Polyacrylic acid (PAA) has high water absorbency but poor salt resistance. Humic acid (HA) extracted from lignite was introduced into the cross-linked copolymer systems of AA to improve the water absorbency and salt-tolerance. A polyacrylic acid-potassium humate (PAA-KHA) coated ammonium dihydrogen phosphate (ADP) fertilizer with water-preserving, salt-resistant and slow-release properties was prepared. The main properties of HA extracted from lignite oxidized by H2O2 were studied. Furthermore, the synthesis process, water absorbency of PAA-KHA in deionized water and in NaCl solution, morphologies of PAA-KHA, and the slow-release performance of the fertilizer (ADP@PAA-KHA) were investigated. The results showed PAA-KHA had a layered interpenetrating network, which can provide sufficient storage space for water and nutrients. The salty water absorbency of PAA-KHA increased by about 3 times compared to PAA. Both the PO43− and NH4+ cumulative release of ADP@PAA-KHA with a coating rate of 10% in deionized water, were less than 20% within 24 h, and were 55.71% and 28.04% after the 15th day, respectively. The weight change of ADP@PAA-KHA before and after absorbing water was about 53 times in deionized water and about 4 times in 1 wt% of NaCl salty water. The results show that ADP@PAA-KHA has excellent properties of water retention, salt resistance and slow-release. This will efficiently improve the utilization of fertilizer and reduce the irrigation water consumption at the same time.

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To improve the utilization of stover and fertilizer and also save water resources, a degradable slow-release fertilizer of corn stover cellulose graft poly (acrylic acid-potassium humate) (CSC-g-P(AA-KHA)) was prepared using corn stover cellulose (CSC), acrylic acid (AA) and potassium humate (KHA) by aqueous solution polymerization. Characterization of CSC-g-P(AA-KHA) with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) techniques provided evidence for the successful preparation. The product prepared exhibited excellent water absorbency (792.89 gÁg À1 and 72.69 gÁg À1 in deionized water and 0.9 wt% NaCl solution, respectively) and enhanced soil's capacity of water holding and water retention. After 5 cycles, the water absorptivities of CSC-g-P(AA-KHA) in deionized water and 0.9 wt% NaCl solution were 51.71% and 49.97% of their initial water absorption, respectively. The degradation rate of CSC-g-P(AA-KHA) was 32.02% after 50 days. Soil column leaching test and pot experiment demonstrated the slow-release effect and plant growth promotion of CSC-g-P(AA-KHA). CSC-g-P(AA-KHA) showed desirable application potential in agriculture and is expected to become a functional fertilizer that integrates water absorbing, water-holding and slow-release properties.