Improving Soil Quality to Increase Yield and Reduce Diseases in Organic Rice Production
We have completed our second year of this project to determine the impact of winter cover crops, soil amendments, and rice varieties on organic rice production at Beaumont, TX and Charleston, South Carolina. In Texas, the 2012-13 winter cover crops were established. The amounts of dry biomass were 4837 and 5907 kg/ha for clover and ryegrass, respectively. Compared with the previous season, the biomass of clover decreased significantly. It may be partially due to the delayed rain after planting in fall 2012. Cover crops had a similar effect on rice grain yield. Compared to the control, the 150 kg N/ha and 210 kg N/ha soil amendment rates increased rice grain yields. However, there was no difference in rice grain yields between the two N rates, indicating that 150 kg N/ha was sufficient for rice production in terms of N supply when land is managed in an organic system. Compared to Presidio and XL723, Tesanai had significantly higher grain yield and greater plant height. In addition, the severity of narrow brown leaf spot and brown spot was significantly higher (P ≤ 0.05) on Presidio and XL723 than on Tesanai. Under field conditions, cover crop treatments affected narrow brown leaf spot and brown spot with the most severe under fallow and least severe under clover. However, application of N did not affect the severity of narrow brown leaf spot and brown spot. Under greenhouse trials results were different from what was observed in the field as all the amendment rates of clover and ryegrass did not reduce the severity of narrow brown leaf spot compared to the untreated control. In South Carolina, a product, Serenade Max, was used to control diseases. The severity of narrow brown leaf spot was very low partially due to the disease control. As in TX, Tesanai had significantly higher yield than other cultivars (4426 kg/ha), followed by Presidio and XL723 which were not significantly different.
- Establishment of cover crop trials and determine the above ground biomass of clover and ryegrass at termination and their N content,
- Conduct field trial to determine cover crop, rice variety, and soil amendment application on organic rice production, grain yield, and milling quality, and
- Monitor the effects of cover crop, rice variety, and soil amendment application on rice disease occurrence.
- Establish an organic rice field testing site and expertise at the Clemson Coastal Research and Extension Center (CCREC),
- Evaluate yield potential of 6 rice varieties under organic management,
- Identify yield limiting production issues, and
- Compare results from the SC trial and previous trials in TX to determine how transferable results are between the two states.
Cover crop production: Two selected winter cover crops, Durana white clover and ryegrass, were planted on October 12, 2012. The dry fall delayed the germination of both cover crops. Both cover crops were terminated on March 7, 2013 and the fallow field of indigenous weeds, ryegrass, and some clover was cultivated. The amount of dry biomass at termination was 4380, 4837 and 5907 kg/ha for fallow, clover and ryegrass, respectively. Compared with the previous season, the yield of clover was lower, likely due to low soil moisture during seed germination. After termination, the cover crops were left for two weeks to decompose prior to incorporation. Our previous research has shown this is important to mitigate potential straighthead (physiological disease) occurrence in the subsequent organic rice crop.
Organic rice production: 1) Plot management: In the 2013 Beaumont field trials, we continued to examine cover crops (Durana white clover, ryegrass, and fallow), soil amendments (Nature Safe vs. Rhizogen) with three levels (untreated control, 150 kg N/ha, and 210 kg N/ha), and three rice varieties (Tesanai – high yield, used for flour market, Presidio – superior long grain quality, and XL723 – high yield, new released hybrid that was suggested by the Organic Rice Production Advisory Board) on rice production. Winter cover crop treatments served as main plots with rice varieties as sub-plots. Soil amendment treatments were applied as sub-sub-plots. Each treatment had four replications. Cover crops were managed as in the previous section. Soil amendments were broadcast by hand and incorporated just after planting using a rake in the drill-seeded plots that were approximately 5 m-2. Plots were flush irrigated to encourage uniform germination and after stand establishment were maintained under a flood until harvest to help with weed control. In addition, we treated all the seed with OMRI certified gibberellic acid (GA) to promote seed germination. Organic rice was drill seeded on April 22, 2013 using a high seeding rate (160 kg/ha for Presidio and Tesanai, and 80 kg/ha for XL723 which is double the recommended rate for hybrids). Although the three varieties emerged on the same date, compared to Presidio and XL723, Tesanai had longer growth duration and matured two or more weeks later. All plots were harvested by hand as they came to maturity, in early August for Presidio and XL723 and in late August for Tesanai. 2) Effects of cover crop, variety, and soil amendments on organic rice grain yield and milling quality: The winter cover crops when averaged over all soil amendment treatments did not significantly affect the main crop (MC) grain yields in 2013 (Fig. 1). The average MC grain yields were 7443, 7292, and 7312 kg/ha for clover, ryegrass, and fallow treatments, respectively. Our two-year studies indicated that ryegrass and clover had the same effect on organic rice production in southern USA.
Rice variety had a significant effect on MC grain yield. Tesanai had higher MC yield than XL 723 and Presidio (Fig. 2). Grain yield using Nature Safe was similar to that with Rhizogen, indicating that both were equally effective in providing nutrients for organic rice production. However, the application rate of soil amendments significantly affected rice grain yield. Compared to the control (0 applied), both the 150 kg N/ha and 210 kg N/ha soil amendment application rate increased rice grain yields by 6%. There was no difference in rice grain yields between the two N rates, indicating that 150 kg N/ha was sufficient for organic rice production in terms of N supply. Plant height decreased in the order of Tesanai, XL723, and Presidio. Although taller varieties would be expected to have an advantage in weed competition, the weed density was very low in 2013 organic rice trials.
Rice milling yield of MC was significantly affected by cover crop and rice variety. Higher milling quality (whole grain yield) was observed with the ryegrass treatment than with clover and fallow. Also, the highest milling yield was with Presidio and lowest with Tesanai.
To our knowledge, no study has been reported on the potential of ratooning in an organic rice system. In 2013, we tested rice ratoon potential (harvest of a second crop following regrowth from the crop’s stubble) and our preliminary results indicated that organic rice ratooning was promising if the crops were planted in a timely manner. In addition, we collected water samples during rice production and soil samples (288) after rice ratoon crop harvesting. Such soil samples have been dried and ready for analysis and incubation trials.
Field Studies: A trial was established in a field under organic management at Beaumont, TX in 2013 to evaluate the effects of cover crops, rice cultivars, and soil fertilizer amendments on severity of narrow brown leaf pot, brown spot, and straighthead. Cover crop treatments significantly affected the severity of narrow brown leaf spot and brown spot on Presidio (Fig. 3) but not on the more resistant Tesanai (Fig. 4) and XL723 (Fig. 5). The severity of narrow brown leaf spot and brown spot was lowest in the clover cover crop treatment and highest in the fallow treatment (Fig. 3). Severity of narrow brown leaf spot was significantly lower (P ≤ 0.05) on Tesanai and XL723 than on Presidio. Both Presidio and XL723 had a similar but higher levels of brown spot compared to Tesanai. The fertilizers, NatureSafe and Rhizogen, did not affect severity of both narrow brown leaf spot and brown spot. Application of N at either 150 or 210 kg/ha did not significantly affect severity of narrow brown leaf spot and brown spot either. No symptoms of straighthead were observed in plots with any cover crop treatments including fallow.
The results of this field study indicate that use of resistant cultivars such as Tesanai and XL723 and clover cover crop was effective in reducing narrow brown leaf spot and brown spot. When growing a more susceptible cultivar like Presidio, a cover crop was effective in reducing the level of disease as compared to the fallow treatment.
Greenhouse Studies: Two greenhouse assays were conducted to evaluate if cover crop-amended soils can induce systemic resistance against narrow brown leaf spot and enhance the growth of rice plants.
Field plot soils incorporated with cover crops: Soil samples were randomly collected prior to planting of the 2013 rice crop and after the winter cover crops had been terminated in the fallow, clover, and ryegrass fields. Presidio was seeded into 5.1-cm pots filled with the soil samples in the greenhouse. At 4 weeks after seeding, rice seedlings were inoculated with the narrow brown leaf spot pathogen and disease severity was rated at 4 weeks after inoculation. Plant height and dry above ground biomass were measured 4 weeks after seeding and at maturity, respectively.
Clover and ryegrass amendment treatments did not reduce the severity of narrow brown leaf spot compared to fallow control treatment (Table 1). Both cover crop treatments did not improve plant height either. However, both cover crop treatments significantly increased dry above ground plant biomass with clover cover crop treatment being more effective than ryegrass cover crop treatment. Unlike the field trials, the results of this greenhouse assay indicate that field soils incorporated with clover or ryegrass cover crop did not induce resistance to narrow brown leaf spot but enhanced plant growth.
Cover crop amendment rate effects: Ground powder of clover and ryegrass was incorporated at 0, 0.2, 0.8, and 3.2 % (wt/wt, approximately equivalent to 0, 2, 8, and 32 tons of fresh above ground biomass per acre) into soil collected from a field that had been in fallow-rice organic management for many years. Presidio was seeded into the treated soils and the narrow brown leaf spot pathogen was inoculated as described above. Disease severity and plant growth parameters (plant height and dry above ground biomass) were measured as described before.
All the amendment rates of clover and ryegrass did not reduce the severity of narrow brown leaf spot compared to the untreated control (Table 2). However, either clover or ryegrass at 3.2% significantly increased plant height and dry above ground biomass compared to the untreated control. The results of this amendment rate study are in agreement with the results of the field plot soil amendment study conducted in the greenhouse, indicating that soil amendment with a high rate of clover or ryegrass could improve rice plant growth but did not induce resistance against narrow brown leaf spot. The differences in disease control between the field and greenhouse study could be a result of other factors impacting the development of the disease in the field versus the greenhouse where al plants were artificially inoculated.
Summaries of other relevant studies at Beaumont
Data from previous organic trials to determine the agronomic performance of rice cultivars grown under organic and conventional field management were summarized. Research was conducted in Beaumont, TX over 3 years and evaluated 14 rice cultivars that included medium and long grains, aromatics, and allelopathic germplasm. The organic studies were conducted on certified organic land following a winter cover crop (white clover) that was plowed down in the spring followed by application of 1680 kg/ha of Nature Safe (13-0-0; made from feather, meat, and blood meal) applied at planting. The conventional fields were fallowed for two years and then drill seeded with 224 kg/ha of urea applied in a three way split. The experimental design consisted of a RCB with four replications. Data were collected on plant stand, heading, height, days to harvest, grainfill duration, yield, and total and whole milling yield.
The main effects year, cultural management, and variety were significantly different for essentially all traits, as were their interactions. As had been seen in previous studies, rice grown under the organic system had reduced plant stands, earlier days to heading and maturity, a shorter grainfill period, and shorter plant height as compared to conventional management. Although there was no significant difference in head rice yields, organic management had significantly higher field yield and total milling yield than the conventional system. The higher yield under organic conditions was particularly noticeable in the third year and may be a result of the cumulative impact of three years of green manure cropping (clover). There were few significant correlations among the agronomic traits measured under the conventional system. However, under organic management, yield was positively correlated with maturity, height, and grainfill (r= 0.54, 0.76, 0.43, respectively). Thus cultivars that have a larger plant (source) and longer duration of grainfill (sink) had higher yield potential under the organic system, possibly related to the slow release of organic fertilizer. This indicates that cultural management factors that enhance biomass during the growing season may also increase yield potential.
Charleston, South Carolina
The field at CCREC-ORF that had been under organic management for a number of years was planted with certified organic annual rye grass, Lolium multiflorumat 168 kg/ha in the fall 2012. One month before rice seeding on April 1st, 2013, the annual rye grass was mowed and tilled into the soil to prevent allelopathic effects on the rice germination. Soil samples were taken on April 14th, 2013. Fertilizer consisted of Nature Safe 8-5-5 broadcast at 179 Units N/ha and tilled into the soil profile. The study included six varieties; Tesanai, Presidio, and XL723, common to the TX study, and Carolina Gold, Charleston Gold, and IAC 600 of particular interest for organic production in SC. The study was laid out in a completely random design with four replications. Seed from each variety was pre-soaked and allowed to pip (germinate) prior to hand seeding into the flooded field on May 9. Each plot was surrounded by metal flashing to prevent movement of the seed and soil amendment into adjacent plots. The field was drained and the pre-germinated seed was allowed to peg into the wet soil prior to re-flooding. During the season days to heading, plant height, and days to harvest were recorded. Unlike the prior year in 2012, in 2013 we applied Serenade Max (Bacillus subtilis.strain QST 713) for disease control.At harvest a 0.93 m2 area was hand harvested within each replication and subjectively graded for disease and physiological disorders. As in TX, Tesanai had significantly higher yield than other cultivars (4426 kg/ha), followed by Presidio and XL723 which were not significantly different. Although these varieties are suited to high value niche markets, Charleston Gold, Carolina Gold, and IAC 600 were the lowest yielding in the trial. Weed and disease pressure were not high, however more weeds were observed in the shorter varieties Presidio and IAC 600.
- Fig.4. Effects of cover crops on the severity of narrow brown leaf spot (NBLS) and brown spot on Tesanai in 2013.
- Fig.5. Effects of cover crops on the severity of narrow brown leaf spot (NBLS) and brown spot on XL723 in 2013.
- Table 1. Effects of field plot-incorporated clover and ryegrass cover crops on the severity of narrow brown leaf spot (NBLS) and the growth of rice plants in the greenhouse.
- Table 2. Effects of different amendment rates of clover and ryegrass on the severity of narrow brown leaf spot (NBLS) and the growth of rice plants in the greenhouse.
- Table 3. The difference in rice production between organic and conventional systems.
- Photo 1. Organic Rice Field
- Photo 2. Durana Clover
- Fig. 2. Effect of rice variety on main crop yield.
- Photo 3. Ryegrass
- Fig.3. Effects of cover crops on the severity of narrow brown leaf spot (NBLS) and brown spot on Presidio in 2013.
- Fig. 1. Effect of winter cover crop on rice main crop yields.
Impacts and Contributions/Outcomes
Our results have been presented at scientific conferences, field days, and extension meetings. During our 2013 field day, an organic rice tour at the Texas A&M AgriLife Research Center at Beaumont attracted more than fifty (50) rice producers, county agents, millers, industrial consultants, and researchers. In the 2013 ASA-SSSA-CSA annual meeting, the PI gave a talk on organic rice production which attracted more than forty (40) in the audience. Additional presentations were made by all PI’s at the Rice Technical Working Group meeting in February 2014. In addition, Floyd Garrett, a high school student, participated this program for his intern training to gain experience in sustainable agriculture and presented a poster to the S-SARE.
- Dou, F., A. McClung, and S. Zhou. 2013. The impacts of soil amendments on organic rice production (oral presentation). Annual Meeting of the Soil Science Society of America. Tampa, FL. November 2013.
- Dou, F., A. McClung, and S. Zhou. 2013. Integrating choice of variety, soil amendments and cover crops to optimize organic rice production. Texas Rice Special Section.
- Dou, F. 2013. Improving soil quality to increase yield and reduce diseases in organic rice production (oral presentation). 2013 Organic Rice Workshop, Houston, TX.
- Dou, F. 2013. Improving soil quality to increase yield in organic rice production (poster). Field Day. Eagle Lake, TX.
- Dou, F. 2013. Improving soil quality to increase yield in organic rice production (poster). Field Day. Beaumont, TX.
- Dou, F., S. Zhou, A. McClung, J. Storlien, Y. Lang, A. Torbert, F. Hons, B. Ward, S. Kresovich, and J. Wight. 2014. Cover crop, soil amendments, and variety effects on organic rice production in Texas (oral presentation). 35rd Rice Technical Working Group Meeting. New Orleans, LA. February, 2014.
- Zhou, X. G., F. Dou, and A. M. McClung. 2013. Effects of cover crops, fertility, cultivars, and biocontrol agents on organic rice diseases. Organic Rice Advisory Meeting. Mar. 20. 2013. Houston, Texas, USA.
- Zhou, X.G. 2013. Organic rice disease management. Pages 56-59. 2014 Texas Rice Production Guidelines. Texas AgriLife Research and Texas AgriLife Extension. B-6131. https://beaumont. tamu. edu/eLibrary/Bulletins/2014_Rice_Production_Guidelines. pdf.
- Garrett, T.F. and F. Dou. 2013. SARE. Learning experience of organic rice production. 2013 Southern SARE Young Scholar Enhancement Program.
- McClung, A.M., Duke, S., and Chaney, R.L. 2014. Impact of Organic Production Management on Variety Yield and Grain Arsenic Accumulation. 35rd Rice Technical Working Group Meeting. New Orleans, LA. February, 2014.
Supervisory Research Geneticist
USDA ARS Dale Bumpers National Rice Research Center
2890 Hwy 130 E
Stuttgart, AR 72160
Office Phone: 8706729300
Research Specialist III
Clemson University Department of Horticulture
2700 Savannah Hwy
Charleston, SC 29414
Office Phone: 8434025399
Professor and Extension Economist
Texas A&M University
Department of Agricultural Economics
College Station, TX 77843-2124
Office Phone: 9798451772
Texas A&M AgriLife Research & Extension Center at Beaumont
1509 Aggie Dr.
Beaumont, TX 77713
Office Phone: 4097522741
University of South Carolina
715 Sumter Street
Columbia, SC 29208
Office Phone: 8037773806