Management of greater club rush (Scirpus grossus L.f) in wetland rice ecosystem

Abstract

An investigation entitled“ Management of greater club rush (Scirpus grossus L.f) in wetland rice ecosystem’’was undertaken in a wetland rice ecosystem heavily infested with the weed. The study was taken up during February 2010 to January 2011. The main objectives of the experiment were to develop a management strategy for recovering the wetland rice ecosystem invaded by greater club rush, economical analysis of rice cultivation in the land recovered from the invaded weed and study of the weed biology. Laboratory studies conducted at College of Agriculture, Vellayani, were also included to achieve the objectives envisaged. The field experiment on weed management (part I) was laid out in Randomised Block Design with nine treatments and three replications. The treatments included farmer’s practice of tillage, application of lime at two different doses after tillage and application of glyphosate and 2, 4 – D alone and in combination on weed re-growth with and without tillage. Before applying the treatments, the thick growing weed was given an initial mowing. The laboratory studies were done to analyse the herbicide residue in the treated plots and to study the effect of the applied herbicides on the soil microbial population. The treatment adjudged as the most efficient was verified further in a larger plot, by comparing it with the farmer’s practice of weed management to study the economics of rice cultivation in the land recovered from the invasive weed (part II). The biology of greater club rush was also studied simultaneously (part III). The results of the weed management study indicated that all the herbicidal treatments were significantly superior to farmer’s practice of tillage in reducing the weed dry weight. Weed control efficiency was found to be 100 percent throughout the study, when the thick infestation was mowed once and treated with a combination of (glyphosate @1kg ai ha-1 + 2,4-D @ 2 kg ai ha-1) Tillage + glyphosate @1kg ai ha-1 + 2,4-D @ 2 kg ai ha-1 was also effective in controlling the weed, but fragments of root system was found remaining in the soil even after nine months; as a possible source of reinfestation. However, application of lime as a means of controlling greater club rush was found to have no effect on the weed growth. Considering all factors, T7 (glyphosate @1kg ai ha-1 + 2,4-D @ 2 kg ai ha-1) was adjudged as the best treatment for testing further in the farmer’s field (part II ). There was substantial increase in the floristic diversity after the experiment in herbicide treated fields which were completely cleared of greater club rush within 45 days of herbicide application. The residue analysis of the soil collected on the next day of herbicide application revealed that the residue was below detectable limit in the case of both 2, 4 – D and glyphosate, alone as well as in combination. The results on soil microbial population indicated that the soil treated with any of the herbicides had a much higher microbial population than the untreated plots. The cost worked out for the management of the thick infestation of greater club rush was prohibitively high in all the treatments. Economic analysis of rice cultivation in the land recovered from the invasive weed indicated that the grain and straw yield in the treated plot was substantially higher than that from the non treated plots. When the economics was worked out inclusive of the cost of land recovery through eradication of greater club rush, the net profit from rice cultivation was not very high. But the important indication was that the farmers suffered great loss when they followed the present practice of mowing followed by tillage. The observations on the weed biology indicated that in greater club rush, propagation was exclusively through vegetative means. The nutrient composition of the weed was comparable to that of rice plant. Due to its very high biomass production, the nutrient uptake of greater club rush was much higher than that of rice crop.