MSc

The research programme entitled “Influence of weed management practices on the soil quality attributed of Ultisol” consisted of a field experiment and laboratory analysis of soil samples taken from the field experiment. The study was carried out with the objective to evaluate the changes in physical, chemical and biological characteristics of soil in an Ultisol due to different weed management practices in brinjal (Solanum nekibgena L.). The field experiment was conducted at Agronomy Farm attached to the Department Of Agronomy, College of Horticulture, Vellanikkara during June to October 2015. The analysis of chemical and physical characteristics of soil samples was carried out at the Department of soil science and agricultural chemistry and microbiological analysis was performed at the department of plant pathology.

The field was laid out in randomized block design with seven treatments and four replications. The treatments included six weed management practices namely(1) hand weeding, (2) spade weeding,(3) chemical weed control (pendimethalin @1.5 kg ha-1), (4) organic mulching (Glyricidia green leaves), (5) polythene mulching (silver to black bottom polythene, 30 micron), and (6) mulching with coir fibre mat and one unweeded control. The salient results of the experiment are summarized below.

Plots mulched with polythene sheet maintained higher soil temperature (1.2 to 2.70 C higher than the other treatments) throughout the crop period. Among the organic mulches, coir fibre mat increased the soil temperature to a greater extent than green leaves. The other physical properties of soil viz., bulk density, soil moisture content, porosity and water holding capacity were improved by organic mulching. Hand weeding registered significantly lower values especially for soil moisture and water holding capacity of the soil.

Soil PH was significantly lower under polythene mulching than that of hand weeding, un weeded control and pendimethalin treatments. Electrical conductivity was affected by all the treatments with a slight variation. Organic mulching treatments significantly improved the organic carbon and available nitrogen content of the soil, while polythene mulching showed the reverse trend. Available phosphorous content was significantly lower in organic and polythene mulching treatments.

No significant differences were noticed in the content of secondary nutrients in soil except sulphur. The polythene mulched plots increased the available sulphur content of the soil at 90 DAP and lower values were recorded in treatments with hand weeding, pendimethalin and un weeded control.

In the case of macronutrients, no significant differences were on served between the treatments throughout the crop period.

Soil microflora showed an increase in their population in all the treatments except pendimethalin during the period from planting to 30 DAP and then decreased towards the end of study period (90 DAP). Population of bacteria and fungi and dehydrogenase enzyme activity were more facilitated by organic mulching. Significantly lower enzyme activity and microbial counts were recorded in pendimethalin plots throughout the period of experimentation. Mulching with polythene sheet and coir fibre mat also resulted in lower microbial counts.

Weeds were not observed in the polythene mulched plots throughout the crop period. Mulching with coir fibre mat and green leaves were the next best treatments to control germination and further growth of weed. All the plots with mulching treatments recorded lower weed count and weed dry weight compared to the plots without mulching.

The study revealed the superiority of organic mulching with glyricidia leaves in improving the soil quality of Ultisol. Polythene mulching gave 100% weed control with two fold increases in yield compared to organic mulching with glyricidia leaves. However, it showed deleterious effects particularly on biological properties of soil viz; population of bacteria and fungi and dehydrogenase activity. The inefficacy of herbicide pendimethalin was comparatively low due to the profuse growth of weed flora after the commencement of south west monsoon. The adverse effects of this chemical on soil micro flora and dehydrogenate enzyme activity as evidenced from the present study neccessiates a reduction in the use of pendimethalin for weed control in vegetables.