Rice Response to Boron Application Rate and Time in Arkansas, Louisiana, and Missouri

Transcription

1 RICE CULTURE Rice Response to Boron Application Rate and Time in Arkansas, Louisiana, and Missouri N.A. Slaton, P.K. Bollich, D. Dunn, J.R. Ross, M. Mozaffari, and L. Espinoza ABSTRACT Boron (B) deficiency of soybean has been routinely observed in numerous fields in northeast Arkansas since 2001 and has stimulated interest in B fertilization of both rice and soybean in Arkansas. In 2002, scientists from Arkansas, Louisiana, and Missouri established similar research trials in each state to investigate rice yield response to B fertilization. Boron fertilizer was applied at rates of 0, 0.33, 0.67, and 1.0 lb B/acre at three or four different times during the season including preemerge, preflood, latetillering or panicle initiation, and the late-boot stage. Boron fertilization increased rice yields only in Arkansas. Although the yield increase was statistically significant it was relatively small (+5.0%). In general, B does not appear to be a major yield-limiting factor for rice production in the Midsouth. Additional research data are needed to determine if the positive yield response observed in Arkansas in 2002 can consistently be repeated before recommendations can be made to growers. INTRODUCTION Boron deficiency of soybean [Glycine max (L.) Merr.] has been routinely observed in numerous fields in northeast Arkansas since Rice (Oryza sativa L) is grown in rotation with soybean in all the mid-south rice-producing states (i.e., Arkansas, Louisiana, Missouri, and Mississippi). While B-deficient rice has never been documented in commercial production fields, recent work performed in Louisiana and Missouri suggests that rice yield responses to B are possible (Dunn and Jones, 2001; Yu and Bell, 1998). The Arkansas counties (i.e., Craighead, Cross, Jackson, and Poinsett) where B-deficient soybean has been observed represent the single largest, multi-county 315

2 AAES Research Series 504 rice producing area in the state and raise questions on the potential benefits of direct B fertilization of rice and concerns about possible toxicity effects that may occur on rice, which has a much lower, although poorly defined, B requirement than soybean. This report describes the results of research trials initiated by scientists at the University of Arkansas (UA), Louisiana State University (LSU), and the University of Missouri during The overall objective of these studies was to evaluate rice grain yield response to B fertilizer application rate and time (growth stage) in field studies. PROCEDURES In 2002, a total of four studies was established to evaluate the effect of B fertilizer rate and application time on rice yield in Arkansas, Louisiana, and Missouri. The soils at the UA Pine Tree Branch Experiment Station (PTBS), LSU Crowley Rice Research Station (2 tests, LSU-1 and LSU-2), and Missouri Rice Research Farm (MRRF) were classified as Calhoun, Crowley, and Crowley silt loams, respectively. Management of rice during the growing season was similar among the studies performed in the all three states. Seedbeds were prepared using conventional tillage. Wells, a long-grain rice cultivar, was drill seeded at ~100 lb/acre 16 April at the PTBS, 21 March at LSU-1, and 5 April at LSU-2. At the MRRF, the long-grain cultivar Cocodrie was seeded on 22 May Composite soil samples were taken from the unfertilized soils and analyzed for soil chemical properties by laboratories in each state (Table 1). In Arkansas, soils were oven-dried, crushed, sieved to pass through a 2-mm sieve, and extracted with Mehlich 3 for plant-available nutrients, including B. Mehlich 3 typically extracts 2 the B extracted by the hot-water method (unpublished data from the NAPT program coordinated by Dr. Robert Miller, Colorado State Univ.). Soils from the LSU sites were extracted with Bray 2 for P, ammonium acetate for cations, and DTPA for micronutrients. Soil samples collected from the MRRF were extracted with Bray 1 for P, ammonium acetate for cations, DPTA for micronutrients, and hot water for plant-available B. At the PTBS, LSU-1, and LSU-2 sites, broadcast applications of P and K fertilizers were applied to the entire plot area before or after seeding to ensure these nutrients were not yield-limiting factors. Studies at the PTBS and MRRF received 120 lb N/acre as urea before flooding. At the LSU sites, a preflood N rate of 165 lb N/acre as urea was applied. Rice management with respect to fertilization, irrigation, and pest control was similar to guidelines recommended by each state s cooperative extension service for the dry-seeded, delayed-flood rice cultural system. Boron was applied at rates of 0.33, 0.67, and 1.0 lb B/acre as Solubor at three or four different times (growth stages) including preemerge or preplant, preflood, latetillering or panicle initiation, and late-boot stage (only at the PTBS) at or just before flag-leaf emergence. All B-rate and application-time combinations were compared to an unfertilized control. Boron was applied with a backpack sprayer calibrated to deliver 10 gal/acre at 3 mph. At each application time, the appropriate amount of Solubor was mixed with water to deliver the specified rates. At maturity, each plot was harvested with a small plot combine for grain yield. Grain moisture was adjusted to a uniform content of 12% for statistical analysis. 316

3 B.R. Wells Rice Research Studies 2002 At all locations, whole-plant samples were taken at panicle initiation and flag-leaf samples were taken at the late-boot stage for elemental analysis. Only dry matter data from the panicle-initiation samples taken at the PTBS will be presented. Whole-plant samples were harvested at the soil level from a 3-ft section of row from the first inside row, dried, weighed, and ground for digestion. Tissue B concentrations among treatments were not significantly different and, therefore, data will not be presented. The treatments at the PTBS were arranged in a 3 (B application rate) 4 (time of application) randomized complete block factorial design and were compared to an untreated control with four replications. At the two LSU sites, the treatments were a randomized complete block design with a 4 (B application rate) 3 (time of application) factorial treatment arrangement with four replications. At the MRRF, the experiment was a randomized complete block design, 3 (B application rate) 3 (time of application) factorial treatment arrangement with four replications. Mean separations were performed by Fisher s protected least significant difference (LSD) at a significance level of 0.05 or RESULTS AND DISCUSSION Arkansas Results At the PTBS, B-application rate (P = ) and the interaction (P = ) between B rate and application time did not affect rice dry matter at panicle differentiation or grain yield (data not shown). However, the time (growth stage) of B application did affect rice dry matter (P = ) and yield (P = ,Table 2). Boron applied preemerge and preflood, averaged across B application rates, produced similar dry matter yields, which were significantly higher than the unfertilized control or B applications made at late tillering < 10 days before sampling. Only B applications made at late tillering, averaged across B rates, produced significantly greater yields than the unfertilized control. Although the yield increase was statistically significant it was relatively small (~5.0%). The data from this single study are not conclusive, yet they suggest that early applications of B failed to affect rice yield, but slightly increased vegetative growth. We initially hypothesized that B would not affect vegetative growth, regardless of application rate or time, and, if beneficial to rice yield, applications near or after panicle initiation (or the beginning of reproductive growth) but before heading would be the most responsive period for B application. Elemental analysis of the sampled rice tissues is not yet completed and will be presented in a future report. Louisiana Results Boron application time, rate, or the B application time rate interaction did not significantly affect grain yield of Wells rice in either study conducted in Louisiana (Table 3). Whole-plant tissue samples taken just prior to the B application at panicle initiation and flag-leaf samples taken at the late-boot stage contained similar B concen- 317

4 AAES Research Series 504 trations among treatments (data not shown). The mean whole-plant B concentrations were 9.4 and 5.6 mg B/kg at the LSU-1 at LSU-2 sites, respectively. At the late boot stage, the mean flag-leaf B concentrations were 8.9 and 6.6 mg B/kg at the LSU-1 at LSU-2 sites, respectively. Missouri Results At the MRRF site, B application time (P = ), rate (P = ), or their interaction (P = ) did not affect rice grain yields (Table 4). Tissue concentration data (not shown) suggested that a K deficiency may have limited rice growth at this site. Tissue samples taken 25 June (only preemerge and control treatments) and 25 July (control, preemerge and preflood treatments) failed to show a significant effect for B application rate, time, or an interaction on tissue-b concentration of whole rice plants. Mean tissue-b concentrations on 25 June (seedling samples taken before flooding) and 25 July (panicle initiation samples) were 14.1 and 5.8 mg B/kg, respectively. SIGNIFICANCE OF FINDINGS The single year of data collected in 2002 from three different mid-south riceproducing states indicated that B was not a major yield-limiting factor for rice grown on silt loam soils. Although rice yields were significantly increased by some B fertilizer treatments at the PTBS, additional data are needed to show that this response is consistent before recommendations can be made to growers. Of the three geographic regions represented by these trials, B deficiency has only been identified near the PTBS and only when soybean is grown. Growers in this northeast Arkansas area should apply B fertilizer directly to soybean as outlined by Slaton et al. (2002) but not directly to rice until more conclusive evidence is collected. ACKNOWLEDGMENTS Funding was provided by the Rice Check-off Funds, Fertilizer Tonnage Fees, U.S. Borax, and the Foundation for Agronomic Research. LITERATURE CITED Dunn, D. and S. Jones Boron fertilization of rice. (Available On-line at agebb.missouri.edu/rice/research/00/pg10.htm) (verified 4 Jan. 2002). Slaton, N.A., L. Ashlock, J. McGee, E. Terhune, R. Wimberly, R. DeLong, and N. Wolf Boron deficiency of soybean in Arkansas. In: N.A. Slaton (ed.). Wayne E. Sabbe Arkansas Soil Fertility Studies University of Arkansas Agricultural Experiment Station Research Series 490: Fayetteville. 318

5 B.R. Wells Rice Research Studies 2002 Yu, X. and P.F. Bell Nutrient deficiency symptoms and boron uptake mechanisms of rice. J. Plant Nutr. 21: Table 1. Selected soil chemical properties (samples taken to a depth of ~4 to 6 inches) for four B fertilization studies conducted at the UA Pine Tree Branch Experiment Station (PTBS) near Pine Tree, AR, the LSU Crowley Rice Research Station near Crowley, LA, and the University of Missouri Rice Research Farm near Malden, MO, during Soil nutrients Location ph P K Ca Mg Fe Mn Zn B (mg/kg) PTBS z LSU-1 y LSU-2 y MRRF x z Values are the mean of 6 composite samples from the 0- to 4-in. soil depth collected from each unfertilized control of each study. Samples from all studies conducted in Arkansas were extracted with Mehlich 3 solution at a soil:solution ratio of 1:10. y Samples from LSU were extracted with ammonium acetate for cations, Bray 2 for P, and DPTA for the listed micronutrients. x Samples from MO were extracted with ammonium acetate for cations, Bray 1 for P, DPTA for micronutrients, and hot-water extraction for B. Table 2. Effect of B application time on rice dry matter production at panicle differentiation (PD) and rice grain yield at maturity at the Pine Tree Branch Station near Pine Tree, AR, during B application time Dry matter at PD Grain yield (lb/acre) (bu/acre) None Preemerge Preflood Late tillering Late boot LSD (0.10)

6 AAES Research Series 504 Table 3. Summary of Wells rice yields by B rate and time of application for two studies conducted at the LSU Crowley Rice Research Station located in Crowley, LA. Note: Data are shown for reference only. No significant differences among grain yields were measured at either test site. Test site B rate B application time LSU-1 LSU-2 (lb B/acre) (lb/acre) Preplant Preplant Preplant Preplant Preflood Preflood Preflood Preflood Panicle initiation Panicle initiation Panicle initiation Panicle initiation Table 4. Cocodrie rice grain yield response to B fertilization rate and time of application compared to an unfertilized control at the Missouri Rice Research Farm located near Malden, MO. Note: Data are shown for reference only. No significant differences among grain yields were measured. B application rate Preplant Preflood Panicle initiation (lb B/acre) (bu/acre)