Potential of Summer Legumes to Fix Nitrogen and Benefit Wheat Crop under Rainfed Condition
Titel:
Potential of Summer Legumes to Fix Nitrogen and Benefit Wheat Crop under Rainfed Condition
Auteur:
Rifat Hayat Safdar Ali
Verschenen in:
Journal of agronomy
Paginering:
Jaargang 3 (2004) nr. 4 pagina's 273-281
Jaar:
2004
Inhoud:
Rotational field experiments were conducted at University of Arid Agriculture, Rawalpindi Research Farm to investigate the residual effect of summer legume species in wheat-based cropping system in rainfed environment. Legumes species including Soybean (cultivar-NARC 1), Mungbean (NM 92), Mashbean (NARC 2) grown along with maize (Neelam) as reference crop were planted for N2-fixation determination during summer season of 1998 (July-October) with the aim of evaluating their biomass production and grain yields, nitrogen (N) and N2-fixation using xylem solute and natural 15N abundance techniques and the quantification of grain yield differences of succeeding wheat crop compared with a cereal-cereal rotation. During winter wheat crop, Var. Inqalab 91 was grown with 0 and 100 kg N ha-1 on the same plots previously having legumes. Cultivation of summer legume crops therefore, constitutes an alternative to traditional cropping practices of leaving the land fallow. Performance varied greatly between species. Legumes dry matter ranged from 7.46, 3.39 and 4.52 t ha-1 with soybean, mungbean and mashbean, respectively. Maize not fertilized with N produced 9.76 t ha-1 of dry matter compared with 13.56 t ha-1 when fertilized. Mean grain yields for three legumes were 1.68 (soybean), 0.82 (mungbean) and 1.83 t ha-1 (black gram). Maize not fertilized with N produced 4.35 t ha-1 of grains compared with 5.86 t ha-1 when fertilized. The comparison of %Pfix (proportion of plant N derived from N2-fixation) both (%Run) and (δ 15N) showed that the xylem solute and natural 15N abundance techniques have independent estimates of %Pfix. Consequently crop Nitrogen fixed ranged from 55-207 and 41-145 kg ha-1 by xylem solute and δ 15N techniques, respectively. Data were also subjected to simple regression analysis with Pfix and total N2-fixed as the dependent variables and shoot N, dry matter and grain yield as independent variables both for % RUN and δ 15N. Regression coefficient (r2) for Pfix of xylem solute were 0.45 (p<0.05) with shoot N as the independent variable and 0.63 with grain yield. For total N2-fixed, the regression coefficient was high at 0.87 using dry matter yield. When N2 fixation was calculated by δ 15N data, regression coefficient (r2) for Pfix were 0.21 and 0.59 with shoot N and grain yield, respectively. However, for total N2-fixed comparatively high value of regression coefficient (r2 = 0.80; p<0.05) was obtained with biomass yield. Both legume rotation and fertilizer N improved the biomass and grain yield of following wheat crop. For 0N wheat increase were 2.5 and 3.6% for wheat biomass, when the prior crops were soybean and mungbean and 7 and 14% for grain yield, respectively. The response of the wheat to fertilizer N, irrespective of prior crop, were large, ranging from 5 to 11%. The results highlight the need for thorough biological economic analysis of cropping option.
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