BIOMASS, NITROGEN, SULFUR, AND PHOSPHORUS CONTENTS OF BEANS GROWN IN LIMED SOIL IN RESPONSE TO FOLIAR APPLICATION OF HNO3 OR H2SO4 MISTS

Abstract

Bean plants (Phaseolus vulgaris L.) were subjected to simulated acid mist treatments (pH 4.5, 3.0, 2.3) in the greenhouse. Solutions containing either HNO3 or H2SO4 were applied as mists over a period of 31 days. The growth medium had a pHKCl of 7.9 and a calcium (Ca) content of 18.5 mg g−1. Plants were sampled at flowering and at ripening, for determination of length, fresh and dry weights of different plant organs, and number of nodules. The plant samples were analyzed for nitrogen (N), sulfur (S), and phosphorus (P) content. A significant reduction of stem growth was recorded as a result of the treatment. Some of the plants had interveinal chlorosis, indicating mild iron (Fe) or manganese (Mn) deficiency caused by the high soil pH. The lowest leaflet dry weight was 86% of the control at a dry matter content of 90% of the control. A reduction in shoot:root dry mass ratio was detected. Pod dry weight was not affected. High increases in leaflet N (145%) or S (204%) content were found, which were roughly proportional to the respective treatment levels of HNO3 or H2SO4. Phosphorus content and N:P ratio of leaflets responded to treatment levels and chemical composition of treatment solutions. The root S content was affected only slightly. Nodules were more sensitive to HNO3 treatment, which at pH 2.3 reduced the number of large nodules to 14% of the control at flowering. At ripening of the pods, the effect of treatments on nodules was less pronounced. H2SO4 treatment also reduced the nodule numbers at higher acidities of mist. Nodule numbers at different treatment levels covaried in all variants with stem height growth, shoot:root dry mass ratio and P content in pods. In HNO3 treated plants, the numbers of root nodules changed inversely to the S content in leaflets. It was concluded that an increase in S content in the plants was less than an increase in N content. The hypothesis that H2SO4 mist causes more disturbances in bean plants than HNO3 mist was not confirmed by the current experiments.