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Nitrogen is the nutrient demanded in largest quantities by crops and most expensive in the process of industrial production. Although it is abundant in the atmosphere but crops cannot directly utilize the elemental form available in the air. Next to plant photosynthesis, biological nitrogen fixation is probably the most important biochemical process for life on earth. Biological nitrogen fixation occurs mainly through symbiotic association of legumes and some woody species with certain N2-fixing micro organisms that convert elemental nitrogen into ammonia. Inclusion of legumes in cropping system can play an increasingly important role to maintain soil fertility and sustain crop production. The ability of legumes to fix atmospheric nitrogen, their nodulated roots and plant residues left after harvesting represent a valuable source of organic N. Annual crop legumes, grown in rotation with cereal crops, can improve yields of the cereals and contribute to the total N pool in soil. Reported yield responses to previous legume crops are mainly in the range of 50-80% increases over yields in cereal-cereal sequence. Benefits of legumes have also been attributed to control of cereal diseases and insect pests and improvements in soil structure. Legumes can increase the efficiency with which water is used. Pothwar Plateau consists of more than one million hectare of northern Punjab, Pakistan. Being rain fed tract, it contributes significantly to agriculture. Rainfall is erratic and varies greatly from 1000 mm in the north-east to the 250 mm in south-west part of the region. The tract lies at 330.380 Latitude (N) and 73.00 Longitude (E). More than seventy percent of annual precipitation falls in the summer months. Major crops grown in this area are wheat, mustard, chickpea in winter and maize, sorghum, ground nut, mung and mash beans in summer season. The soils of Pothwar plateau are low in fertility especially in nitrogen, phosphorus and organic matter. Moreover, the recent trend for growing continuous cereals on all arable lands has further depleted the nutrients in the soils. With the use of expensive inorganic fertilizers, the cost of crop production has substantially increased. It is, therefore, important to promote economically viable and environment friendly interventions for sustainable agriculture in rain fed farming system of Pothwar. Keeping in view the beneficial effects of legume-cereal rotation, field experiments were conducted on mung bean (Vigna radiata) and mash bean (Vigna mungo) during summer 2002 and 2003 followed by wheat in each year at two different locations of Pothwar, at the Research Farm of University of Arid Agriculture, Rawa1pindi (UAAR) and farmer's field in Chakwal district, to quantify N fixation by mung bean and mash bean under P fertilization and inoculation using the xylem sap technique and to see the impact of legume-wheat sequence on water use efficiency (WUE), grain and N yields of the succeeding wheat compared with wheat-wheat sequence. Cultivation of summer legume crops, therefore, also offered an alternative to traditional cropping practices of leaving the land fallow. Non-legume sorghum was also sown along with legumes. Biomass yield of mung and mash beans ranged from 3.02, 2.95, 2.90 and 2.96 t ha-1 fertilized with and without P, respectively. Mean grain yield of mash bean fertilized with 80 kg P ha-1 was 1.04 t ha-1, 13 % higher over mash bean without P. Proportion of nitrogen derived through N2-fixation (% Pfix) in mash bean was 50, 11 % higher when compared with mung bean under P fertilization. Application of phosphorus to mash bean increased N2-fixation by 21 % as compared to mung bean fertilized with P. N2-fixation at UAAR site, was 41 % higher as compared to Chakwal site. N2-fixation in summer 2003, 49 kg ha-1, was 161% higher than that of summer 2002. The WUE on N2-fixation basis was 25 and 16 % higher in mash and mung beans fertilized with P over beans without P. The WUE on grain basis of mash bean, 1.75 kg ha-1 mm-1, was 41 % higher than of mung bean fertilized with P. Beans increased soil P by 6 %, Soil TOC by 16 %, Soil NO3-N by 26 % and soil water contents by 12 % over non-legume sorghum. Legume-cereal rotation increased succeeding wheat biomass and grain yield by 18 and 25 %, respectively over cereal-cereal sequence. WUE on grain basis of wheat was 8.90 kg ha-1 mm-1 11 % higher in the plots which were previously under mash bean fertilized with P as compared to non-legume sorghum. It is concluded that N2 fixation capacity of mung and mash beans was enhanced by application of phosphorus fertilization. Both beans fertilized with P increased the fertility of soil at both locations. Legume-cereal sequence also enhanced biomass and grain yield as well as WUE of subsequent wheat.

Item Type:Thesis (PhD)
Uncontrolled Keywords:Legume-Cereal, Cropping System, Biological Nitrogen Fixation, Mung Bean (Vigna Radiata), Mash Bean (Vigna Mungo), Cereal Yield,
Subjects:Agriculture & Veterinary Sciences(a) > Agriculture(a1)
ID Code:360
Deposited By:Mr Ghulam Murtaza
Deposited On:04 Aug 2006
Last Modified:04 Oct 2007 21:00

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