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  • 1
    Electronic Resource
    Electronic Resource
    An evaluation of urea-rubber matrices as slow-release fertilizers (1990)
    Springer
    Nutrient cycling in agroecosystems 22 (1990), S. 63-70 
    Details
    ISSN: 1573-0867
    Keywords: Fertilizer ; slow-release ; rubber matrix ; urea ; residual
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The viability of a ‘urea-rubber matrix’ (URM) as a slow-release nitrogen fertilizer was assessed by field trials and incubation studies. Encapsulation of urea in the rubber matrix apparently prevented the inhibition of seed germination experienced at high temperatures (〉 20°C) following high urea applications. The release of urea from URM increased with temperature and was well described by a diffusion model which allowed for the temperature-dependence of both the diffusion coefficient in water and the saturated concentration of urea. Initial results suggest that the effect of varying the size of URM cuboids on both their release characteristics in moist soil and N-supply to plants is also reasonably well predicted by the diffusion model. In a ryegrass field trial over 24 weeks, the URM gave higher dry matter yields than either prilled urea or (NH4)2SO4 (following a single application at sowing) through efficient matching of nitrogen supply and crop demand.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01116180
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  • 2
    Electronic Resource
    Electronic Resource
    Urea-rubber matrices as slow-release fertilizers (1992)
    Springer
    Nutrient cycling in agroecosystems 31 (1992), S. 185-192 
    Details
    ISSN: 1573-0867
    Keywords: Fertilizer ; modelling ; rubber matrix ; slow release ; urea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of temperature and fertilizer particle size on urea release from a novel urea-rubber matrix (URM) composite was studied by incubation in 0.01 M CaCl2 solution. The release rate of urea from URM increased with increasing temperature and decreasing URM cuboid size which was well predicted by a diffusion-based model. However, the value of tortuosity factor, used in the model description, increased with increasing temperature. This may represent a genuine effect, due to changes in the morphology of the rubber pore walls, or may arise from deficiencies in the simulation model. Simulations of urea release from URM cuboids, given the predictable effects of both temperature and cuboid size, showed potential applications in a wide range of agricultural systems. As presented, the model is only strictly applicable to situations in which soil moisture is not limiting, such as paddy soils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01063292
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  • 3
    Electronic Resource
    Electronic Resource
    Urea-rubber matrices as slow-release fertilizers (1992)
    Springer
    Nutrient cycling in agroecosystems 32 (1992), S. 83-90 
    Details
    ISSN: 1573-0867
    Keywords: Fertilizer ; slow-release ; rubber matrix ; urea ; rice ; ammonia volatilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The efficacy of a prototype slow-release fertilizer, urea-rubber matrix (URM) was assessed under flooded rice conditions. URM cuboids of size 0.5 × 1.0 × 0.4 cm were applied in comparison with prilled urea at levels of 50, 130 and 200 kg N ha−1. URM was placed at the soil/solution interface in intimate association with rice seedlings whereas prilled urea was broadcast into the floodwater to simulate the normal application method of South East Asian farmers. URM cuboid sizes of 0.25 × 0.5 × 0.4 cm, 0.5 × 0.5 × 0.4 cm and 1.0 × 1.0 × 0.4 cm were similarly evaluated at a single rate of 130 kg N ha−1; a broadcast URM treatment was also included. Different methods of prilled urea application including deep placement and split application were also studied at a single rate of 130 kg N ha−1. It was found that the build-up of floodwater N (urea + NH 4 + ) from URM during the 13 days following application was almost negligible irrespective of level or method of application. This was thought to result in low losses of N through ammonia volatilization as shown by higher rice grain yields in comparison with prilled urea at all levels of application. Deep-placed urea gave a comparable grain yield to that of broadcast URM. There was no significant difference in grain yield between URM applied by placement and by broadcast, suggesting that URM can be effectively applied either in intimate association with rice seedlings or by broadcasting to the rice field before, or after, planting. An attempt to predict the release of urea from URM was made using a diffusion-based simulation model. It was found that the model underestimated the actual release of urea from URM within the rhizosphere, probably due to the extensive penetration by rice roots of the URM cuboids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01054397
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