Agrotechniques for mitigating water stress in vegetable cowpea (Vigna unguiculata (L.) Walp.)

Abstract

Water stress is one of the major abiotic stresses that limits crop production. Vegetable cowpea is an important non season bound crop in Kerala and water scarcity limits its area under cultivation during summer season. Research reports indicate that water stress in crop plants can be mitigated by foliar spray of plant growth regulators, seed hardening mulching, antitranspirant sprays and nutrient management. However, research works in this line in Kerala are meagre. Hence a study was taken up to develop a package for mitigating water stress in summer vegetable cowpea by assessing the effect of above practices on the growth and yield of the crop. Field experiments were conducted during the summer season (Jan-Mar) of 2014 and 2015, using the variety Kashi Kanchan. There were three experiments during the first year to evaluate the effect of (1) exogenous application of plant growth regulators (PGRs), (2) seed priming, antitranspirant sprays and soil moisture conservation practices, and (3) nutrient management practices for mitigating water stress in vegetable cowpea. The best treatments from each of the first year experiments were selected and their effects independently and in combinations were evaluated in an experiment during the second year of study. The first experiment was done to evaluate the effect of various plant growth regulators in mitigating water stress in vegetable cowpea. Among the treatments, farmers practice (irrigation at 2 days interval) recorded the highest growth and yield and absolute control the lowest. Among plant growth regulators, salicylic acid 2 per cent and NAA 40 pm recorded higher growth and yield by way of their favourable influence on mitigating water stress. The second experiment was conducted to evaluate the effect of seed priming, mulching, and antitranspirant sprays in mitigating water stress. The results showed that, among seed primers, , seed hardening with 0.5 per cent NaCI recorded better growth and yield of cowpea compared to that with 2 per cent CaCl2 and per cent KH2PO4 due to the comparatively better efficacy of sodium chloride in equipping the cowpea plants for drought tolerance. Mulching with polythene and plant residues were equally effective in recording better plant growth and yield due to their favourable influence on soil moisture availability. Among anitranspirants, foliar spray of lime water as 2 per cent Ca(OH)2 during the water stress imposed period resulted in better growth and yield of cowpea plants due to increased albedo. The third experiment was conducted to evaluate the effect of various nutrient management practices in mitigating water stress. The results revealed that among nutrient managements practices, foliar spray of 2 per cent DAP+I Per Cent KCL, 0.5 per cent ZnSO4 and seed treatment with PGPR mix I+ rhizobium were better in attaining higher growth and yield under water stress. In the second year, the best treatment from each of the first year experiments were selected and their independent and combinations were evaluated. In general, plant growth was higher higher in all mulched treatments, either alone or in combinations, NaCL+PRM+ (PGPR mix 1+rhhizobium)+ Zinc sulphate recorded the highest growth yield income ,net profit (Rs.2,03,389/-) and B:C ratio ( 4.1) which was even higher than farmers practice. Plant residue mulching alone also recorded higher yield and B:C ratio than farmers practice which showed the significant influence of mulching in mitigating water stress. Among the independent treatment, foliar spray of either Zinc sulphate or salicylic acid was found better compared to others in terms of growth and yield of vegetable cowpea.