T.K. Das

Effect of weed competition on growth, nutrient uptake and yield of wheat as affected by irrigation and fertilizers

The composite effects of two irrigation frequencies (one irrigation at crown root initiation stage and five irrigations at five critical physiological stages of wheat), eight nutrient treatments consisting of N, P and K either applied alone or in combinations at the recommended doses (N:P 2 O 5 :K 2 O at 120:60:40 kg/ha) on population and dry weight of weeds and on the growth, nutrient uptake and yield of wheat were investigated. Observations on the components of the weed population and their biomass made at 60 DAS did not reveal any significant difference between the high and low frequency irrigation. Among the nutrient treatments, the N-treated plots (N, NP, NK and NPK) had a higher population and biomass of grass weeds, whereas sole P and K application or their combination produced the greater growth of broad-leaved weeds. However, the overall weed competition was significantly higher in the P- and K-treated plots than in the N-treated plots. The NP, NPK, NK and N treatments produced significantly higher values for dry weight, crop growth rate, leaf area, number of tillers, nutrient uptake, number of ear-bearing tillers, protein content and grain yield than the other treatments. Weeds in unweeded control plots did not significantly affect wheat growth (CGR, dry weight, tillers/plant) and uptake of the nutrients except of the P at 60 DAS. However, the number of ear-bearing tillers, grains per ear and yield were significantly higher in the weed-free plots than in the unweeded control treatment.

Persistence of herbicide fenoxaprop ethyl and its acid metabolite in soil and wheat crop under Indian tropical conditions

The persistence of fenoxaprop ethyl {Ethyl (RS)-2-[4-(6-chloro-1,3-benzoxazol-2-yloxy) phenoxy] propionate} herbicide and its active metabolite fenoxaprop acid was investigated in soil and wheat crop. Fenoxaprop acid was prepared by alkaline hydrolysis of fenoxaprop ethyl. A HPLC method was developed in which fenoxaprop ethyl herbicide and its acid metabolite showed sharp single peak at 6.44 and 2.61 min respectively. The sensitivity of the method for ester and acid was 2 and 1 ng respectively with limit of detection of 0.1 and 0.05 μg mL−1. The recovery of fenoxaprop ethyl and fenoxaprop acid from soil, wheat straw and grain ranged between 73.8–80.2%. In a field experiment fenoxaprop ethyl (Puma super® 10 EC) when applied to wheat crop at the rate of 120 g and 240 g a.i. ha-1 as post emergence spray, fenoxaprop ethyl converted to fenoxaprop acid. Residues of fenoxaprop ethyl and acid dissipated in soil with a half-life of 0.5 and 7.3 days, respectively. At harvest no detectable residues of fenoxaprop ethyl or acid were observed in soil, wheat grain and straw samples.

The effects of combining modified sowing methods with herbicide mixtures on weed interference in wheat crops

In India, wheat is prone to being heavily infested with weeds, which cause considerable yield losses. Agronomic practices, including sowing method, influence weed interference in wheat growth. A herbicide mixture is usually more effective than a single herbicide for controlling a broad-spectrum of weeds. It may prevent weed species shift and delay resistance development in weeds. This study attempted to develop an integrated approach, combining a modified sowing method with applying a herbicide mixture for efficient weed management in wheat. We found that flat bed missing-row sowing resulted in significant reductions in: (i) the three-year mean population densities of grassy, broad-leaved and total weeds at 40 days after sowing (d.a.s), (ii) total weed population density and biomass (dry weight) at 60 d.a.s., compared to a mainly, furrow-irrigated raised bed system. Applying a tank-mix of fenoxaprop-p-ethyl at 0.08 kg/ha and isoproturon at 0.4 kg/ha applied 30 d.a.s. resulted in significant reductions in total weed population density and biomass, leading to a significant improvement in wheat growth and yield compared to either a weedy check or a regime of fenoxaprop-p-ethyl applied at 0.10 kg/ha. However, a combination of the flat bed missing-row sowing and tank-mix application of fenoxaprop-p-ethyl 0.08 kg/ha and isoproturon 0.4 kg/ha 30 d.a.s. resulted in higher wheat yield through better management of weeds compared with other sowing/ weed control combinations.

Effects of conservation agriculture on crop productivity and water-use efficiency under an irrigated pigeonpea–wheat cropping system in the western Indo-Gangetic Plains

In search of a suitable resource conservation technology under pigeonpea ( Cajanus cajan L.)–wheat ( Triticum aestivum L.) system in the Indo-Gangetic Plains, the effects of conservation agriculture (CA) on crop productivity and water-use efficiency (WUE) were evaluated during a 3-year study. The treatments were: conventional tillage (CT), zero tillage (ZT) with planting on permanent narrow beds (PNB), PNB with residue (PNB + R), ZT with planting on permanent broad beds (PBB) and PBB + R. The PBB + R plots had higher pigeonpea grain yield than the CT plots in all 3 years. However, wheat grain yields under all plots were similar in all years except for PBB + R plots in the second year, which had higher wheat yield than CT plots. The contrast analysis showed that pigeonpea grain yield of CA plots was significantly higher than CT plots in the first year. However, both pigeonpea and wheat grain yields during the last 2 years under CA and CT plots were similar. The PBB + R plots had higher system WUE than the CT plots in the second and third years. Plots under CA had significantly higher WUE and significantly lower water use than CT plots in these years. The PBB + R plots had higher WUE than PNB + R and PNB plots. Also, the PBB plots had higher WUE than PNB in the second and third years, despite similar water use. The interactions of bed width and residue management for all parameters in the second and third years were not significant. Those positive impacts under PBB + R plots over CT plots were perceived to be due to no tillage and significantly higher amount of estimated residue retention. Thus, both PBB and PBB + R technologies would be very useful under a pigeonpea–wheat cropping system in this region.

Greenhouse gases emission, soil organic carbon and wheat yield as affected by tillage systems and nitrogen management practices

ABSTRACT Agricultural activities are responsible for greenhouse gases (GHGs) emission in the environment. Strategies are required to enhance the soil organic carbon (SOC) and nitrogen (N) sequestration to adapt and mitigate the climate change. We investigated GHGs emission, SOC and N enhancement under conventional tillage (CT) and zero tillage (ZT) with N management in wheat (Triticum aestivum L.). Seasonal carbon dioxide (CO2) emission and global warming potential (GWP) reduced for ZT treatments over CT without residues and 100% of required N with a blanket split application (CT – R + 100N). The ZT with 5 t ha−1 maize (Zea mays L.) residues retention and 75% of required N and GreenSeekerTM (GS)-aided N management (ZT + R + 75N + GS) reduced yield-scaled GHGs emission and increased total organic carbon (C) stock over CT – R + 100N. However, nitrous oxide (N2O) emission was lower in CT. The GS-based N management saved 26–35 kg N ha−1 in different tillage systems in both years over blanket application with higher N uptake and associated reduction in N2O emission. The study recommends that ZT with residues retention and GS-based N management can minimize the GHGs emission and improve the SOC.

Effect of fly ash on persistence, mobility and bio-efficacy of metribuzin and metsulfuron-methyl in crop fields.

Field evaluation of two fly ashes (40t/ha) on persistence, mobility and bioactivity of metribuzin and metsulfuron-methyl was studied in soybean and wheat crops, respectively. Metribuzin was applied as pre-emergence at 0.5kg/ha, while metsulfuron-methyl was applied post-emergence at 8g/ha. Results suggested that metribuzin in surface (0-15cm) soil of fly ash unamended plots reached below detectable limit in 60 days, while herbicide persisted till 112 days in surface soil of fly ash amended plots. No metribuzin leached down to subsurface (15-30cm) soil in fly ash amended plots, while traces of metribuzin (0.6-1.2μg/kg) were recovered in subsurface soil of fly ash unamended plot. Metsulfuron-methyl in surface soil persisted till 15 days in control and 20 days in fly ash amended plots and no metsulfuron-methyl leached down to subsurface soil. Fly ash amendment had no adverse effect on the bioactivity of herbicides and yield of soybean and wheat. The study suggested that fly ash amendment to soil can be exploited to retain applied herbicides in surface soil.

Release behavior and bioefficacy of imazethapyr formulations based on biopolymeric hydrogels

ABSTRACT Controlled release formulations of imazethapyr herbicide have been developed employing guar gum-g-cl-polyacrylate/bentonite clay hydrogel composite (GG-HG) and guar gum-g-cl-PNIPAm nano hydrogel (GG-NHG) as carriers, to assess the suitability of biopolymeric hydrogels as controlled herbicide release devices. The kinetics of imazethapyr release from the developed formulations was studied in water and it revealed that the developed formulations of imazethapyr behaved as slow release formulations as compared to commercial formulation. The calculated diffusion exponent (n) values showed that Fickian diffusion was the predominant mechanism of imazethapyr release from the developed formulations. Time for release of half of the loaded imazethapyr (t1/2) ranged between 0.06 and 4.8 days in case of GG-NHG and 4.4 and 12.6 days for the GG-HG formulations. Weed control index (WCI) of GG-HG and GG-NHG formulations was similar to that of the commercial formulation and the herbicidal effect was observed for relatively longer period. Guar gum-based biopolymeric hydrogels in both macro and nano particle size range can serve as potential carriers in developing slow release herbicide formulations.

Effect of sequential application of metribuzin on selectivity and weed control in soybean

Post-emergence treatments are often the keys to efficient weed control, and could be a substitute or supplementary to pre-emergence treatment. Accordingly, this study was designed to test the selectivity and efficacy of sequential (pre- + post-emergence) applications of metribuzin on weeds in soybean, and to optimize the dose, volume rate and time of application. We observed that sequential metribuzin treatments were more toxic to soil micro-organisms and caused greater inhibition in photosynthesis, acetylene reduction activity and nodulation of soybean compared to only pre-emergence applications of metribuzin or pendimethalin. The negative effects, however, were mitigated by increased activities of superoxide dismutase and ascorbate peroxidase in soybean. The sequential applications left negligible residues at harvest. A sequential application of metribuzin 0.25 kg ha−1 2 days after sowing and 0.1 kg ha−1 20 days after sowing with 200 Lha−1 of water gave a higher seed yield. This ensured the possibility of sequential application of metribuzin with an optimized dose, volume rate and time of application.

Herbicide ready-mixes effects on weed control efficacy, non-target and residual toxicities, productivity and profitability in sugarcane–green gram cropping system

ABSTRACT Weeds pose a major challenge at the initial stages of sugarcane and when uncontrolled cause high yield losses. This study was undertaken to define a better and cost-effective weed management strategy. We compared ametryn + trifloxysulfuron-sodium (hereafter referred to as trifloxysulfuron) ready-mixes with single applications of trifloxysulfuron, atrazine and 2,4-D for efficacy, non-target and residual toxicities, yield and profitability in a sugarcane–green gram rotation. Results showed that a density of 100 weeds m−2 could reduce sugarcane yield by 18.4 t ha−1. The ready-mix ametryn + trifloxysulfuron (1097.3 + 27.8) g a.i. ha−1 applied 15 days after planting (DAP) caused reductions in weed density by 88.2%, 90.9%, and 90.3%, and weed biomass by 68.0%, 53.8%, and 56.2% compared to unweeded control at 30, 60, and 90 DAP, respectively. Consequently, the sugarcane yield, system productivity, and net returns were increased by 92.1%, 43.5%, and 1515%, respectively due to this ready-mix. It increased system productivity by 23%, 17.2%, and 22.7% compared to trifloxysulfuron, atrazine, and 2,4-D treatments, respectively. This ready-mix may be recommended in sugarcane. This would reduce weed seed bank and herbicide application cost by 50%, and prevent/delay weed shift and resistance.

Tillage and nitrogen management effects with sequential and ready-mix herbicides on weed diversity and wheat productivity

ABSTRACT In this experiment, weed management was studied in zero tillage (ZT) and conventional tillage (CT) wheat with and without crop residue and nitrogen (N). The treatment ZT with crop residue retention (R) and 75% of required N plus GreenSeeker™ (GS)-aided N management (ZTRNGS) resulted in a reduction of density and dry weight of weeds compared to CT and ZT without residue. Sequential application of pendimethalin and sulfosulfuron (PMT-SSF) reduced the weed density and dry weight compared to the weedy check (WC). Importantly, the richness and diversity indices were high in ZTRNGS and in WC treatments. Greater wheat grain (5.11 t/ha) and biomass yield (13.31 t/ha) were observed in ZTRNGS than CT without residue and blanket split application of N (CTN). The treatment ZTRNGS recorded 14.1% and 16.9% higher gross and net returns, respectively, over CTN. This study demonstrates that surface retention of crop residue in ZT is more useful than residue incorporation under CT for effective weed control, improving crop yield and profitability.