Evaluation of dicamba volatilization when mixed with glyphosate using imazethapyr as a tracer.

Expansion of dicamba-resistant crops increased the frequency of off-target movement issues, especially in the midsouthern United States. Six field trials were conducted over two growing seasons with the purpose to determine the contribution of volatilization and physical suspension of particles to the off-target movement of dicamba when applied with glyphosate and imazethapyr - a non-volatile herbicide used as a tracer for physical off-target movement. Applications included dicamba at 560 g ha-1, glyphosate at 1260 g ha-1, and imazethapyr at 105 g ha-1. Applicators include glyphosate with dicamba to increase the spectrum of weed control from these applications; however, this addition increases potential for dicamba volatilization. Following application of the mixture, air samplers were placed in the field to collect dicamba and imazethapyr. Results showed there was at least 50 times more dicamba than imazethapyr detected even though the dicamba:imazethapyr ratio applied was 5.3:1. Dicamba was detected in the treated area and the off-site locations and all intervals of air sampling, ranging from 126 to 5990 ng. No more than 37.5 ng of imazethapyr was detected during the first 24-h after application (HAA) inside the treated area. Imazethapyr was only detected in 9 of the 20 sampling combinations during these experiments, and most of these detections (6) occurred during the first 24 HAA and inside the treated area. While some movement from the suspension of particles occurred based on the detection of imazethapyr in air samples, results show that most dicamba detection was due to the volatilization of the herbicide.

Methane emissions from drill-seeded, delayed-flood rice production on a silt-loam soil in arkansas.

Rice ( L.) production is unique among staple food crops because the majority of the growing season typically occurs under flooded-soil conditions. Flooding the soil leads to anaerobic conditions, which are a precursor to methane (CH) production. However, no known research has investigated CH emissions from the drill-seeded, delayed-flood rice production system common in Arkansas, the leading rice-producing state in the United States. Therefore, research was conducted in 2011 to determine the effects of vegetation (rice and bare soil), chamber location (in- and between-rice rows), and nitrogen (N) fertilization (optimal and no N) on CH emissions from a silt-loam soil. Methane fluxes measured weekly from flooding until flood release were affected by vegetation, chamber location, and sample date ( < 0.05). In-row CH fluxes were <0.7 mg CH-C m h until 20 d after flooding (DAF) and <1.0 mg CH-C m h from between-row and bare soil until 41 DAF and were unaffected by fertilization over time. The largest weekly measured CH flux (31.9 mg CH-C m h) was observed from in-row rice at 41 DAF. Post-flood-release CH fluxes were affected by vegetation, fertilization, chamber placement, and sample date ( < 0.05) and accounted for approximately 3 to 7% of the season-long CH emissions. Methane emissions averaged 195 kg CH-C ha per growing season and were unaffected by fertilization. Direct measurement of CH emissions from drill-seeded, delayed-flood rice grown on a silt-loam soil will improve the accuracy of assessments of the carbon footprint and long-term sustainability of rice.

Evaluation of secondary sexual dimorphism of the dioecious Amaranthus palmeri under abiotic stress.

The evolution of secondary sex-specific traits of dioecious species under abiotic stress conditions has received limited research, especially in the case of Amaranthus palmeri, a fast adapting and highly competing plant. Here, we have examined the interactive effects of abiotic stress on mineral accumulation, chlorophyll a and b content, and the operating capacity of Photosystem II (PSII) in both male and female A. palmeri plants grown under three different intensities of white light, and under N, K or P deficiency. Mineral profiling of the leaves and stems (with inflorescence) highlighted intra- and intersexual differences in their accumulation pattern and mineral associations. Chlorophyll a and chlorophyll b were different between the male and the female plants, being slightly lower in the latter, at high light intensity towards maturity, or under K or P deficiency. Further, slight, although statistically significant differences were recorded in the chlorophyll a/b ratio, which was lower at the higher light intensity in the female, over that in the male, plants towards maturity. Chlorophyll fluorescence parameters, i.e., steady state and maximum fluorescence increased under high light intensity, whereas the PSII operating efficiency decreased in the female plants, indicating reduced PSII capacity. Sex-specific differences in A. palmeri showed a differential response to stressful conditions because of differences in their ontogeny and physiology, and possibly due to the cost of reproduction. We suggest that the breeding system of dioecious species has weaknesses that can be used for the ecological management of dioecious weeds without relying on the use of herbicides.