Application of superabsorbent polymers in forestry and revegetation fields

Abstract

The amendment of soil with superabsorbent polymers (SAPs) has been gaining interest in agriculture and forestry, in both dry and semi-dry lands since the late 1970s. Here, we review studies on the characterization, application, and evaluation of SAPs in forestry and revegetation fields worldwide. SAPs usually absorb amounts of pure water several hundred times their dry weight; however, their absorption capacity decreases significantly for water containing salts and SAP expansion by water is restricted to the soil pore space. Until now, the experiments with SAPs have been mainly conducted on 1) root dipping of seedlings, 2) soil water holding capacity and drought tolerance of tree seedlings, 3) field application of SAPs to planting holes, and 4) gel seeding. The water-holding capacity of the soil increases with the amount of SAP added but the effects of the SAP on soil available water content and plant growth were more evident in sandy soils than in clayey soils. The application of SAP exhibited both positive and negative effects, depending on the soil texture and tree species. Some studies show that overuse of SAPs resulted in low seedling growth rates. The limitations of SAPs included the following: reduction in water holding capacity by combined use of fertilizers, short durability of SAP effects, and lack of cost evaluation. Further systematic studies are necessary to 1) develop suitable application methods, 2) identify applicable tree species by systematic studies in dry and semidry lands, and 3) improve the SAP products.