The Eleventh Regional Wheat Workshop For Eastern ... - Cimmyt

Agronomic and economic evaluation ofon-farm Nand P response - Amsal et at.
planted with a gross plot size of 4.8 x 5 m (= 24 m 2 ) in the Vertisol zone and 4 x 5 m (= 20
m 2 ) in the Nitisol zone.
Host fanners, according to their customary practices and using the traditional ox-plow
system, prepared the trial seedbeds. The BBF drainage system, using a 0.8 m wide raised bed
and a 0.4 m wide furrow, was superimposed at planting for all trials in the Vertisol zone to
facilitate drainage of excess surface water during the crop growing season. All P fertilizer
was applied at planting, while N fertilizer was split applied (Tilahun et al., 1996): one-third
ofN was applied at planting and the remainder was top-dressed at mid-tillering.
Host fanners selected sowing dates: all trials were sown from the latter half of June to the
first week of July across the two years. Immediately after surface broadcast application of the
basal N portion and all P fertilizer, a pre-weighed quantity of seeds of the bread wheat variety
"Kubsa" was broadcast sown at the rate of 150 kg ha- l , then soil-incorporated by constructing
BBFs in the Vertisol zone and by one pass of the local ox-plow in the Nitisol zone (i.e., as per
farmers' practice). The bread wheat variety "Kubsa". a semi-dwarf high-yielding variety
selected from CIMMYT gennplasm (= "Atilla"), was released in 1993 on a national scale.
Weeds were controlled by post-emer.gence spraying of 2,4-D at the rate of 1.5 I product ha- l
at 25 DAB and Puma S at the rate of 1.0 I product ha- l at 55 DAE in all trials.
Plant height and the number of productive spikes m- 2 were detennined for each treatment
prior to plot harvest. Numbers of kernels spike- l were detennined from 20 spikes sampled at
random from each plot. At physiological maturity, plants from a net plot size of 3 x 4 m were
hand-harvested close to the ground surface using sickles. The haryests were sun-dried in the
open air, weighed to detennine the above-ground biomass yield, then threshed and grain
yields were weighed for each treatment. Harvest index was detennined as the ratio of grain
yield to above-ground biomass yield and expressed as a percentage. Thousand-kernel weight
was detennined by weighing 1000 seeds randomly sampled from each plot yield. The number
of grains m- 2 was detennined as the product of the number of productive spikes m- 2 and seeds
spike-I.
Statistical and economic analysis. All data were subjected to combined analysis of variance
(ANOV A) using MSTATC microcomputer software. .
The 13 N by P interaction means for grain yield (GY) for both trial sets were fitted to the
following response surface by multiple regression analysis:
The coefficients thus derived were used to detennine economic optimum Nand P20S rates
according to the methodology of Jauregui and Sain (1992) for continuous economic analysis
of crop response to fertilizer. Specifically, for each nutrient an "r" value was calculated; the
economic optimum nutrient level was found by equating the partial derivatives of the
response surface to the respective "r" value, and solving for nutrient rate. For each nutrient,
"r" was detennined from the equation:
r = P F (1 + R)/(Pos - Cy)(1 - a)
where PF fertilizer price per kg of nutrient
R the minimum acceptable rate ofreturn (MARR): set at 1.0 (=100%)
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