A Study On The Mechanism And Effects Of A Super Absorbent Polymer Used In Agriculture On Plant Growth

The super absorbent polymers used in agriculture for water-saving and yield-increasing have been paid more and more attention to by people and as a result they have a broad applying prospect in agriculture. Aiming at a number of theoretic and technical problems during application of super absorbent, this thesis applied a super absorbent polymer named Sodium Polyacrylate for water-saving and yield-increasing in agriculture. Through potted planting, field and laboratory experiments, the effect of Sodium Polyacrylate on crop yield-increasing was tested and the yield-increasing mechanism was analyzed from effects of Sodium Polyacrylate on water-saving, fertilizer-keeping and soil texture-improving. The main conclusions are listed as follows:1. The growth and yield of cabbage were enhanced by Sodium Polyacrylate applied in the soil at a dosage of 0.2% by weight and the yield-increasing effect was more notable with the percentages of 99% in sandy soil and 71% in clay when fertilizers were used together. The Sodium Polyacrylate reduced the water used in the whole lifecycle of cabbage by 7% and 6% respectively in sandy soil and clay. The watering number was reduced by about 12% in both sandy soil and clay. WUE of cabbage planted in sandy soil and clay were increased by 44% and 42 respectively by Sodium Polyacrylate, which is even higher with the percentages of 117% and 84% when fertilizers were used together.2. The effects of Sodium Polyacrylate applied in the gully digged about 10cm in depth between rows of wheat on winter wheat were more notable than those of what splashed on the surface of the soil. The Sodium Polyacrylate applied in the gully could increase effectively tiller and growth of the wheat, and affect the kernel number in each wheat ear and 1000 kernel weight, and as a result increase the yield. The yield and WUE of winter wheat could be increased by 10.14% and 28.67% respectively when the and 100 kg/hm~2 N, P, K fertilizer are applied. The yield was increased by 11.24% by Sodium Polyacrylate applied in the gully at 20kg/hm~2 with an addition of 20mm irrigation during the filling in wheat. The effects of Sodium Polyacrylate used in winter wheat on growth and yield of the following maize were not noble.3. Water contentθand suction s were both fitted the modelθ=asb no matter whether the Sodium Polyacrylate was added in the sandy soil, silt and clay. The soil water retention increased with more polymer used and the effect on sandy soil were more notable than silt and clay. The dosage was suggested from 0.08% to 0.2% by weight, then 83.7% of the water kept by the polymer could be used by the crop.4. The saturated hydraulic conductivity (Ks) of sandy soil decreased with more Sodium Polyacrylate applied. The rate of wetting front advance and infiltration rate under certain ponded infiltration was significantly reduced by Sodium Polyacrylate , and as a result effectively reduced water in a sandy soil leaking to a deeper layer under the plough layer. Considering both the effects on water retention and infiltration capacity, it was suggested to add Sodium Polyacrylate to the sandy soil at concentrations ranging from 0.2 to 0.5%.5. The evaporation of Aeolian sandy soil, Loessial soil and Lou Soil decreased with more applied in soil. 10 days cumulative evaporation of Aeolian sandy soil, Loessial soil and Lou Soil was reduced by 59.89%, 48.92% and 55.81% respectively by Sodium Polyacrylate at 5 g·kg-1 soil. It is suggested to add Sodium Polyacrylate in the Aeolian sandy soil and Loessial soil ranging from 0.8 to 2 g·kg-1 soil and strictly about 2 g·kg-1 soil in the Lou soil when the effects of Sodium Polyacrylate on the soil water retention and evaporation are both considered. The time from saturated soil moisture content to wilting percentage of Aeolian sandy soil, Loessial soil and Lou soil was extended by 244.72%,251.11% and 36.31% respectively when Sodium Polyacrylate was applied at the suggested dosage.6. Loss of N fertilizer in the Aeolian sandy soil, Loessial soil and Lou Soil could be reduced by application of Sodium Polyacrylate and this effect was even more obvious as more Sodium Polyacrylate is applied. Nitrate and total nitrogen content in soil was increased while the ammonium nitrogen was not obviously affected. The effect of Sodium Polyacrylate on N fertilizer keeping was most obviously on Aeolian sandy soil then Loessial soil and Lou Soil. In the winter wheat field experiment, with the dosage of Sodium Polyacrylate applied in soil increased, productivity of Fertilizer-N first increases and then decreases. The yield was increased and the productivity of Fertilizer-N got the maximal value when Sodium Polyacrylate was applied at a dosage of 20kghm-2.7. Soil texture was improved by application of Sodium Polyacrylate. Content of macro-aggregates and aggregate water stability were increased while the aggregate deterioration rate and erodibility were decreased by addition of Sodium Polyacrylate. This effect was most obviously on Loessial soil, then Aeolian sandy soil and Lou Soil. The N fertilizer increased the aggregate deterioration rate and reduced the effects of Sodium Polyacrylate improving soil texture. This reduction on Sodium Polyacrylate of urea was less than ammonium, bicarbonate, ammonium nitrate and ammonium sulphate, so that urea should be used when N fertilizer be needed.