Office for Environmental Programs - Theses

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Subject: Agriculture × Start date: 2010 × End date: 2014 × Author: Ireland, Eric Addison ×

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    Release patterns of controlled release fertilisers and nitrogen use efficiency
    Ireland, Eric Addison ( 2012)
    Synthetic nitrogen fertilisers have enabled increasing crop yields to match world population growth, but losses of fertiliser nitrogen to the environment have significant environmental impacts, including eutrophication of coastal marine environments an nitrous oxide emissions. One way of reducing these environmental impacts while maintaining or increasing yields is to increase nitrogen use efficiency (NUE) of crops. Increasing NUE means that more of the fertiliser nitrogen applied to crops is taken up by plants, and ultimately made incorporated into food, and less is lost to the environment. Controlled release fertilisers (CRF) can be used to increase NUE, because by releasing nitrogen into the soil in a controlled way, they have the potential to match the supply of nitrogen to plant demand for nitrogen throughout the growth period. In order to achieve this result, the release rate of the CRF must match the plant demand for nitrogen. If the release rate is too fast, excess nitrogen in the soil after application may be lost due to leaching, ammonia volatilisation or denitrification before it can be taken up by the crop and if nitrogen is released too slowly, it may remain in the soil after crops are harvested, and be lost to the environment. In this study, the release rates of three different CRFs and granular urea were tested in a 70 day laboratory incubation in two sandy soils, and one clay soil. The CRFs tested were Environmentally Smart Nitrogen (a polymer coated urea), XCU polymer coated sulphur coated urea, and Optiset, a lipid coated urea. The polymer coated urea (PCU) had the slowest release rate in all three soils. Lettuces were then grown in a glasshouse for 56 days with either PCU, a single application of urea before transplanting, a split application of urea, or control with no nitrogen fertiliser applied. The lettuces that received a single application of N had lower NUE and fresh weight than those that received a split application of urea or PCU. Less nitrogen was leached from the PCU treated lettuces. These results suggest that a single application of PCU may be used to produces lettuces with similar NUE and fresh weight to a split application of urea, but with less nitrogen lost due to leaching.