Keywords (Extracted from title, table of contents and
abstract of thesis)
System, Cereal, Calcareous, Crop,
Boron, Determine, Water, Under, Dynamics, Fractionation, Alkaline,
Tillering, Cropping, Availability, Soils, Cotton |
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Abstract
Wheat (Triticum
aestivum L.) is the world’s leading cereal crop and is unanimously
consumed as staple food product of almost hundred percent Pakistani
nationals as well as about 1/3rd population of the world. Cotton (Gossypium
hirsutum L.) is an important cash crop of Pakistan but the yields of
wheat and cotton in Pakistan have been stagnated throughout the
preceding decade due to improper fertilizer management and
nonexploitation of micronutrients specially boron. Boron (B) is
extraordinary amongst the microelements in that an extremely
diminutive amount is required for ordinary growth and maturity of
plants, and simply somewhat greater B concentrations are toxic. A
threeyear (2005-2008) study was initiated to determine the boron
status of soils under wheatcotton system and also to assess the
relationship between soil B and physico-chemical properties of
soils. B content present in canal and tubewell waters being used by
wheatcotton,were also assessed. The responses of cotton and wheat
crops to foliar and soil applied B were also studied under field
conditions. Almost all the soils were calcareous in nature (92 %
area), alkaline in reaction (83 % area had pH > 8) and 100 % area
had OM < 1 %. In case of soil B content, 82 % soils were deficient
in B (0.10 to 0.45 μg g-1), 15 % were adequate (0.46 to 0.55 μg g-1)
and only three samples were sufficient (0.56- 0.91 μg g-1). More B
was observed in the fine textured soils (28 % area). Low B
concentrations were observed in wheat and cotton plants. The average
B concentrations during 2006 and 2007 in wheat leaves were 8.86 and
4.41 mg kg-1, and in cotton 37.78 and 15.83 mg kg-1. Mean B content
in canal water was more during monsoon season (0.14±0.10 mg L-1) as
compared to that during winter season (20±0.13 mg L-1),
respectively. Whereas, B concentration was more in tubewell waters
as compared to that in canal waters. B fractionation study revealed
that the highest mean plant available B(0.32±0.12 mg kg-1) was
obtained by hot water extraction followed by 0.05M HCl (0.31±0.12 mg
kg-1), and 1:2 water extraction whereas the lowest B concentration
was extracted by 0.005M DTPA. Total soil B content of all the soils
varied from 15.61 to 152.80 mg kg-1 and it was further fractionated
by using 0.05 M HCl (readily soluble B), 0.05 M KH2PO4 (exchangeable
B), 0.02 M HNO3-H2O2 (extractable B), 0.25 M NH4-oxalate extractable
B and the residual B. The highest mean B fraction was the residual
fraction (70.50 mg kg-1) whereas the lowest was the water soluble B
(0.33 mg kg-1). Field experiments were conducted at three different
textured soils (loam, sandy clay loam and silt loam). Ten B
treatments were applied to soil (0.00, 0.25, 0.50, 0.75, 1.00, 1.25,
1.50, 1.75, 2.00 and 3.00 kg B ha-1 at sowing along with recommended
NPK fertilizers for cotton and wheat. Whereas five B levels (0.00,
0.25, 0.50, 0.75 and 1.00 kg ha-1) were used for foliar application
in three replications in RCBD, while all other recommended nutrients
for cotton and wheat were applied. Foliar sprays were performed on
cotton before flowering, at flowering and at boll formation stages
while on wheat before tillering, at booting and at milking stages. B
application as soil and foliar sprays significantly increased the
number of bolls, boll weight, lint, seed cotton, dry matter yield,
lint percent, leaf B concentration and total B uptake. Foliar use of
B (0.50 kg B ha-1) increased the seed cotton yield by 25.60 % over
control on loamy soil followed by that on silt loam soil (23.80 %),
however during the next year (2007), seed cotton yield mildly
decreased compared to first year at the same B application level of
0.50 kg B ha-1 but it remained significantly higher than control by
8 and 21.50 % at loam and silt loam soil(23.80 %), respectively.
Likewise, wheat crop significantly responded to B application both
as soil and foliar in terms of grain and straw yields, number of
grains spike-1, 1000- grain weight, plant height, plant B
concentration and total B uptake while it had nonsignificant effects
on tillering and protein content. B application improved the grain
yield by around 6, 9.60 and 6 % at B application levels of 0.50,
0.75 and 1 kg ha-1, respectively. Finally, the residual or
carry-over study revealed significant responses of wheat crop to
residual B applied to previous cotton crop. Residual B significantly
improved the grain and straw yields, number of grains spike-1,
1000-grain weight, plant height, plant B concentration and total B
uptake and protein content of wheat. he highest and the lowest
protein content of 14.54 and 11.17 % were obtained with residual B
levels of 1.50 and 3 kg ha-1, respectively.
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