Water holding capacity and nutrient retention with bamboo sawdust regenerated super absorbent polymers

Water for irrigation is a critical factor for plant growth in mountainous commercial forests. To solve this water deficiency one effective way would be application of super absorbent polymers (SAPs) that could be produced from wood processing residues. In this study two SAPs, bamboo fiber grafted with potassium acrylate (No.2) and bamboo fiber grafted with acryl amide (No.4), regenerated from bamboo sawdust were compared with commercial potassium polyacrylate (S) to determine the water-holding capacity (WHC) in three types of water (deionized water, tap water, and distilled water) and four fertilizer solutions (potassium sulfate, ammonium dihydrogen phosphate, compound fertilizer, and urea) with five gradient concentrations (0.5‰, 1.0‰, 2.0‰, 4.0‰ and 8.0‰), as well as the WHC and nutrients protection in soils with or without fertilizers with same dosage (mass ratio of SAP to soil are 1:200). Also, effects of five dosages with a mass ratio of No.4 to soil being 1:100, 1:200, 1:400, 1:600, and 1:800, were designed to determine WHC and nutrient protection in soils with and without fertilizers. Results showed that the water absorption rate in the three types of water and four types of fertilizer solutions was highest with No.4(P S > No.2. WHC was positively related to SAP dosage and greatly affected by the solution concentration from ionic fertilizers of potassium sulfate, ammonium dihydrogen phosphate, and compound fertilizer but not by urea, the non-ionic fertilizer. Also the highest WHC with SAP No.4, especially the treatment with highest dosage (mass ratio of SAP:soil=1:100) resulted in the greatest loss of ammonium-N, nitrate-N, and potassium when the leaching water volume exceeded the WHC of the soil. In conclusion, SAP No.4 exhibited the greatest WHC and nutrient protection with a recommended dosage of 0.50% of the SAPs based on a dry soil mass (mass ratio of SAP:soil=1:200), but should avoid fertilizing with maximum precipitation > 40 mm to minimize leaching.