EFFECT OF DIFFERENT LEVELS OF SULPHUR AND PHOSPHORUS APPLICATION ON NITROGEN FIXATION AND YIELD OF CHICKPEA (Cicer arietinum L.)

Abstract

In Pakistan, work regarding crop response to sulphur application is limited to oilseeds and their oil contents only. Research work regarding integrated use of phosphorus (P) and sulphur (S) and their role in legume’s nitrogen fixation and nutrient uptake is very rare. Interactive effect of P and S on crop yield may be synergistic or antagonistic depending upon initial soil fertility status, levels of nutrients applied and test crop used. Therefore, present study was conducted to assess the effect of S and P application on seed yield, nitrogen (N2) fixation and nutrient uptake by chickpea crop under rainfed conditions of northern Punjab, Pakistan. Field experiments were conducted with Chickpea (Cicer arietinum L.) at Chakwal (32.5° N latitude, 72.4° E longitude) and Talagang (32.5° N latitude, 72.2° E longitude) during 2006-07 and 2007-08. The trials were carried out in RCBD having split split plot arrangement with P rates in main plots, S sources in subplots and S rates in sub sub plots. There were eighteen treatments comprising of different combinations of P levels (0, 40, 80 kg ha-1), S sources [gypsum and ammonium sulphate (AS)] and S levels (0, 15, 30 kg ha-1). Effect of P and S application was significant on N2 fixation and seed yield of chickpea. Phosphorus application had non significant effect on percent nitrogen derived from air (%Ndfa) while that of S application had significant effect resulting in increase in %Ndfa up to 6 percent. Application of P and S resulted in significant increase in seed yield up to 34 and 13 percent, respectively over control. Macronutrients uptake such as N, P and S in both straw and grain was significantly affected by sole as well as combined application of phosphorus and sulphur. Two S sources also differed significantly with higher uptake recorded with AS than gypsum. Application of S resulted in increased uptake of micronutrients such as zinc (Zn), copper (Cu), iron (Fe) and manganese (Mn) in both straw and grain. Similar results were also recorded for P with the exception that higher level of P application (80 kg P2O5 ha-1) resulted in decrease in Zn uptake in both grain and straw. Soil analysis after crop harvest revealed that application of P caused an increase in available P level up to 37 percent over control while that of S application resulted in reduction up to 10 percent. Reduction in soil S content up to 3 percent due to P application and an increase up to 30 percent was recorded because of S application. Sulphur status of gypsum treated plots was higher than that of ammonium sulphate. Higher value cost ratio (VCR) and marginal rate of return (MRR) was recorded for gypsum than ammonium sulphate. In case of combined application of P and S, maximum VCR (6.92) and MRR (9.50) were recorded for P1L1 (40 kg P2O5 and 15 kg S ha-1). Treatment P2L2 (80 kg P2O5 and 30 kg S ha-1) had negative MRR which shows that this fertilizer combination is not profitable. The study concludes that P application should be accompanied with S for pulses. This will lead to increase in fertility status of our soils resulting from more efficient N2 fixation. It will not only improve the quality of produce but will also lead to sustainability of soil resources. Gypsum is more economical S source than ammonium sulphate.