Tillage Effects on Stand and Yield in a Rice Monoculture System

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J. A. Wrather, W. E. Stevens, D. J. Dunn, University of Missouri-Delta Center, P. O. Box 160, Portageville 63873; R. D. Cartwright, University of Arkansas, P. O. Box 391, Little Rock 72203; G. L. Sciumbato, Mississippi State University, P. O. Box 197, Stoneville 38776; and D. H. Beighley, Southeast Missouri State University, 700 North Douglas, Malden 63863

Abstract

Our objective was to determine if tillage (disk fall and spring, disk fall only, or no tillage) affected rice diseases, plant population density, and yields in a rice monoculture system. Stem rot was the only disease that developed in plots during 1994, and the severity index was the same for all tillage treatments. Diseases did not develop in plots during 1995 and 1996. Tillage treatments did not affect rice plant population or yields. This is the first report on the effects of tillage on stand and yield in a rice monoculture system. A fall-only tillage system (stale seedbed) may be useful to some rice producers in the central USA because yields are similar to those in a conventional tillage system. Ruts in the field due to harvest equipment could be eliminated by fall tillage, and tillage in the spring would not be necessary prior to planting and application of a burn-down herbicide.

Introduction

Producers in the USA planted 25.5% of rice (Oryza sativa L.) in a reduced and/or conservation tillage system in 2000 compared to almost 0% in 1980 (5). The adoption of conservation tillage by rice producers has been in part to reduce labor and production costs. Much information is available on the effects of reduced tillage systems on soybean (Glycine max L.) diseases and yields (6,7,10,11,12), but information about the effects on rice diseases and yields in the USA is very limited. Wilson et al. (9) conducted experiments in an Arkansas rice field with a history of salinity injury, and it was in rotation with soybean. They determined that the level of salinity in the rice root zone prior to permanent flood establishment was significantly greater for no tillage than conventional tillage treatments, and yields averaged over years were lower for no-tillage than conventional tillage treatments. Cartwright et al. (1) determined that rice yield was significantly lower for no-till compared with conventional tillage treatments in a rice-soybean rotation system. Lower yields were attributed to significantly lower seedling population density for the no-till compared with conventional tillage treatments. Yields were similar for the fall-only tillage (stale seedbed), and fall and spring tillage treatments. Information about the effects of tillage on rice diseases, plant population density, and yield in fields monocultured to rice has not been published. The objective of this project was to determine if tillage affected rice diseases, plant population density, and yields in a rice monoculture system.

Fig. 1. Rice seedlings in no tillage (left) and disk-tillage fall and spring (right) areas.

Field Experiments Using Several Tillage Treatments

In October 1992, a tillage experiment was established in a field at the Missouri Rice Research Farm located near Qulin, Missouri (36.6°N, 90.1°W) that had previously been planted to soybean in 1992. The soil was a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf) consisting of 35% sand, 29% silt, and 36% clay. Tillage treatments were disk-tillage fall and spring, disk-tillage fall only, or no-tillage (soil left undisturbed). Disking was done to a 4-inch depth. Rice stems left after harvest in no tillage plots were cut with a 6-ft wide rotary mower leaving 6-inch of stem above ground. Treatments were maintained in the same plots each year. Each plot was 10-ft wide and 30-ft long. The experimental design was a randomized complete block with 4 replications. The field was seeded to rice in 1993-1996. Data were only collected during 1994-1996.

Vegetation in all plots was chemically killed with paraquat (0.816 lb/acre) 10 days prior to seeding rice. Rice, ‘Lemont,’ was planted 10 May 1994, 15 May 1995, and 12 May 1996 at 90 lb/acre on 7.5-inch row spacing. All plots were treated with propanil (3.7 lb/acre) 14 days after rice seedling emergence and again at the V5 stage of growth (2). Plots were almost completely weed-free. Nitrogen, 180 lb/acre, was applied at V5 stage of growth followed immediately by establishment of a permanent flood. The flood was maintained at 2- to 3-inch deep until R7 stage of growth.

Fourteen days after rice emergence, the population density was determined by counting all plants in five 3-ft-long sections of row arbitrarily selected from the center area of each plot. Disease incidence and severity at R1, R2, R4, and R7 stages of growth were determined for five arbitrarily selected 3-ft-long sections of row from the center area of each plot. Each year, the central 6-ft-by-30-ft area of each rice plot was harvested, and yields were adjusted to 13% moisture. Surface water drained quickly from this site, and the soil dried quickly. Harvest equipment left no ruts in the field during 1992-1996 because the soil was dry at harvest. This facilitated post harvest tillage and mowing of rice stems in no-tillage plots.

Statistical analysis for tillage effects on rice stand, disease incidence and severity, and yield were performed using SAS mixed model procedures (SAS Institute, Cary, NC). The Mixed Model procedure provides Type III F values, but it does not provide mean square values for each element within the analysis or the error terms. Mean separation was evaluated through a series of protected pair-wise contrasts among all treatments (3). Probability levels greater than 0.05 were categorized as not significant.

Tillage Effects on Rice Diseases, Plant Density, and Yield

The analysis of variance indicated tillage × year interactions were not significant for stands and yields. Tillage treatments did not affect rice stands or yields among years (Table 1). Yields averaged over tillage treatments were significantly greater for 1995 (5382 lb/acre) and 1996 (5616 lb/acre) compared to 1994 (3582 lb/acre). Yields for 1995 and 1996 were similar to average Missouri yields those years. The low yields during 1994 were attributed to yield suppression due to stem rot.

Table 1. Tillage effects on rice stand (living plants per 3-ft row) and
yield (lb/acre) averaged over year.^x

Tillage	Stand	Yields
No tillage	26 a^z	4900 a
Disk-tillage fall and spring	28 a	4851 a
Disk-tillage fall only	27 a	4830 a

^x Years were 1994, 1995, and 1996.

^z Values followed by the same letter are not significantly different
(P < 0.05).

Stem rot, caused by Magnaporthe salvinii (Cattaneo) R. Krause & R. K. Webster (8), developed in plots in 1994, and the disease index (4) was similar for no tillage (4.25), disk-tillage fall and spring (4.05), and disk-tillage fall-only treatments (4.22). Diseases did not develop in these rice plots during 1995 and 1996, and insects were not a problem in plots during 1994-1996.

This is the first report on effects of tillage on stand and yield in a rice monoculture system. Wilson et al. (9) and Cartwright et al. (1) observed greater rice yields for tillage treatments compared with no tillage, but their experiments were conducted in a soybean-rice rotation system. A no-tillage system may or may not result in lower rice yields depending on the crop rotation program. The success of this system will probably depend on whether ruts were left in the field after harvest.

Cartwright et al. (1) demonstrated that rice yields were similar for fall-only tillage (stale seedbed) and fall and spring tillage (conventional tillage) treatments. Our data agree. A fall-only tillage system (stale seedbed) may be useful to some rice producers in the central USA because yields are similar to those in a conventional tillage system. Ruts in the field due to harvest equipment could be eliminated by fall tillage, and tillage in the spring would not be necessary prior to planting and application of a burn-down herbicide. The economics of a fall-only tillage or no tillage system may be similar to a fall and spring tillage system because the savings due to less tillage may be off set by the extra expense of burn-down herbicides applied prior to planting.

Acknowledgments

This work was, in part, supported by the Missouri Agriculture Experiment Station. This work was also supported by the rice check-off through the Missouri Rice Merchandising Council.

The authors thank Joyce Elrod for her efforts in this project and thank God for guidance.

Literature Cited

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5. National Crop Management Residue Survey. Online. Nat. Assoc. Conservation Districts. Lafayette, IN.

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8. Webster, R. K., and Gunnel, P. S., eds. 1992. Compendium of Rice Diseases. American Phytopathological Society, St. Paul, MN.

9. Wilson, C. E., Keisling, T. C., Miller, D. M., Dillion, C. R., Pearce, A. D., Frizzell, D. L., and Counce, P. A. 2000. Tillage influence on soluble salt movement in silt loam soils cropped to paddy rice. Soil Sci. Soc. Am. J. 64:1771-1776.

10. Wrather, J. A., Anderson, S. H., Wollenhaupt, N. C., Anand, S. C., and Kendig, S. R. 1993. Effects of tillage, row width, and cultivar on foliar diseases of double-crop soybean. Plant Dis. 77:1151-1152.

11. Wrather, J. A., Kendig, S. R., Anand, S. C., Niblack, T. L., and Smith, G. S. 1995. Effects of tillage, cultivar, and planting date on percentage of soybean leaves with symptoms of sudden death syndrome. Plant Dis. 79:560-562.

12. Wrather, J. A., Kendig, S. R., and Tyler, D. D. 1998. Tillage effects on Macrophomina phaseolina population density and soybean yield. Plant Dis. 82:247-250.