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Title: Boron Dynamics in Alkaline Calcareous Soils and its Availability under Wheat-Cotton Cropping System
Authors: NIAZ, ABID
Keywords: Applied Sciences
Agriculture & related technologies
Soil Science
Issue Date: 2010
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 1/3 rd 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 non- exploitation 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 three- year (2005-2008) study was initiated to determine the boron status of soils under wheat- cotton 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 wheat- cotton, 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 KH 2 PO 4 (exchangeable B), 0.02 M HNO 3 -H 2 O 2 (extractable B), 0.25 M NH 4 - 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 15experiments 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 -1 cotton and wheat. Whereas five B levels (0.00, 0.25, 0.50, 0.75 and 1.00 kg ha ) 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 non- significant 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. The 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.
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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