118
summer crops due to unpredictable growing conditions and poor extension services
provided by extension staff (FAO 1988 ), but fertilizer application at optimum rate
enhanced the crop yield by 50–129 % (Tandon 1980 ). Beside the low fertilizer input
in dryland regions than irrigated regions, the crop residues of dryland crops are used
as fodder by farmers, which further worsen the situation.
2.3 Water Scarcity
Water scarcity in dryland regions, and extreme weather variability are major factors
which affects the nutrients retention in soil, and their availability to the plants.
Presence of water in root zone is essential for the uptake of nutrients by plants. If the
soil water contents will be lower, the N mineralization (Table 2 ), and its uptake by
the plant will be lower. In dryland regions, water shortage prevails regularly due to
which the nutrients are not taken by the plants even they are present within the soil.
In summer rainfall areas in India, efforts have been made to improve the water use
efficiency. In a study, Kanwar and Mudhahar ( 1984 ) reported that the water use
efficiency of prepetition received was enhanced when N was applied to pearl millet
on an Alfisol in India. Fertilizer application to dryland soils enables the plants
extract to soil moisture from deeper soil layers due to deeper root penetration. In
dryland soils, soil moisture sometimes becomes a decisive factor for the crop
responses to applied fertilizers. In two independent studies in India, the rate of N to
which sorghum and wheat (Triticum aestivum L.) responded was completely depen-
dent on the amount of moisture stored in soil profile (Meelu et al. 1976 ; Umrani and
Patil 1983 ). In another study, application of N at the rate of 120 kg ha−^1 to wheat on
a clay loam soil with water storage capacity of 320 mm produced the same grain
yield as was obtained with same fertilizer level under irrigated conditions (FAO
1988 ).
Table 2 Impact of variable water contents on the mineralization of N at different temperatures
over time
Temperature
(°C)Time
(week)Amount of N mineralized (mg N kg−^1 ) at different water
content (%)
8 15 22 29
15 2 2.5 5.7 9.2 10.6
21 10.2 18.8 24.3 33.3
25 2 2.9 6.4 9.6 12.6
21 18.9 29.6 37.6 50.6
35 2 3.9 10.7 14.4 18.3
21 28.4 49.2 68.9 84.6Source: Li et al. ( 1995 )
A. Nawaz and M. Farooq