Effects of polymer materials on soil-crop nitrogen and phosphorus distribution and spring wheat yield
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Abstract
Polymer materials have broad potential applications for saving water and increasing crop yields in irrigated agricultural systems. However, little is known about how polymer on soil-wheat nitrogen and phosphorus. The purpose of this study is to evaluate the changes of humic acid (an alkali extract of cottonseed meal), modified polymer (a mixture of anionic polyacrylamide, polyvinyl alcohol, and manganese sulfate), and composite polymer (a 1:1 mixture of H and P) applied with drip irrigation on the content and storage of nitrogen and phosphorus in soil aggregates, and their effects on the nitrogen and phosphorus accumulation of plant organs and spring wheat yield. The results demonstrated that the addition of polymer materials had a great impact on the total nitrogen content of different fractions. Compared with control (CK), the humic acid treatment (H) significantly increased the total nitrogen content of >2, >1-2, >0.25-1, and ≤0.053 mm fractions in the >20-40 cm soil layer. The modified polymer (P) and composite polymer (HP) treatments significantly increased the total nitrogen content of >2, >1-2, ≤0.053 mm and >2, >0.25-1, ≤0.053 mm fractions in the surface soil (0-20 cm), respectively. In the total phosphorus content of different fractions, the H and P treatments significantly increased the total phosphorus content of >0.25-1 mm and >2 mm fractions in the top soil, respectively. Meanwhile, in the >20-40 cm soil layer, the total phosphorus content of >1-2 mm and >0.053-0.25 mm for H, the P treatments were totally different than that of CK treatment. In the nitrogen and phosphorus storages of aggregates, the H treatment mainly increased the total nitrogen and phosphorus storages of >0.25-1 mm fractions. The P treatment was beneficial to increase the total phosphorus storages of >1-2, >0.25-1, >0.053-0.25 and ≤0.053 mm fractions. Although polymer materials reduce the accumulation of nitrogen and phosphorus, while the dry weight of spring wheat stems, they have increased other plant organs (Flowering stage: leaf, and spike; Mature stage: leaf, husk and grain) in grains during maturity stage. Compared with CK, the accumulation of nitrogen and phosphorus in grains for the H and P treatments increased by 25.6% and 24.9%, 40.9% and 26.7% (P<0.05), respectively, while the grain yield increased by 19.7% and 12.6% (P<0.05), respectively. A Redundancy Analysis (RDA) was used to clarify the relationship between the storage of nitrogen and phosphorus in different fractions, and the accumulation of nitrogen and phosphorus, as well as the yield of spring wheat. The results showed that the nitrogen and phosphorus storages of >1-2 and >0.25-1 mm fractions were one of the main driving factors for the yield of spring wheat. Meanwhile, the humic acid and modified polymer materials can be used to promote the accumulation of nitrogen and phosphorus in the grain by increasing the nitrogen and phosphorus storage of >0.25-1 mm fractions and the total phosphorus storage of >1-2 mm fractions, respectively, thereby to increase spring wheat yield. The findings can be used to elucidate the action mechanism of polymer materials on soil nitrogen and phosphorus, and thereby to provide a more in-depth theoretical basis for local application and promotion of polymer materials.
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