Timothy W. Walker

FIELD AND LABORATORY STUDIES COMPARING NUTRISPHERE-NITROGEN UREA WITH UREA IN NORTH DAKOTA, ARKANSAS, AND MISSISSIPPI

Nitrification and ammonia volatility are two important impediments to nitrogen (N) use efficiency and crop uptake around the world. Nutrisphere® is a relatively new product whose manufacturer claims both nitrification and urea volatilization inhibiting properties. Urea coated with Nutrisphere is and the resulting fertilizer is called Nutrisphere®-N urea, or Nutrisphere-N (NSN). Eight field studies on spring (Triticum aestivum L.) or durum [T. turgidum L. subsp duram (Desf.) Husn.] wheat in North Dakota, three field studies in Mississippi/Arkansas on rice (Oryza sativa L.), four laboratory experiments in North Dakota and one in Arkansas were conducted to determine the nitrification and urea volatilization inhibiting ability of NSN compared with urea alone. Results of field and laboratory experiments revealed that the product has no nitrification or urea volatilization inhibiting properties at the recommended rates and spring wheat and rice did not benefit from the application of NSN to urea.

Rice Cultivar Response to Penoxsulam

A study was conducted in 2005 and 2006 to evaluate the response of 10 rice cultivars to penoxsulam applied at 70 g ai/ha to two- to three-leaf rice. A related study was conducted in 2004 and 2005 to compare the rice response to applications of penoxsulam at 35 and 70 g/ha and bispyribac-sodium at 28 g ai/ha. In the first study, all 10 rice cultivars exhibited tolerance to penoxsulam as evidenced by plant height, number of days to 50% heading, and rice grain yield. In the second study, applications of both rates of penoxsulam and bispyribac-sodium reduced mass of rice roots 65 to 71% 2 wk after treatment compared with a nontreated control. However, rice grain yield was higher following application of penoxsulam at 70 g/ha compared with yield of the nontreated control or yield following penoxsulam at 35 g/ha and bispyribac-sodium. Rice recovered from injury observed following herbicide application with no negative impact on grain yield. Results indicate that, even though rice root injury can be severe following application, penoxsulam is safe for application to rice cultivars currently grown in the southern U.S. Rice Belt. Nomenclature: Penoxsulam; bispyribac-sodium; rice, Oryza sativa L.

Differential Tolerance of Clearfield Rice Cultivars to Imazamox

Abstract Field studies were conducted to compare the response of one inbred (‘CL161’) and two hybrid (‘CLXL729’ and ‘CLXL745’) Clearfield (CL) rice cultivars to imazamox. Imazamox was applied at 44 and 88 g ai ha−1 to rice in the panicle initiation (PI) and PI plus 14 d (PI + 14) growth stages and at 44 g ha−1 to rice in the midboot growth stage. Maturity of hybrid CL cultivars was delayed following imazamox at 44 g ha−1 applied at PI + 14 and midboot. Furthermore, imazamox at 44 g ha−1, applied at midboot, delayed maturity of CLXL745 more than CLXL729. Expressed as a percentage of the weed-free control plots, rough rice yields for CLXL729 were 91% following imazamox at 44 g ha−1 applied at PI + 14, 78% following imazamox at 44 g ha−1 applied at midboot, and 77% for imazamox at 88 g ha−1 applied at PI + 14. Rough rice yield for CLXL745 was 77 to 92% of the control following all imazamox treatments. All imazamox treatments reduced CLXL745 rough rice yield compared with CL161. Rough rice yield, pooled across CL cultivar, varied with imazamox treatment between years, and these differences may have been a consequence of lower temperatures and solar radiation in the first year. Hybrid CL cultivars CLXL729 and CLXL745 were less tolerant than was CL161 when imazamox was applied at nonlabeled rates (88 g ha−1) and/or timings (PI + 14 or midboot). Because of variability in rice growth stages and irregularities in imazamox application in commercial fields, inbred CL cultivars should be planted where an imazamox application will likely be required. Nomenclature: Imazamox; rice, Oryza sativa L

Control of Volunteer Glyphosate-Resistant Soybean in Rice

Abstract Two field studies were conducted in 2007 and 2008 to evaluate at-planting burndown and POST herbicide applications targeting volunteer glyphosate-resistant (GR) soybean in rice. In the burndown study, paraquat, glufosinate, and a thifensulfuron plus tribenuron mixture were applied immediately after rice seeding. Paraquat controlled volunteer GR soybean at least 95% at all evaluations both years. Control with glufosinate was greater in 2007 than 2008 due to rainfall that occurred following application the second year. The thifensulfuron plus tribenuron mixture provided similar control in both years, but control never exceeded 71%. Additionally, a study was conducted evaluating POST-applied rice herbicides including propanil (4,480 and 2,240 g ai/ha), triclopyr (420 and 210 g ai/ha), bispyribac-sodium (38 and 19 g ai/ha), penoxsulam (40 and 20 g ai/ha), and halosulfuron (70 and 35 g ai/ha). Control across all POST herbicides and application rates was equivalent (> 95%) 28 and 56 d after application except for propanil, which controlled volunteer GR soybean less than other treatments. Volunteer GR soybean can be effectively managed in a rice production system with at-planting burndown or POST herbicide applications in rice. Nomenclature: Bispyribac-sodium; glufosinate; halosulfuron; paraquat; penoxsulam; propanil; thifensulfuron; tribenuron; triclopyr; rice, Oryza sativa L.; soybean, Glycine max (L.) Merr.

Effect of Postflood Quinclorac Applications on Commercial Rice Cultivars

Abstract Rice cultivar, growth stage at application, or both may influence rice tolerance to quinclorac. Field studies were conducted to compare the response of five rice cultivars ‘Bowman’, ‘Cheniere’, ‘CL161’, ‘Cocodrie’, and ‘XL723’ to postflood quinclorac applications. Quinclorac at 0.56 kg ai ha−1 was applied 2 and 4 wk after flood (WAF). Pooled across quinclorac application timings, no differences in maturity were detected among the cultivars in 2008, but maturity of Cheniere and XL723 were delayed compared with CL161 and Cocodrie in 2007. Maturity of Cheniere and XL723 was delayed in 2007 compared with 2008. Pooled over cultivar, maturity was similar for 2 and 4 WAF applications in 2007 but was delayed for 2 WAF treatments in 2008. Regardless of year, postflood quinclorac applications reduced rough rice yield of all cultivars except Bowman. Cheniere and XL723 had lower rough rice yields compared with other cultivars in 2007; however, in 2008, rough rice yields of Cheniere, CL161, Cocodrie, and XL723 were similar, but still lower, than that of Bowman. Pooled over cultivar, postflood quinclorac reduced rough rice yields more when applied 4 WAF than at 2 WAF during both years. Our results demonstrate that Cheniere and XL723 are less tolerant than Bowman is to postflood quinclorac applications and that all evaluated cultivars are more susceptible to quinclorac applied at later developmental stages. Consequently, if circumstances necessitate a postflood quinclorac application, the herbicide should be applied no later than panicle initiation and should not be applied to Cheniere or XL723. Nomenclature: Quinclorac; rice, Oryza sativa L.

Clomazone and Starter Nitrogen Fertilizer Effects on Growth and Yield of Hybrid and Inbred Rice Cultivars

Cultivar and/or application of early-season (starter) nitrogen (N) fertilizer may influence rice tolerance to clomazone. Field studies were conducted to compare the response of hybrid and inbred rice cultivars to applications of clomazone and starter N fertilizer treatments. The inbred cultivar ‘Cocodrie’ and the hybrid cultivar ‘XL723’ were treated with clomazone at 0, 420, or 672 g ai ha-1 immediately after seeding, and starter N fertilizer was applied at 0 or 24 kg N ha-1 when rice reached the two-leaf growth stage. Pooled across clomazone rates and starter N fertilizer treatments, height of Cocodrie 1 week after emergence (WAE) was greater than that of XL723 in 1 of 3 yr. The difference in height between Cocodrie and XL723 resulted from greater clomazone injury 1 WAE on XL723 compared with Cocodrie. No differences in rice height 3 WAE were detected between Cocodrie and XL723 in 2 of 3 yr. when data were pooled across clomazone rates and starter N fertilizer treatments. Injury 3 WAE was similar for Cocodrie across the 3 yr., but injury on XL723 was greater in 1 of 3 yr. Rough rice yield was lower in plots treated with either rate of clomazone where no starter N fertilizer treatment was applied; however, in plots receiving a starter N fertilizer treatment, no effect of clomazone rate on rough rice yield was observed. Clomazone rate did not influence rough rice yield of Cocodrie in any single yr., but rough rice yields of XL723 were lower in plots receiving clomazone compared with plots that received no clomazone in 1 of 3 yr. Therefore, differential susceptibility to clomazone between Cocodrie and XL723 exists based on early-season response and rough rice yield. Starter N fertilizer treatments were beneficial for overcoming yield reductions due to clomazone injury. Nomenclature: Clomazone, rice, Oryza sativa L.

Pendimethalin Applications in Stale Seedbed Rice Production

Abstract Field studies were conducted from 2005 through 2007 to determine the response of three rice cultivars (‘Cocodrie’, ‘Wells’, and ‘Lemont’) to three application timings and two formulations of pendimethalin in a stale seedbed rice production system. Pendimethalin formulated as an emulsifiable concentrate and capsule suspension was applied to rice 0, 3, and 7 d after planting. No visual injury was detected for any cultivar. Seedling density, days to 50% heading, and rice yield were not affected by pendimethalin formulation or application timing. The practice of planting cultivars with excellent seedling vigor into nondisturbed soils with greater available moisture could provide an opportunity to use pendimethalin as a preemergence herbicide for rice production. Nomenclature: Pendimethalin; rice, Oryza sativa L. ‘Cocodrie’, ‘Wells’, ‘Lemont’

Rice straw incorporated just before soil flooding increases acetic acid formation and decreases available nitrogen

Incorporation of rice straw into the soil just before flooding for water-seeded rice can immobilize mineral nitrogen (N) and lead to the production of acetic acid harmful to the rice seedlings, which negatively affects grain yield. This study aimed to evaluate the formation of organic acids and variation in pH and to quantify the mineral N concentration in the soil as a function of different times of incorporation of rice straw or of ashes from burning the straw before flooding. The experiment was carried out in a greenhouse using an Inceptisol (Typic Haplaquept) soil. The treatments were as follows: control (no straw or ash); incorporation of ashes from previous straw burning; rice straw incorporated to drained soil 60 days before flooding; straw incorporated 30 days before flooding; straw incorporated 15 days before flooding and straw incorporated on the day of flooding. Experimental units were plastic buckets with 6.0 kg of soil. The buckets remained flooded throughout the trial period without rice plants. Soil samples were collected every seven days, beginning one day before flooding until the 13th week of flooding for determination of mineral N- ammonium (NH4+) and nitrate (NO3-). Soil solution pH and concentration of organic acids (acetic, propionic and butyric) were determined. All NO3- there was before flooding was lost in approximately two weeks of flooding, in all treatments. There was sigmoidal behavior for NH4+ formation in all treatments, i.e., ammonium ion concentration began to rise shortly after soil flooding, slightly decreased and then went up again. On the 91st day of flooding, the NH4+ concentrations in soil was 56 mg kg-1 in the control treatment, 72 mg kg-1 for the 60-day treatment, 73 mg kg-1 for the 30-day treatment and 53 mg kg-1 for the ash incorporation treatment. These ammonium concentrations correspond to 84, 108, 110 and 80 kg ha-1 of N-NH4+, respectively. When the straw was incorporated on the day of flooding or 15 days before, the concentration of N-NH4+ in the soil was 28 and 54 mg kg-1, equivalent to an accumulation of 42 and 81 kg ha-1 of N-NH4+, respectively. There was formation of acetic acid in which toxic concentrations were reached (7.2 mmol L-1) on the 15th day of flooding only for the treatment with straw incorporated on the day of flooding. The pH of the soil solution of all the treatments increased after flooding and this increase was faster in the treatments with incorporation of straw, followed by the ash treatment and then the control. After 60 days of flooding, however, the pH values were around 6.5 for all treatments, except for the control, which reached a pH of 6.3. Rice straw should be incorporated into the soil at least 30 days before flooding; otherwise, it may immobilize part of the mineral N and produce acetic acid in concentrations toxic to rice seedlings.

Evaluation of Saflufenacil in Drill-Seeded Rice (Oryza sativa)

Abstract Palmer amaranth is the most common and troublesome broadleaf weed species of rice in Mississippi because of the effects of early-season interference and infestations on rice levees, and herbicides for residual or POST control of Palmer amaranth in rice are limited. Three studies were conducted in 2012 and 2013 to evaluate application rates and timings of saflufenacil in rice and to determine the influence of adjuvants when mixed with saflufenacil applied POST. In a PRE study, no injury occurred after saflufenacil PRE, and no control was observed from carfentrazone. Hemp sesbania and Palmer amaranth control increased with increasing saflufenacil rate when applied PRE. Hemp sesbania control with saflufenacil at any rate PRE was ≤ 25% at 35 d after treatment (DAT). Palmer amaranth and ivyleaf morningglory control with saflufenacil at 75 g ai ha−1 PRE was ≥ 94% 35 DAT. In a POST study, rice injury was influenced by application timing and rate of saflufenacil; however, efficacy was not. Rice injury with saflufenacil at 25 g ha−1 and carfentrazone early POST (EPOST) and late POST was similar 7 DAT. Saflufenacil at 50 and 75 g ha−1 EPOST were the most injurious 7 DAT. Control of hemp sesbania and ivyleaf morningglory was similar for all rates of saflufenacil and carfentrazone; however, Palmer amaranth control with saflufenacil at any rate was greater than that of carfentrazone 14 and 28 DAT. In an adjuvant study, rice injury was influenced by adjuvant and saflufenacil rate. Saflufenacil applied alone or in mixture with crop oil concentrate (COC) was least injurious, and saflufenacil at 50 g ha−1 was more injurious than saflufenacil at 25 g ha−1. Saflufenacil applied in combination with any adjuvant provided better control of hemp sesbania and Palmer amaranth than saflufenacil alone. On the basis of this research, saflufenacil should be applied PRE at 50 or 75 g ha−1, depending on weed spectrum, and POST applications should be made at 25 g ha−1 in combination with COC after the two-leaf rice growth stage. Nomenclature: Carfentrazone; saflufenacil; hemp sesbania, Sesbania herbacea (P. Mill.) McVaugh SEBEX; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; rice, Oryza sativa L. Resumen Amaranthus palmeri es la especie de malezas de hoja ancha más común y problemática en arroz en Mississippi debido a sus efectos en la interferencia temprano durante la temporada de crecimiento y sus infestaciones en los diques en los campos de arroz, además hay pocos herbicidas para el control residual y POST de esta maleza en arroz. En 2012 y 2013, se realizaron tres estudios para evaluar la dosis y momentos de aplicación de saflufenacil en arroz y así determinar la influencia de adyuvantes cuando estos se mezclaron con saflufenacil y fueron aplicados POST. En un estudio PRE, no hubo daño después de aplicaciones PRE de saflufenacil, y no se observó control alguno con aplicaciones de carfentrazone. El control de Sesbania herbacea y A. palmeri aumentó con el incremento en las dosis de saflufenacil cuando se aplicó PRE. A cualquier dosis, el control de S. herbacea con saflufenacil PRE fue ≤25% a 35 d después del tratamiento (DAT). El control de A. palmeri e Ipomoea hederacea con saflufenacil a 75 g ai ha−1 PRE fue ≥94% 35 DAT. En un estudio POST, el daño en el arroz fue influenciado por el momento y dosis de aplicación de saflufenacil, sin embargo, la eficacia no lo fue. El daño en el arroz con saflufenacil a 25 g ha−1 y carfentrazone en POST temprana (EPOST) y POST tardía fue similar a 7 DAT. Saflufenacil a 50 y 75 g ha−1 EPOST fueron los tratamientos más dañinos 7 DAT. El control de S. herbacea e I. hederacea fue similar para todas las dosis de saflufenacil y carfentrazone. Sin embargo, el control de A. palmeri con saflufenacil a cualquiera de las dosis fue mayor que el control con carfentrazone 14 y 28 DAT. En un estudio con adyuvantes, el daño al arroz fue influenciado por el adyuvante y la dosis de saflufenacil. Saflufenacil aplicado solo o en mezcla con aceite concentrado de cultivo (COC) causó menos daño, y saflufenacil a 50 g ha−1 causó más daño que saflufenacil a 25 g ha−1. Saflufenacil aplicado en combinación con cualquier adyuvante brindó mejor control de S. herbacea y A. palmeri que saflufenacil solo. Con base en esta investigación, saflufenacil debería ser aplicado PRE a 50 ó 75 g ha−1, dependiendo del espectro de malezas, y las aplicaciones POST deberían hacerse a 25 g ha−1 en combinación con COC y después del estado de crecimiento de dos hojas del arroz.

MODELING RICE GRAIN YIELD RESPONSE TO NITROGEN FERTILIZATION FOR DELAYED-FLOOD PRODUCTION

Nitrogen (N) fertilization decisions are important for farm profit and environmental stewardship. The objective of this research was to evaluate and compare three models (linear-plateau, quadratic-plateau, and quadratic) that can potentially be used to describe rice yield response to N fertilization. Fertilizer N response trials of four newly released rice cultivars from seven sites located in both Mississippi and Louisiana over a two-year period were used. Similar R2 values indicated that each model fit the data equally well. The linear-plateau model had a tendency to produce lower estimates of the economical optimum N rate (EONR) while providing high estimates of yield at the EONR which, in turn, produced higher economic returns compared with other models. All models were equally stable with respect to input and output cost changes. The model used to predict EONR and economic estimates should be considered when evaluating published planning budgets supplied by economists to producers.