Calvin Trostle

Castor (Ricinus communis L.) Tolerance to Postemergence Herbicides and Weed Control Efficacy

Potential US castor production is limited due to only one labeled herbicide (trifluralin). Field studies were conducted at two Texas locations during 2008 and 2009 to evaluate postemergence herbicides for castor tolerance and weed control efficacy. Clethodim and fluazifop-P-butyl caused no castor stunting while acifluorfen, bentazon, imazethapyr, and lactofen caused stunting which ranged from 5 to 46%. Imazapic and 2,4-DB caused the greatest stunting (44 to 99%) and resulted in castor yields of 0 to 45% of the untreated check. Acifluorfen, imazapic, imazethapyr, lactofen, and 2,4-DB controlled at least 80% smellmelon (Cucumis melo L. var. Dudaim Naud.) while clethodim and fluazifop-P-butyl controlled at least 98% Texas millet [Urochloa texana (Buckl.) R.Webster]. Imazapic and imazethapyr provided 57 to 75% Texas millet control. Results suggest that castor tolerance to the graminicides, clethodim, and fluazifop-P-butyl is high; however, castor injury and yield reductions with the postemergence applications of broadleaf herbicides suggest that these herbicides should not be used in castor production.

Abiotic Factors Affecting Canola Establishment and Insect Pest Dynamics

Canola is grown mainly as an oil-seed crop, but recently the interest in canola has increased due to its potential as a biodiesel crop. The main objectives of this paper were to evaluate effects of abiotic factors and seed treatment on canola plant establishment and pest pressure in the Southern High Plains of Texas. Data was collected at two field locations during the first seven months of two field seasons. Based on multi-regression analysis, we demonstrated that precipitation was positively associated with ranked plant weight, daily minimum relative humidity and maximum temperature were negatively associated with plant weight, and that there may be specific optimal growth conditions regarding cumulative solar radiation and wind speed. The outlined multi-regression approach may be considered appropriate for ecological studies of canola establishment and pest communities elsewhere and therefore enable identification of suitable regions for successful canola production. We also demonstrated that aphids were about 35% more abundant on non-treated seeds than on treated seeds, but the sensitivity to seed treatment was only within four months after plant emergence. On the other hand, seed treatment had negligible effect on presence of thrips.

Soil Ammonium Diffusion Constraints Contribute to Large Differences in Nitrogen Supply to Rice in the Southern United States

This study was to determine if diffusion of soil ammonium may explain why many sandy soils have greater nitrogen (N)–supplying capacity to rice than clay soils. A laboratory procedure using transient-state methods measured the linear movement of soil ammonium (NH4) in tubes packed with five field soils under aerobic conditions. Ammonium diffusion was measured by sectioning tubes after 48 h of equilibration and then measuring NH4 by steam distillation. Effective diffusion coefficients, De, and NH4 diffusion distance, d, per day ranged from De = 4.6 × 10−5 cm2 d−1 and 1.5 cm d−1 for Katy sandy loam to De = 2.9 × 10−7 cm2 d−1 and 0.11 cm d−1 for League clay. Ammonium diffusion distance d was strongly related to soil clay content and hence was predicted by d = Y × {[100/(% clay)] − 1}, where Y is set to 0.1. Predicted d and measured d were highly related (R2 = 0.99).

Linear and Cyclophosphates as Sources of Phosphorus for Corn

Abstract Cyclophosphates are not adsorbed by soil constituents and can be mobile in the soil profile. Mobile phosphorus (P) sources are of interest in soil science and for agronomic practices. Cyclotri (Na3P3O9; C3P), and cyclotetraphosphate (Na4P4O10; C4P) were compared to linear, ortho‐, pyro‐, and tripolyphosphate in four soils with different chemical, physical, and biological properties to determine their mobility and availability to corn (Zea mays, L.) in laboratory and greenhouse experiments. Cyclophosphate (C3P and C4P) hydrolysis products were evaluated by ion chromatography after incubating for 6 to 192 h with 100 and 200 µg P g−1 soil. Phosphorus distribution and mobility, and plant availability and uptake with time, were determined in 45‐cm columns for four soils. Cyclophosphates sorbed less and moved deeper in all soils compared to the linear phosphates. The results showed that after 24 h a large proportion of cyclophosphates (34% of C3P and 37% of C4P) remained unhydrolyzed in Falba sandy acid soil. Split application of C3P and C4P at planting and at booting stage increased corn yield in sandy acid soil. Results of this experiment suggest that P deficiency after plant establishment can be corrected with cyclophosphates in soils with a low potential for cyclo‐P hydrolysis.