Response of Improved Rainfed Rice Varieties to Low Soil Nitrogen

Nitrogen is one of the major essential plant nutrients and a key input required for better crop yields
and therefore scarcity of nitrogen fertilizer has been a major constraint to rice production particularly in
developing countries. Low soil fertility prevalent in farmer’s fields has led to low rice yields and the
ever escalating fertilizer prices have made this important input unaffordable to most smallholder
farmers who have limited resources for purchasing the required inputs. There has been concerted
efforts to identify rice varieties that are tolerant to low soil nitrogen since varieties differ in their ability
to impact productivity and some varieties can perform well under low nitrogen input.The Mwea Upland
rice (MWUR) varieties have been bred under low fertilizer input environment while other authors have
indicated that the New Rice for Africa (NERICA) gives high yields under low input conditions. There is
therefore need to identify the superior rice varieties that are adaptable to low soil nitrogen levels.
Thus, the objective of this study was to investigate the effects of different rates of nitrogen fertilizer on
improved upland rice varieties and to identify the low input adaptable varieties. Field studies were
conducted at Alupe in Western Kenya under rainfed upland conditions between August 2012 and April
2013. The experimental layout was split plot factorial in a Randomized Complete Block Design with
three replicates. The main plot treatments were four rates of nitrogen fertilizer levels which were; 0
(control), 40, 80 and 120 kg ha-1 applied as calcium ammonium nitrate (26% N) in two equal splits; 21
days after sowing (DAS) and at panicle initiation (46 DAS). Sub-plots consisted of four MWUR
varieties namely MWUR 1, MWUR 2, MWUR 3, MWUR 4; and four NERICA varieties namely
NERICA 1, NERICA 4, NERICA 10 and NERICA 11. The parameters measured included plant height,
tiller number, filled grain ratio percentage and yield components. In the study, nitrogen treatment
showed significant effect on plant growth and the measured parameters increased significantly with
increase in nitrogen level. MWUR varieties studied were more adaptable to low nitrogen conditions as
compared to NERICA varieties. The NERICA varieties recorded higher yield at high nitrogen levels as
compared to MWUR varieties. However, NERICA 4 gave higher yield as compared to other NERICA
varieties regardless of the nitrogen level. Results from our study suggest that MWUR 1 and 2 and
NERICA 4 were more tolerant to low nitrogen as compared to MWUR 3 and 4 and NERICA 1, 10 and
11, because of higher height, more tiller number, higher filled grain ratio percentage and higher yield
component as compared to the other studied varieties and may be suitable for soils low in nitrogen.