A Comparative Evaluation of the Efficacy and Economic Analysis of Coated and Non-coated Nitrogen Application in Maize (Zea mays L.) at Seed-Co Research Station in Zimbabwe

Abstract

Maize (Zea mays L.) top-dressing in both smallholder and commercial production in Zimbabwe is carried out using uncoated nitrogen (N). A study was conducted for two consecutive seasons in 2015/2016 and 2016/2017 at Seed-Co’s Rattray Arnold Research Station and Stapleford Research Centre, Zimbabwe to determine the comparative performance on maize grain yield and nitrogen use efficiency of Polymer coated urea fertilisers against conventional ammonium nitrate (AN) and plain white urea fertilisers. The study also looked at the loss of fertiliser nitrogen via volatilisation and economic advantages of each top-dressing source of nitrogen to maize cropping in Zimbabwe. The top-dressing treatments were; zero N, 69 N kg/ha and 138 N kg/ha. A volatilisation experiment in the lab was carried out using AN Plain white urea, Agrotain coated urea, and NBPT coated urea. The field experiment was laid out as a randomised complete block design (RCBD) and was a 6 x 2 x 2 factorial experiment involving 3 factors. The growth attributes measured were, plant height, stem diameter, number of leaves, chlorophyll content, number of days to 50% tasselling, grain yield, and nitrogen use efficiency (NUE). The results showed that there was no significant difference (p>0.05) in Grain Yield (GY) and NUE between zero N top-dressed plots, half rate (69 kg N/ha) and full rate (138 kg N/ha) topdressed plots. This was attributed to high inherent nitrogen levels in the soil and not to the type of top-dressing fertiliser. Source of N was found to have no effect on chlorophyll levels in the leaf. Nitrogen losses through leaching from the same five top-dressing nitrogen sources were observed to be insignificant (p>0.05) and with no impact on both maize grain yield and NUE across soil depths of 15cm, 30cm and 45cm. The observed low leaching was attributed to high organic matter levels in the soil. Late top-dressing of N was observed to result in higher levels of residual N in the soil at the end of the season. This explains that maize plants also provided a sink for the applied mineral nitrogen and when it is missed during peak demand, there is higher residual N in the soil at the end of the season. Nitrogen volatilisation experiment results from the five top-dressing sources were ranked as follows in ascending order: NBPT urea< Black Urea® < White urea < Agrotain green/red urea < Ammonium nitrate. From the volatilisation experiment it was deduced that coated N delays the rate of N loss by volatilisation. A survey conducted to assess the adoption and cost effectiveness of coated nitrogen fertilisers on the market revealed that lack of product knowledge and related information on the new technologies is leading to very slow adoption and uptake of controlled release/stabilised N fertilisers. Maize farmers need more product information to adopt coated nitrogen fertilisers.