Differences in Seasons and Rice Varieties Provide Opportunities for Improving Nitrogen Use Efficiency and Management in Irrigated Rice in Kenya
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Date
2021
Authors
Gweyi-Onyango, Joseph P
Ntinyari, Winnie
Ogollaegesa, Andrew
Mose, Richard
Njinju, Symon
Giweta, Mekonnen
Masso, Cargele
Journal Title
Journal ISSN
Volume Title
Publisher
IOP Publishing
Abstract
Apart from nitrogen (N) rates, N use efficiency (NUE) (yield N/total input N) is affected by
seasons, crop developmental stages, and varieties. Knowledge of how these factors affect NUE in
rice production in Kenya is limited. Therefore, field experiments were conducted with ‘low rates’ of
N (simulating farmers’ practices) of 0, 26, 52 and 78 kg N ha−1 with five varieties (MWUR1,
MWUR4, IRAT109, NERICA4 and NERICA10) and higher rates of N (125, 175, and
225 kg N ha−1
) simulating researchers’ doses with two lowland varieties (Basmati 370 and BW
196) and IR 72. Another experiment on NUE responses to sites, N rates and dose (split or full dose)
was undertaken with the IR97 variety. With the ‘low rate’, yields increased with incremental N rates
up to 52 Kg N ha−1
and declined (during cold periods, for some varieties). In this scenario, the N
agronomic efficiencies (AEN) declined with increasing N but depended on sites and seasons.
However, most AEN values were above 100, implying nutrient mining. In most cases (except at the
Mwea site), the N utilization efficiency (NUtE) ranged from 16 to 22 kg kg−1
and were not
significantly affected by sources and methods of N application. In all cases, an increase in N elicited
declining trends in NUtE. Moreover, N uptake efficiency ranged between 22 and 90 kg kg−1
without significant variation among varieties. For the ‘high N rates’, high biomass yield resulted in
higher grain yields in BW 196 and IR 72 but yield declined beyond 75 kg ha−1 N rates due to poor
grain filling, particularly when a cold period coincided with booting and grain filling. We conclude
that N rates, doses and rice varieties are key determinants of AEN and NUtE in contrasting rice
growing seasons in Kenya. Cropping seasons and rice varieties are therefore potential key
determinants of sustainable rice productivity and improved NUE in rice-based systems in the
studied regions of Kenya
Description
Article
Keywords
grain filling, temperature, nitrogen use efficiency, nitrogen agronomic efficiency, N-mining, N uptake and remobilization, policy Supplement
Citation
Gweyi-Onyango, J. P., Ntinyari, W., OgollaEgesa, A., Mose, R., Njinju, S., Giweta, M., & Masso, C. (2021). Differences in seasons and rice varieties provide opportunities for improving nitrogen use efficiency and management in irrigated rice in Kenya. Environmental Research Letters, 16(7), 075003.