Soil properties and yield of groundnut associated with herbicides, plant geometry, and plastic mulch

Experiments were conducted over 2 years during the dry season of 2002 (June-September) and wet season of 2002-2003 (December-March) at Regional Research Station, Tamil Nadu Agricultural University, Vridhachalam, India, to study the influence of two colors of polyethylene film mulch (black and white polyethylene film mulch), herbicides (Fluchloralin at 1.0 kg/ha and no herbicide application), and three plant geometries [30 x 10 cm, 20 x 20 cm (two seeds/hill), and 20 x 15 cm] on soil properties, growth, and yield of groundnut. Results indicated that the soil physical properties such as rate of water loss/day was highest with white polyethylene film mulch, the hydraulic conductivity of the soil was significantly more with black polyethylene film mulch, and soil bulk density and percentage of pore space did not differ between the two colors of polyethylene films. The rate of water loss was highest with plots with no herbicide, whereas the hydraulic conductivity of the soil was more with herbicide-applied treatments. However, the bulk density and pore space did not differ significantly. The plant geometry did not have any significant influence on any of the soil physical properties. With regard to soil microorganisms, the bacterial and fungal population was significantly higher in black polyethylene film mulch at all the three stages of observation, whereas no significant difference between the colors of polyethylene film mulch was observed for actinomycetes at all the stages of observations. Interestingly, no variation in the population of soil microflora was observed between the herbicide and no-herbicide treatments. The soil-available nitrogen, phosphorus, and potassium (NPK), at harvest, was significantly higher with white polyethylene film mulch, whereas crop NPK uptake was higher with black polyethylene film mulch. The soil-available NPK and crop uptake was higher with herbicide application. The evolution of carbon dioxide (CO2; soil respiration) was significantly influenced by polyethylene film mulch and herbicides, and the evolution of CO2 was altered by the plant geometry. The crop dry-matter production, pegging percentage, pod setting ratio number of matured pods/plant, and pod yield were significantly higher under black polyethylene mulch. Herbicide application significantly improved the majority of the growth and yield attributes and significantly higher pod yield was obtained with herbicide application. However, most of the yield and growth attributes and pod yield were not significantly influenced by the different plant geometries studied.