46＇24＂ E） to analyze the effect of agroforestry systems on amelioration of alkali soils. Three agroforestry systems （pas- toral, silvipastoral and silvicultural） were compared with the control where no agroforestry system was introduced. Tree-based silvicultural and silvipastoral systems were characterized by tree species Prosopis juliflora and Acacia nilotica along with grass species Leptochloafusca, Panicum maximum, Trifolium alexandrium and Chloris gayana. Growth of ten-year-old Prosopis juliflora and Acacia nilotica planted in combi- nation with grasses was significantly higher over the silviculture system with the same species. Tree biomass yields of P. juliflora （77.20 t·ha-1） and A. nilotica （63.20 t·ha-1） planted under silvipastoral system were significantly higher than the sole plantation of （64.50 t·ha-1 and 52.75 t·ha-1）. Fodder yield under the pastoral system was significantly higher than the silvipastoral system during initial years but it was at par with that of silvipastoral systems after eight years of plantation. The microbial biomass carbon in the soils of silvipastoral systems was significantly higher than in soils under sole plantation of trees and control systems. The Prosopis-based silvipastoral system proved more effective in reduc- ing soil pH, displacing Na＋ from the exchange complex, increasing or- ganic carbon and available N, P and K. Improvement in soil physical properties such as bulk density, porosity, soil moisture and infiltration rate was higher in the Prosopis-based silvipastoral system than in the silviculture system or control On the basis of biomass production and improvement in soil health due to tree ＋ grass systems, silvipastoral agroforestry system could be adopted for sustainable reclamation ofhighly alkali soils.

Biological improvement of saline alkali soil reference system:A review

This work presents a reference system overview to improve the efficiency of biological improvement of saline-alkali soil developed during the last thirty years, ranging from connotation, general methods and species, soil desalination, soil structure, soil organic content, microbial flora, enzyme activity, yield and economic benefits. The reference system presented is divided into three main groups: suitable varieties, suitable cultivation measures, and a comprehensive evaluation system.There has been a lot of research on biological improvement of saline alkali soil, but these studies are very fragmented and lack a comprehensive standard system. Also, there is a lack of practical significance, particularly with regard to optimal species, densities and times of sowing for particular regions. On the other hand, the corresponding cultivation measure is very important. Therefore, a reference system plays an important role to the effect of biological improvement of saline alkali soil.

Chao HUANG,Main Factors Affecting the Improving Efficiency of Gypsum for Solonetzic Soil

In order to more efficiently utilize gypsum to improve meadow alkali soil slightly salinized by soda and sulfate chloride, a total of 27 treatments were de- signed from the perspectives of field capacity, alkalinity, alkaline salt content, optimal irrigation, gypsum conversion, gypsum and soil treatment and improvement depth. The ions on the obtained filtrate were analyzed in terms of salts. The improving ef- ficiency of gypsum for meadow alkali soil was analyzed through comparing the con- tents of soluble salts in pre-improvement and post-improvement soil by reasoning and calculation. The results showed that, （1） the dissolved amount and conversion amount of gypsum were increased, and the soil alkalinity was decreased corre- spondingly with the increased irrigation amount. However, after reaching a certain extent, the linear relationships became unobvious gradually. Therefore, the irrigation amount should be arranged reasonably for different treatment. （2） Compared with those at low temperature, the dissolved amount of gypsum at high temperature was increased by 1.47-1.50 times, the release amount of exchangeable sodium was in- creased by 2.98-4.70 times, and the release amount of exchangeable magnesium was increased by 2.07-2.90 times. In overall, the improving efficiency of gypsum in summer was better. However, gypsum had two shortcomings in summer. First, a large amount of gypsum leaked away. Second, a large amount of exchangeable magnesium, along with exchangeable sodium, was substituted by gypsum. （3） Compared with the other two treatments, treatment B （mixing gypsum and top 20- cm soil） showed the best improving efficiency, and it was characterized by stepwise dealkalization from top to down. In addition, mixing gypsum and topsoil is more practical in the production.