Residues of imazethapyr in soybean grain, straw and soil under application of long term fertilizers in Typic Haplustert

Experiment was conducted to see the effect of balance and imbalance level of nutrients on residue of imazethapyr. Imazethapyr was applied at 100 g/ha 25 days after sowing of soybean crop for managing annual and perennial broad-leaf weeds and sedges. Soil and crop samples were collected at harvest and analyzed by HPLC using photo diode array detector. Retention time of imazethapyr was found to be approximately 3.5 minutes. Residues of imazethapyr in soil at various treatments were found 0.0124 to 0.0121 μg/g. Concentration of imazethapyr in soil was maximum in 100% N + imazethapyr (T ) and minimum in (100% NPK + imazethapyr (T ) treatments respectively. At 7 8 harvest residue of imazethapyr was not found in soybean grains and straw in any set of treatments except T (100% N). 7 Key word: Soil, Soybean grain, Straw, Residue, Imazethapyr, HPLC analysis Imazethapyr belongs to imidazole group with a toxicity class of III and used as a selective herbicide. It is applied as pre-plant incorporated, pre-emergence, and post-emergence to control grasses and broadleaved weeds in pulse crops (Herbicide handbook 1989, Thomson 1993 and Anon. 2006). Chemically, imazethapyr is a weak acid (like amphoteric) having both carboxylic acid and pyridine functional groups thus dissociation to the anion resulting very low sorption at high pH levels. Imazethapyr absorption varies with a number of soil properties but the soil organic carbon content has been considered the single best predictor of sorption for non-polar, non-ionizable organic chemicals. Microbial degradation and photodecomposition have been suggested as major dissipation mechanism for imazethapyr. Imazethapyr incorporated in the soil persisted longer than imazethapyr applied to the soil surface. Vertisols are dark-coloured Montmorillonitic, Hyperthermic and Typic haplustert clay that develop cracks when expending and contracting with changes in moisture content. A few reports showed imazethapyr residues in soil in India (Sondhia 2008) and stream and river water in Midwestern US at concentrations above the maximum residue limits in 71% of samples (Battaglin et al. 2000). Hollaway et al. 2004 reported that 10% residues of applied imazethapyr persisted for 24 and 5 months after treatment in clay soil and sandy soil respectively. Soil pH affects imazethapyr sorption-desorption, which in turn can affect persistence and bioavailability (Bresnahan et al. 2000). Different nutrient level may also affect persistence of herbicides in crop and soil. But hitherto no work has been reported on the behaviors of herbicide persistence under balanced and imbalanced level of nutrients under field conditions in soybean crop. Thus experiment was conducted to examine the residue of imazethapyr in Typic haplustert under application balance and imbalance level of nutrients. A field experiment was conducted on Vertisol in kharif 2007-08 at research farm of Jawahar Lal Nehru Krishi Vishva Vidyalaya, Jabalpur. The soil of the experimental field was medium black belonging to Kheri series of fine montmorillonitic hyperthermic family of Typic Haplustert. The soil was clay loam in texture. The experiment consists of 10 treatments replicated four times in a randomized block design. The gross plot size being 17 x 10.8 m with 1 m spacing in between the plots and 2 m spacing between the replications. The crop was raised under irrigated conditions with recommended package of practices. The recommended fertilizer dose (100% NPK) for soybean crop was applied on soil at the rate, of 20:80:20 NPK respectively through Urea, SSP, DAP, and MOP. Treatments include T (50% NPK), T (100% NPK), 1 2 T (150%NPK), T (100% NPK+Hand Weeding), T 3 4 5 (100% NPK+Zn), T (100% NP), T (100%N), T (100% 6 7 8 NPK+FYM), T (100% NPK – S), T (Control) and 9 10 Short communication