Development And Performance Evaluation Of Rubber Tree Water Sustained Release Fertilizer

Rubber planting area and dry rubber output in Hainan account for about50%of rubber planting area and dry rubber output nationwide. In recent years, relevant reports show that soil fetility of rubber plantation in Hainan declines year by year, which leads to serious restriction of increase production of rubber. With the tropical monsoon climate, Hainan has high and concentrated rainfalls; due to strong weathering, low cation exchange capacity and base saturation, and strong permeability of latosol, strong nutrient leaching loss, low utilization rate of fertilizer and serious fertilizer loss occur. Moreover, given the spatiotemporal differences regarding rainfall in Hainan, spring drought often happens, thus synchronization of fertilizer and water during the growth season of rubber trees can not be reached.In this paper, a new type of water-retentive sustained release fertilizer is developed by recombining fertilizer with water-retentive materials via techniques of mixing granulation and chemical polymerization, and its relevant properties and simulated application effect in latosol are tested. It aims to provide references for development of water-retentive sustained release fertilizers that are suitable to be popularized and applied in rubber production, so as to increase the utilization rate of fertilizer in latosol areas by exerting the synergistic effect of water and fertilizer, and improve the situation in which water and fertilizer are out of sync in rubber production in Hainan. Preliminary results are as follows:1. The new water-retentive sustained release nitrogen fertilizer (WSRNF) developed by chemical polymerization reaction with acrylic acid and urea as its raw material has good water-absorbing capability, water-retentive capability and repeatability in water absorption. Its water absorption rate and repeated water absorption rate in tap water are respectively167.17g·g-land137.52g·g-l; when in leaching liquors of latosol with water-soil ratios of1:5,1:10and1:20, its water absorption rates can respectively reach up to62.60%,73.54%and86.97%of that in tap water, with faster imbibing rate; it also has good water retention capacity under conditions at the room temperature,40?and60?. The chemical mechanism through which WSRNF has the effects of water absorption, water retention and sustained release of nutrients are expounded via FTIR analysis. TG-DTA analysis verifies that the equilibrium moisture content contained in the sample after full water absorption and swelling of WSRNF is99.43%, in which free and freezable water account for98.47%, while bound water accounts only0.96%. Free and freezable water can be used for growth of plants. By adding a small amount of WSRNF, the maximum water retention rate of latosol can be significantly improved, the evaporation rate of water in latosol can be reduced and the water use efficiency can be increased. With increase in application amount of WSRNF, the maximum water retention rate of latosol increases gradually. When WSRNF application amounts are0,0.5%,1and2%, maximum water retention rates of latosol are39.74%,63.46%,70.63%and79.42%, respectively. WSRNF has good sustained release performance in lotosol; during the soil-column leaching of latosol, accumulated release of nitrogen increases with increase of leaching times, and on the28th day after7times of leaching, accumulated release rate of nitrogen is94.35%.2. The new water-retentive sustained release compound fertilizers:A, B and C that are developed by adding three different water-retentive materials have good sustained-release effect for nutrients. Among the three fertilizers, C has the best sustained-release effect for nutrients, B takes the second place and A is the poorest among them. The three kinds of new water-retentive sustained release compound fertilizers not only have good sustained-release effect in latosol, but also can effectively improve its water-retentive capacity. The lifting effect of these three sustained release fertilizers on the maximum water retention rate of latosol and their inhibitory effect on evaporation rate of water in latosol enhance with increase in their application amounts, and C has the best effect, B takes the second place and A is the poorest among them.Simulated experimental results show that the new water-retentive sustained release fertilizer for rubber trees developed in this experiment has good water-retentive and sustained-release effects, but its practical application effect remains to be verified via field experiment.