Plant response and environmental aspects as affected by rate and pattern of nitrogen release from controlled release N fertilizers

Abstract

The effect of N release rate and pattern on plant growth, N uptake and losses was assessed by comparing five urea- based controlled release nitrogen (CRN) fertilizers significantly differing in release mechanisms and characteristics and split applied conventional urea. Profiles of N release in water and in an incubation test in a sandy loam were compared to results of a pot experiment in which N losses (4 leachings) and N uptake (4 cuttings) by rye grass were determined.

CRN exerting high initial release in water (″burst effect″) caused losses of up to 45-50% of the applied N, mainly in the first leaching. This inflicted in some cases damage to young seedlings. The release rate of N from some of the CRN was significantly reduced after 40 to 60% of the N was released (″tailing effect″). Consequently, growth rate and N uptake by plants was reduced in comparison to other treatments. Fertilizers having a linear or sigmoidal release pattern and with almost no ″tailing″ at the final release stage produced highest yields and N uptake with minimal losses of N by leaching.

Using CRNs which well match the pattern of plant demand resulted in total uptake of 70 to 80% of the applied N, while losses by leaching ranged between 1 to 15%. On the other hand, the use of fertilizers which poorly fitted the pattern of plant demand resulted in uptake of only 20 to 30% of the applied N and the losses due to leaching exceeded the amount taken up by the plant! Split application of urea in a manner which minimized leaching losses resulted in uptake of 35 to 55% of the applied N.

Results clearly indicate that increasing N use efficiency and lowering environmental damage by using CRN can be critically affected by the ability to match release characteristics of a CRN to the pattern of N demand of the crop.