The influence of gibberellic acid and sulfur fertilization rate on growth and S-use efficiency of mustard (Brassica juncea)

Abstract

Earlier research has shown that exogenous gibberellic acid (GA₃) application increases shoot growth, photosynthesis and soil nitrogen (N) utilisation in mustard (Brassica juncea L. Czern & Coss.). Mustard has a high sulfur (S) requirement. Its assimilatory pathway is well coordinated with N and dependent on photosynthesis. Thus, the higher photosynthate production and an efficient use of N with the use of GA₃ could result in an increase in S-use efficiency of the crop. The research was, therefore, carried out to study the effects of 10~μM GA₃ spray on specific leaf area, plant dry mass, leaf carbon dioxide exchange rate (CER), plant growth rate (PGR), relative growth rate (RGR), net assimilation rate (NAR) and S-use efficiency (SUE) of mustard treated with 0, 100 or 200 mg S kg⁻¹ soil levels. Plants treated with 100~mg S kg⁻¹ soil and receiving GA₃ treatment showed increased specific leaf area and dry mass accumulation compared to the control. At 0~mg S kg⁻¹ soil, N and S concentrations were reduced. They increased with increasing S supply. GA₃ application significantly increased N and S concentrations further. A two-fold increase in SUE in GA₃-treated plants at 100~mg S kg⁻¹ soil was noted in comparison to the control. SUE was not increased under excess S conditions beyond 100~mg S kg⁻¹ soil. The increase in SUE was through increase in the growth, CER and use efficiency of N by the crop due to GA₃ application.