Effects of cattle manure and mineral nitrogen fertilizer applications on nitrous oxide emission and nitrate leaching in a wetland cropping system in Zimbabwe
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The uncertainty in the contributions of N2O emissions from African regions to the global anthropogenic N2O emissions is largely due to the scarcity of data and low frequency of sampling in African tropical studies. The overall objective of this study was to determine the effect of cattle manure and mineral N fertilizer applications on N2O emissions and nitrate leaching in a wetland cropping system in Zimbabwe. Experimental treatments varying in rates of application, manure quality and timing of application were used as follows: Control; 100 kg N +15 Mg high N manure (1.36%N) ha-1; 200 kg N + 30 Mg high N manure ha-1; control; 15 Mg low (0.51%N) and high N manure ha-1; 30 Mg high and low N manure ha-1; control; 15 Mg high N manure; 30 Mg high N manure split into four applications of 3.75 and 7.5 Mg ha-1 per cropping event. A completely randomized block design was used in the experiments. Fluxes of N2O on soil were measured using static chamber techniques and gas chromatography. Nitrate leaching was measured using zero tension lysimeters for leachate collection. Study results have confirmed increased N2O emissions and nitrate leaching with increasing N fertilizer and manure applications to tomato and rape crops. Increasing the application rates of N fertilizer and cattle manure from 100 kg N + 15 Mg high N manure to 200 kg N + 30 Mg high N manure ha-1significantly (p<0.05) increased the loss of N by N2O emissions by 40% and 45% for the tomato and rape crops respectively. The same practice increased significantly the loss of N in nitrate leaching by 64% and 56% for the tomato and rape crops, respectively. The substitution of 15 and 30 Mg low N manure ha-1 with the same rates of high N manure increased N2O fluxes from wetland soil surface by 41% and 50%, respectively. When 15 and 30 Mg low N ha-1 manure were substituted with the same rates of high N manure total N lost through N2O emission increased by 59% and 31%, respectively. The proportion of applied N lost as N2O emission and nitrate leaching was higher in the rape crop than in the tomato crop. When 30 and 15 Mg of high N manure ha-1 were applied once in four cropping events N2O emissions were significantly higher than those recorded on plots that received split applications of 3.75 and 7.5 Mg ha-1 manure at least up to the second test crop. Thereafter N2O emissions on plots subjected to split applications of manure were higher or equal to those recorded in plots that received single basal applications of 15 and 30 Mg manure ha-1. When the applications rates of mineral N fertilize and manure were doubled, the loss of N in N2O emissions per unit dry matter yield decreased significantly (p<0.05) by 0.02 – 0.03 kg N2O-N/Mg of harvested dry matter. The loss of N from applied fertilizer per unit harvested dry matter yield decreases significantly with increasing harvested dry matter yield. The rates of nitrate N leaching losses of applied N in the current study were comparably similar with global average nitrate N leaching losses of 19% of applied. The percentage of N applied lost as N2O-N when N fertilizer and manure were applied was generally lower than the global default value of 1.25% of N applied. The most recent IPCC methodology for estimating direct N2O emission from applied fertilizer is based on emission data in temperate regions. These data are scant especially in sub-tropical regions of Africa. The current study is of important significance in providing a more complete data set from sub-tropical Africa to IPCC for incorporation into the predictive models for global estimations of N2O emissions
Additional Citation InformationMasaka, J. (2013). Effects of cattle manure and mineral nitrogen fertilizer applications on nitrous oxide emission and nitrate leaching in a wetland cropping system in Zimbabwe (Unpublished doctoral thesis). University of Zimbabwe.
SponsorMidlands State University through Research Board
SubjectBiogeochemistry of wetland soils
Mineral nitrogen fertilizer