Effects of Nitrogen Levels on Yield and Nitrogen Utilization Efficiencies of Two Rice Varieties in Kirinyaga County, Kenya
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Date
2018
Authors
Gweyi-Onyango, Joseph P
Journal Title
Journal ISSN
Volume Title
Publisher
Horticultural Association of Kenya
Abstract
Nitrogen is one of the most limiting elements in crop production and this is even worse in
the tropics where the farmers do not have the capacity to purchase the inputs. Ammonium
and urea forms of nitrogen have traditionally been applied in paddy rice. Despite the
anaerobic conditions expected in flooded rice, conversion of ammonium to nitrate has been
reported. Nitrate easily gets leached and lost. The other loss pathway is volatilization,
leading to emissions of ammonia gas. There is need for judicious application of N to ensure
proper utilization without incurring the losses. This can be assessed by determination of
nitrogen use efficiencies. The current study evaluated the utilization efficiencies of two rice
varieties (Nerica 4 and Nerica 10) supplied with four rates of nitrogen in form of urea. The
experiment was laid in Randomized Complete Block Design (RCBD) with split plot
arrangements, where two varieties represented the main plot while the nitrogen rates
constituted the sub-plots. The experiment was replicated three times. The growth
parameters determined were plant height, panicle length, shoot dry weight, root dry
weight, Harvest index and grain weight. The grain and straw nitrogen contents were
determined by Kjeldahl method and the following utilization efficiencies were computed:
Nitrogen Use Efficiencies (NUE), Nitrogen Agronomic Efficiency (NAE), Nitrogen
Harvesting Index and Nitrogen partitioning in grain and straw. Analysis of variance was
performed using Statistical Analysis System version 9.00. Means were separated using least
significance difference at a significance level of 5%. Associations between variables were
determined by regression analyses. The results revealed significant differences in shoot and
root dry weights, grain weight and plant height with Nerica 4 being superior in these
characters compared to Nerica 10. The NHIs were not affected by nitrogen rates in both
varieties though all of them were generally high (more than 0.6). The NAE ranged between
23-25% which is a fairly good indicators of better N utilization. The NUE ranged between
25-158, with majority being above 100 which is also an indication of low soil nitrogen.
Moreso, the partitioning of the N to the grain was threefold or more in the grain compared
to the straw. The association between N rates and grain yields were positive. Whereas the
association was polynomial for Nerica 4, it was linear for Nerica 10. We conclude that more
N can still be applied to Nerica 10 for increased yield since the N levels supplied were still
sub-optimal. For Nerica 4 there could have been other factors such as low temperatures
that contributed to low yields.
Description
Article
Keywords
nitrogen partitioning, remobilization, N mining, N export, nitrogen agronomic efficiency
Citation
Gweyi-Onyango, J. P. (2018). Effects of nitrogen levels on yield and nitrogen utilization efficiencies of two rice varieties in Kirinyaga County, Kenya. African Journal of Horticultural Science, 14, 23-34.