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

Timing N application to enhance wheat grain yield - Mugendi et al.
was 1.2 tlha (Nyaki et ai., 1993). Nitrogen applied early may not be utilized by the plant but
rather lost through leaching and or run off if there are heavy rains immediately after sowing.
The relationship of timing N application to grain yield for wheat grown in the Northern Zone of
Tanzania is not well known.
Based on the above, a project was proposed with the following objectives:
1) To determine the effect of timing ofN fertilization on wheat gTain yield in northern Tanzania
2) To determine the optimum rate and timing of N feltilizer application to increase production
at minimal cost.
MATERIALS AND METHODS
A split plot experiment with 3 replications was tested at Rhotia and Mbulumbulu in Karatu
district, northern Tanzania for three years: 1997, 1998 and 1999. Three Tanzanian-developed
wheat cultivars namely Viii, Mbayuwayu, and Selian 87 representing maturity ranges i) 80-90
days, ii) 110-120, and iii) 120-130, respectively, were used in the trial. The 3 varieties were
broadcast at a seed rate of 150 kglha in 3 x 3m plots, and then incorporated into the soil by
rakes. Weeds were controlled by the application of Stomp immediately after seeding and
Buctril MC at mid-tillering.
Wheat cultivars used were: Al Viri, A2 Mbayuwayu, and A3 Selian 87. Rates of N application
were: BI 0 kglha, B2 30 kglha, B3 60 kglha, and B4 120 kglha. Times ofN application were: CI
All at seeding and C2All at mid-tilleling.
Data collected included: i) Number of wheat plants and weeds/m 2 at 30 days after emergence,
ii) biomass and iii) grain yield in t/ha. The data were subjected to statistical analyses using
MSTA TC computer software. Significant treatments were separated using the Least Significant
Difference (LSD) procedure.
RESULTS AND DISCUSSION
The wheat varieties tested at Rhotia, namely Viri, Mbayuwayu, and Selian 87, produced
statistically similar mean grain yields of 2.28, 2.37, and 2.28 tiha, respectively (Table 2). This
was not expected in a good environment where rainfall is not limiting like Karatu, especially in
1997 and 1998 when this site received uniform rainfall (Table 5). In such an environment,
Selian 87 is known to out yield Viri and Mbayuwayu because it is late maturing and utilizes the
extra moisture efficiently. However, in 1997, a wet season, Selian 87 tended to outyield both
Viri and Mbayuwayu. Higher grain yield was harvested in 1997 than in 1988 (Table 2).
Although enough moisture was received in 1998, the 3 varieties were infected by Barley
Yellow Dwarf Virus (BYD), which affected grain yield. The low grain yield in 1999 was
attributed to moisture stress before grain filling. Under moisture stress, Salisbury and Ross
(1990), found that abscisic acid, ABA, increased markedly in plant leaves and promoted root
growih at the expense of the photosynthetic factory. In addition, Reddy (1983) reported that
crop plants hastened maturity when moisture stress commenced after flowering leading to the
reduction of crop duration. These two factors of reduction of photosynthetic factory and crop
duration of wheat during the dry season probably had a significant effect of reducing the mean
grain yield of the varieties.
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