Impact of the Bangshi river water quality on rice yield

Abstract

Impact of the Bangshi River water quality on irrigated soil, plant growth and yield of BRRI Dhan 29 was investigated during the 2007-2008 boro season. The study was conducted by selecting two study sites, one is pollution affected Kulla union (Site-lor polluted site) at the downstream part and the other is pollution free Sombhag union (Site-II or control site) at the upstream part along the Bangshi River of Dhamrai upazila. A total of three irrigation water samples, two from the Site-I eaeh at the vegetative and reproductive stages and one from the Site-TIat the reproductive stage of rice, were collected following standard methods and techniques. Two irrigated soil samples from the Site-I and one sample from the Site-I! were also collected from the plough depth on the same day ofwatcr sample collection following standard guidelines. Water and soil samples were analyzed on spots and in laboratories ofInstitute of Water and Flood Management (IWFM), Bangladesh University of Engineering and Technology (BUET); Soil Resource Development lnstitute (SRDT), Ministry of Agriculture; and Bangladesh Council of Scientific and Industrial Research (BCSIR), Ministry of Science and Information and Communication Technology; Dhaka, by using standard methods and instruments. A number of growth and yield parameters including quality and price of rice from both sites were collected through measurements in the rice fields and surveys at farmers' households. The results of the analysis revealed that the values of pH, EC, DO, Cl, NI-'4-N, SAR and most heavy metals, such as Cu, Fe, Mil, Pb, Cd, Ni and Cr except for Zn and As, exceeded the safe limits for irrigation at the polluted site. However, the parameters were within the safe limits for irrigation at the control site. The soils of both sites were silty clay loam, slightly acidie and nonsaline. The contents of OM were medium in both sites, whereas CEC was high in the polluted site and medium in the control site The contents ofsoi! nutrient ofthe polluted site were found to be higher than those of the control site, except for B The average concentrations of heavy metals in soils were found to be significantly higher at the Site- I than those of the Site-H. Though the nutrient content of soil was higher at the polluted site and the fanning practices were similar at both sites, the growth and yield parameters of rice were adversely affected at the polluted site. The average plant height, root length, panicle length, number of tillers per plant, number of grains per panicle, weight of 1000 grains, unhusked and husked grain yield, and straw yield were about 22, 33, 24, 42, 45, 15, 30 and 42, and 31% lower but the weights of unfilled/damaged grains and rice husks were about 108and 37% higher at the polluted site than those of the control site. These might be due to the combined adverse effect of high salinity and alkaline nature of irrigation water, higher concentrations of heavy metals in both water and soil, and the excessive concentration of~-N in water at the polluted site. The rice grains were of poor quality, i.e. gray in color and small in size in unhuskcd, husked and boiled conditions, and bitter taste in boiled condition at the polluted site. The quality of rice grains ill all conditions was found to be better in color, size and taste at the control site. The poor quality of rice at the polluted site were likely due to the adverse effects of irrigation water containing excessive salts and heavy metals on nutrient uptake and heavy metal accumulation in rice grains. The continuous consumption of heavy metal accumulated rice grains could greatly increase the health risks of the farmers in future. Both the reduction in yield and the poor quality of rice at the polluted site resulted in lower farm income of about 34% and 50''10 per hectare in unhusked and husked conditions, respectively, compared to those at the control site. However, the fanners of the polluted site are not shifting to groundwater irrigation due to the traditional practice, financial viability and social acceptability.