Improving Soil Quality to Increase Yield and Reduce Diseases in Organic Rice Production

Improving Soil Quality to Increase Yield and Reduce Diseases in Organic Rice Production

Summary

We have completed our first 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 2011-12 winter cover crops were established successfully with full coverage. The amount of dry biomass were 4690 and 5157 lb/acre for clover and ryegrass, respectively. Plots were cultivated and drill seeded but high weed pressure in the fallow plots resulted in very poor stands. Only results of rice grain yields from clover and ryegrass treatments were presented. Cover crops had a similar effect on rice grain yield, although numerically, rice grain yield under ryegrass treatment was higher than that under clover treatment. Compared to Presidio, Tesanai had significantly higher grain yield. Soil amendments did not have significant effect on rice grain yield. Compared to the control, the 150 lb N/acre and 210 lb N/acre soil amendment rates increased rice grain yields by 11%. There was no difference in rice grain yields between the two N rates, indicating that 150 lb N/acre was sufficient for organic rice production in terms of N supply. Compared to Presidio, Tesanai had greater plant height and appeared to be more competitive with weeds. Aboveground biomass of the rice crop was affected by the rate of soil amendments rather than the type of soil amendments. Rice milling yield was significantly affected by cover crop and rice variety. Severity of narrow brown leaf spot was significantly higher (P ? 0.05) on Presidio than on Tesanai while severity of brown spot was low on both cultivars. Cover crop treatments did not affect narrow brown leaf spot. However, clover cover crop treatment had significantly lower brown spot severity compared to the winter fallow and ryegrass treatments. Application of N at either 150 or 210 lbs/acre was effective in reducing the severity of narrow brown leaf spot and brown spot as compared to the control. Severity of either disease linearly (R2 ? 0.56) decreased with increased N level. In addition, no symptoms of straighthead were observed in any plots. In South Carolina, prior to harvest, evidence of sheath rot (Sarocladium oryzae) and brown spot (Cochliobolus miyabeanus) diseases and rice water weevil (Lissorhoptrus oryzophilus Kuschel) symptoms were noted. Brown spot and sheath rot were most prevalent in the Charleston Gold and the IAC 600 whereas straighthead was more of a problem in the Carolina Gold and Charleston Gold. The highest yielding cultivars were Tesanai and Presidio.

Objectives/Performance Targets

1. 1. Establishment of cover crop trials and determine the aboveground biomass of clover and ryegrass at termination and their N content,
   2. Conduct field trial to determine cover crop, rice variety, and soil amendment application on organic rice production, grain yield, and milling quality, and
   3. Monitor the effects of cover crop, rice variety, and soil amendment application on rice disease occurrence.

1. 1. Establish an organic rice field testing site and expertise at the Clemson Coastal Research and Extension Center (CCREC),
   2. Evaluate yield potential of 6 rice varieties under organic management,
   3. Identify yield limiting production issues, and
   4. Compare results from the SC trial and previous trials in TX to determine how transferable results are between the two states.

Accomplishments/Milestones

Cover crop production: Two selected winter cover crops, Durana white clover and ryegrass, were planted on November 1, 2011. The winter cover crops were established successfully with full coverage. Both cover crops were terminated on April 14, 2012. The amount of dry biomass at termination were 4690 and 5157 lb/acre for clover and ryegrass, respectively. After termination, the cover crop biomass was left for another week to decompose prior to incorporation, which is important to mitigate potential straighthead (physiological disease) occurrence in the subsequent organic rice crop. The fallow field had indigenous weeds, ryegrass, and some clover prior to cultivating.
Organic rice production: 1) Plot management: Organic rice was drill seeded on May 1, 2012 using a high seeding rate. Although both varieties emerged on the same date, compared to Presidio, 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 late August to early September for Tesanai. 2) Effects of cover crop, variety, and soil amendments on organic rice grain yield and milling quality: In the 2012 Beaumont field trials, we examined cover crops (Durana white clover, ryegrass, and fallow), soil amendments (Nature Safe vs. Rhizogen) with three levels (untreated control, 150 lb N/acre, and 210 lb N/acre, and two rice varieties (Tesanai – high yield, used for flour market vs. Presidio – superior long grain quality) 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 applied and incorporated just after planting the rice in drill-seeded plots approximately 5 m-2. Plots were flush irrigated to encourage uniform germination and were maintained under a flood until harvest to help weed control.
Plots planted in the fallow field had very poor stands due to severe weed pressure. Therefore, the only results of rice grain yields were from the clover and ryegrass treatments. Although numerically, rice grain yield following the ryegrass cover was higher than that under clover treatment, although the difference was not significant.
Rice varieties were different for grain yield with Tesanai having significantly higher grain yield than Presidio. The grain yield of Tesanai was 75% higher than that of Presidio. Similar to cover crops, soil amendments did not have significant effect on rice grain yield. The 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 lb N/acre and 210 lb N/acre soil amendment application rate increased rice grain yields by 11%. There was no difference in rice grain yields between the two N rates, indicating that 150 lb N/acre was sufficient for organic rice production in terms of N supply.
Both cover crop and variety did not affect rice seedling establishment. Compared to Presidio, Tesanai had higher plant height. The weed density under Presidio was greater than that under Tesanai, indicating that greater weed competition with Presidio.
Aboveground biomass of the rice crop was affected by the rate of soil amendments rather than the type of soil amendments. Compared to the control, application of soil amendments significantly increased aboveground biomass. Also, the aboveground biomass was highly correlated with the corresponding grain yield.
Rice milling yield was significantly affected by cover crop and rice variety. Higher milling quality (whole grain yield) was observed with the ryegrass treatment than with clover. Also, Presidio had higher milling quality than Tesanai.
Disease monitoring: The effects of rice cultivars, cover crops and soil amendments on severity of narrow brown leaf spot (NBLS), brown spot (BS), and straighthead were also investigated in the same field trial as for organic rice production at Beaumont. Severity of NBLS was significantly higher (P ? 0.05) on Presidio than on Tesanai while severity of BS was similarly low for both cultivars. These results indicate that Presidio was very susceptible to NBLS and Tesanai was resistant in this organic rice production system, which is in agreement with our previous studies. Cover crop treatments did not affect NBLS. However, the clover cover crop treatment had a significantly lower BS severity compared to the winter fallow and ryegrass treatments. Neither fertilizer, NatureSafe or Rhizogen, affected the severity of NBLS or BS symptoms. Application of N at either 150 or 210 lbs/acre was effective in reducing severity of NBLS and BS as compared to the control. Severity of either disease linearly (R2 ? 0.56) decreased with the increased N rate applied. In addition, no symptoms of straighthead were observed in any plots.

Over the last 20 years there has been increasing interest in re-establishing rice production in South Carolina for the primary purpose of supporting the local food market. Currently there are some 600-700 ac of conventional rice production with an additional ~150 ac in organic. However there is essentially no local research to support these operations, thus this research was undertaken to test findings from the Texas environment in South Carolina.
The field at CCREC had been planted to Dixie Crimson Clover in fall 2011. In April 2012 the cover crop was terminated and disked three times prior to the levees being pulled in mid-April. Fertilizer consisted of Nature Safe 13-0-0 broadcast at 1,000 lbs /Ac and worked into the soil profile with a Perfecta II field cultivator. Field plots for each of 6 varieties were laid out as unreplicated strips approximately 9.75 m2. Each plot was encompassed by metal flashing and the field was flooded. Seed from each variety was pre-soaked and allowed to pip (germinate) prior to hand seeding into the flooded strip plot on May 7. 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. At harvest a 0.93 m2 area was hand harvested in three areas within each strip. Samples were air dried in a greenhouse then grain moisture and grain yield were determined. Rough rice samples were sent to AR where 125 g samples from each replicate were used for milling determination using a McGill No. 2 miller.
Prior to harvest, evidence of sheath rot (Sarocladium oryzae) and brown spot (Cochliobolus miyabeanus) diseases and rice water weevil (Lissorhoptrus oryzophilus Kuschel) symptoms were noted. Brown spot and sheath rot were most prevalent in the Charleston Gold and the IAC 600 whereas straighthead was more of a problem in the Carolina Gold and Charleston Gold. Some brown spot was also observed in the STG 06L-35-061 and Presidio but not as severe.
The highest yielding cultivars were Tesanai and Presidio. The variety STG 06L-35-061 is a new germplasm release derived from allelopathic cultivars PI31277 and PI338046. The other three varieties are for specialty markets: IAC600 -purple aromatic, Charleston Gold -long grain aromatic, and Carolina Gold -heirloom variety; the latter two are currently being grown commercially in South Carolina. These results indicate that there is significant room for improvement in yield potential, maturity, and height based upon choice of cultivars for production in South Carolina. However, varieties must also have grain quality traits suitable for local markets. Milling yield was extremely low for all varieties and was attributed to overdrying the samples in the greenhouse.
The 2012 South Carolina results were also compared with two years of data from Texas. Although STG 06L-35-061 had not been grown in Texas before, two of its parents, PI31277 and PI338046, had been and were averaged for general comparison. Although the magnitude was different between yields of the varieties at the two locations, the ranking was very similar.

• Durana Clover
• Tesanai
• Field plots
• Ryegrass

Impacts and Contributions/Outcomes

The PI’s met in Beaumont to discuss the project objectives, goals and formulate specific actions and activities. Two posters were presented at Eagle Lake rice field day and Beaumont field day in 2012. One research highlight on our organic rice project has been published in the special Texas Rice Newsletter which was distributed to more than 200 rice growers who attended those rice field days as well as being available on the web. Also, we set up a field tour to visit our organic rice field plots. After that, a workshop was held to discuss the research needs and main concerns from local organic rice industry. For example, what options are available for organic seed treatment? Visitors learned about different cover crops and principles of establishment. In the late summer, we visited county agents and organic rice producers to introduce the SSARE organic rice project and the expected outcomes for nutrient and weed management. Results from the 2012 studies were presented at the Advisory Board meeting March 20, 2013 and plans for 2013 trials and ongoing outreach and extension efforts were discussed.

Collaborators: