Progress report for LS22-364
Project Information
Demand for organic rice has led to an almost six-fold increase since 1995 in organic rice production in the US. Texas and California are the largest organic rice producing states, accounting for more than 76% of the acreage. Most conventional and organic rice growers in Texas produce a second crop, also known as a ratoon crop, as a result of the relatively low input costs and high profitability. Previous research has led to improvements in main crop organic rice production, but data on how to optimize ratoon crop organic rice nutrient management and assess sustainability are sorely lacking. Developing economically and environmentally sustainable practices is critical to further expansion of organic rice production in the US. We propose to conduct comprehensive field experiments to assess the effects of cultivars, cover crops, and nitrogen rates on ratoon crop rice yields, milling quality, pest pressures, environmental sustainability, and economic viability. On-farm demonstrations with collaborating organic and conventional rice producers will compare economic and environmental metrics achieved using current grower practices with those achieved using recommended best management practices (BMPs) developed through the proposed research. The outcome of this project will improve the economic and environmental sustainability of organic rice production by providing tested and verified BMPs for the southern US. This project addresses two SARE high priority Project Areas ‘Organic Farming Systems’ and ‘“Environmentally Sound Practices’.
The overall goal of this proposal is to evaluate effects of cultivars, cover crops and ratoon N fertilizer rates on organic ratoon rice production in the Southern US. Environmental sustainability through integrated life cycle analysis of organic rice ratooning will also help growers to fine tune their best management practices, which will improve the environmental quality. The proposal has four specific objectives
-
- Determine the effects of cultivars, cover crops and ratoon N rates on organic main and ratoon crop rice yields, milling quality, and pest pressures.
- Evaluate environmental sustainability and soil health of organic main and ratoon crop production systems compared to that of conventional rice production.
- Develop best management practices (BMPs) for main and ratoon crop organic rice production systems.
- Disseminate BMPs on the production potential and economic viability through on-farm demonstrations, field day tours and workshops.
Cooperators
Research
Experimental Site:
In 2023, a field experiment was conducted in Beaumont, TX (30.07°N, 94.28°W). The experimental site is characterized by heavy clay soil and high annual average rainfall (> 1,600 mm) suitable for rice cultivation. The monthly mean air temperature and total rainfall during the cropping season are presented in Fig. 1. Briefly, monthly mean air temperature ranged from 20.0 to 31.5 °C with an average of 26.4 °C. Total precipitation during the growing season was 600 mm. The field soil is classified as Morey silt loam (fine-silty, siliceous, superactive, hyperthermic Oxyaquic Argiudolls) and contains an average of 680, 156, and 116 g kg-1 for clay, sand, and silt, respectively. The soil has a pH of 6.7 (1:2 soil/water), an electrical conductivity of 12.63 µS cm-1.
Fig. 1: Monthly average air temperature (oC) and total precipitation (mm) at the experimental site during the growing season in 2023
Experimental Design:
The factorial experiment was arranged in a randomized complete block design (RCBD) with four replications. The three main experimental factors are rotation (white clover vs winter fallow as a control), rice cultivar [an inbred, Presidio and a hybrid. XP753 (RiceTec, Inc., Alvin, TX)] and N fertilization rate for ratoon crop (untreated control, 30, 60, 90, 120 kg N ha-1) applied using Nature Safe. Cover crop treatments were applied as main plots with two rice cultivars as subplots. Ratoon N rates were applied as sub-sub-plots.
Cover Crop and Rice Culture:
In the fall of 2022, the rice field was prepared through repeated cultivation and laser leveling. Subsequently, the levee and cross levee were pulled on October 6th, 2022, to establish four blocks. On October 12th, 2022, white clover (Trifolium repens) seeds were manually spread using a belly spreader at a rate of 7 kg ha-1 (Fig. 1 A). The seeds were pre-inoculated with rhizobium strains that were specific to white clover. Despite our efforts, including repeated planting on December 6th, 2022, and January 4th, 2023, the growth and establishment of the cover crop was poor due to the wet and cold winter conditions. To simulate the effects of the cover crop, alfalfa (Medicago sativa) hay was applied to half of each block on March 6th, 2023 (Fig. 1 B&C). The hay was applied at a rate of 7 Mg ha-1 on an oven-dry matter basis. After the hay application, each block was cultivated several times to either incorporate the hay into the soil or to eliminate the emerged weeds.
Plots were drill-seeded on 31st March 2023. Immediately after seeding, plots were irrigated for 24 h to promote uniform seedling emergence, and then drained to allow oxygen permeation and emergence. After full emergence, the field was reflooded to 8 to 10 cm (to allow 1/3 to 1/2 of the seedling height to remain above the water) and the flood was maintained throughout the growing season for plant growth and weed suppression. Organic N fertilizer (13.0% N, 0% P2O5, 0% K2O; Nature Safe) was manually applied at a rate of 140 kg N ha-1 to each plot at the 4-leaf stage on May 5th 2023. Due to the breakdown of machine harvester, plots were hand harvested during July 26-28, 2023. Before main crop harvesting, ratoon N treatment treatments (untreated control, 30, 60, 90, 120 kg N ha-1) were applied on July 17th, 2023. A permanent reflood was established on August 8th, 2023, and continue to maintain until 15 days before ratoon crop was harvested. On October 25, ratoon crop was machine harvested (Massey Ferguson 8XP research combine, Kincaid equipment manufacturing, Heaven, TX).
Observations and Measurements:
In this study, several agronomic traits, soil fertility, weed, diseases and insect pressure were assessed, including plant height, grain yield, milling quality, grain nitrogen (N) content, soil nitrogen availability, soil microbial biomass, weed pressure, diseases, and insect incidents.
Plant Height:
Plant height was measured from the ground to the tip of the flag leaf. Measurements were taken for ten randomly selected plants from four inner rows for both the main and ratoon crop.
Grain Yield and Moisture Content:
For rice harvested, grain moisture content was determined using a GAC® 2100 grain analyzer (DICKEY-john Corporation, Auburn, IL). Grain yield (kg ha-1) was adjusted to a storage moisture content of 12%.
Grain Milling Quality:
Rough grain samples (100 grams) were processed using a rice mill (Industrias Machina Zaccaria S/A, São Paulo, Brazil) for 74 seconds to separate hulls and grains, and to distinguish whole milled grains from broken ones. Total grain milling yield (%) was calculated as the weight of whole and broken milled grains divided by the total weight of rough rice, while whole grain milling yield (%) was determined as the weight of whole grains divided by the total weight of whole and broken grains.
Grain Nitrogen Content:
Total grain nitrogen was estimated from 120 mg subsamples using the Dumas complete combustion thermal conductivity method (LECO FP-528, St Joseph, MI, USA) [Horneck and Miller, 1998].
Weed Pressure:
Weed pressure was estimated visually and reported as a percentage of the plot area infected by weed biomass.
Soil Nitrogen Availability:
Surface soil samples (0-25 cm) were collected and extracted with 0.5 K2SO4. The soil extract was used to extractable mineral N using a discreate analyzer (AQ300, Seal Analytical, Inc. Wisconsin) (Li et al., 2012).
Diseases and Insect Incidents:
Weed density was measured by estimating % of area of plot infested by weeds by human observation. Narrow brown leaf spot and brown leaf spot infestation were assessed on a scale from 0 to 9, with 0 indicating no effect and 9 indicating maximum impact. Rice water weevil infestation was assessed by counting white heads on a whole-plot basis.
Data Analysis:
The PROC GLM procedure of SAS 9.4 (SAS Institute Inc., Cary, NC) was used for data analysis. Rotation and rice cultivar were considered as categorical variables; nitrogen rates for ratoon crop were considered as a continuous variable; and replication was considered as a random factor. All significant treatment effects were determined using the Differences of Least Squares Means (LSMEANS) at p ≤ 0.05. The CORR procedure was used to calculate the Pearson’s Correlation (r) between variables, and p ≤ 0.05 was considered as significant.
Main Crop
Agronomic traits:
The analysis of variance (ANOVA) for agronomic traits, including plant height, grain yield, total grain milling yield, whole grain milling yield, grain nitrogen (N) content, and total N removal, is presented in Table 1. Both rotation and cultivar significantly influenced plant height, grain yield, and N removal. Cultivar had a significant impact on the milling quality of the main crop, while rotation influenced grain N content. However, the interaction effect of cover crop and cultivar was not significant for any of the measured agronomic traits.
Cover cropping resulted in a 3.8% increase in plant height and a remarkable 46% increase in grain yield (Fig 2A & B). Similarly, cultivar XP753 exhibited a 26% increase in plant height and a substantial 75% increase in grain yield. As a result, hybrid cultivar XP753 demonstrated higher total (3.2%) and whole (20%) grain milling yield compared to inbred cultivar Presidio (refer to Fig 2C & D). Interestingly, cultivar did not have any effect on grain N content, whereas cover cropping increased grain N content by 5.0% compared to winter fallow (Fig 2E). Total N removal was calculated by multiplying grain yield with N content. As expected, both cover crop and XP753 removed 54% and 73% more N compared to either winter fallow or Presidio, respectively (Fig 2F).
These findings highlight the significant influence of cover crop and cultivar selection on various agronomic traits, emphasizing the potential for optimizing agricultural practices to enhance productivity and nutrient management.
Table 1: Results of analysis of variance (ANOVA) for agronomic traits of main crop
|
Source |
DF |
Probability |
|||||
|
Plant Height |
Grain Yield |
Total grain milling yield |
Whole grain milling yield |
Grain N content |
Total N removal |
||
|
Cover Crop (CC) |
1 |
0.0230 |
0.0002 |
0.3236 |
0.2896 |
0.0030 |
<0.001 |
|
Cultivar |
1 |
<0.0001 |
<0.0001 |
0.0002 |
<0.001 |
0.1271 |
<0.001 |
|
CC*Cultivar |
1 |
0.9190 |
0.2266 |
0.7116 |
0.1441 |
0.1537 |
0.1337 |
Soil N availability:
Soil nitrogen (N) availability was assessed during the active tillering and panicle initiation stages, conducted in early May and late July respectively. It was observed that during the early stages of the season, the presence of cover crops led to an increase in N availability compared to plots with winter fallow. However, this positive effect gradually diminished as the crop progressed towards the panicle initiation stage in late July. One plausible explanation for the lack of distinguishable differences in N availability after May 5th is the application of a blanket dose of 145 kg N ha-1 to all plots, regardless of treatment, using Nature Safe®. This uniform application of nitrogen may have obscured the potential effects of the cover crop treatment on soil N availability (Fig 3). Interestingly, the choice of cultivar did not exhibit any discernible impact on soil N availability during either the early or late stages of the crop growing season.
Weed pressure:
In organic cultivation, effective weed management is crucial, presenting a formidable challenge. This is especially pronounced in organic rice cultivation, where weed control is pivotal for crop success. Weed infestation levels during the main rice crop phase exhibited significant variability, ranging from minimal occurrences to extensive infestations across the plots. Consistent with findings in existing literature, the present study also underscores a notable negative correlation between weed pressure and organic rice main crop grain yield (Fig 4). This correlation highlights the importance of implementing effective weed management strategies to mitigate adverse impacts on crop productivity. By recognizing and addressing the detrimental effects of weed pressure, organic rice farmers can enhance the likelihood of achieving optimal yields and ensuring successful crop outcomes. This emphasizes the critical role that weed management plays in the context of organic rice cultivation.
Ratoon Crop
Agronomic traits:
The ANOVA results presented in Table 2 reveal significant effects of rotation and cultivar on ratoon plant height and grain yield. The most significant result was the effect of nitrogen rates on ratoon rice yield, which is particularly noteworthy given its significance level at P=0.05. Notably, total grain milling yield was solely influenced by rotation, while whole grain milling yield was affected by both rotation and cultivar. Among the agronomic traits, nitrogen application rates to the ratoon crop impacted grain N content and N removal. Additionally, grain N content was influenced by cultivar, while total N removal was affected by both rotation and cultivar. Importantly, none of the interactive effects were found to be significant for any of the agronomic traits, except for plant height, which was influenced by the interaction of rotation and cultivar.
Table 2: Results of analysis of variance (ANOVA) for agronomic traits of ratoon crop
|
Source |
DF |
Probability |
|||||
|
Plant Height |
Grain Yield |
Total grain milling yield |
Whole grain milling yield |
Grain N content |
Total N removal |
||
|
Rotation (R) |
1 |
<0.0001 |
0.0007 |
0.0311 |
<0.0001 |
0.6960 |
0.0007 |
|
Cultivar (C) |
1 |
<0.0001 |
<0.0001 |
0.1113 |
<0.0084 |
0.0003 |
<0.0001 |
|
Nitrogen rate (N) |
4 |
0.6466 |
0.0526 |
0.8016 |
0.8939 |
0.0021 |
0.0049 |
|
R*C |
1 |
0.0181 |
0.8572 |
0.4827 |
0.3505 |
0.1751 |
0.6721 |
|
R*N |
4 |
0.6193 |
0.8703 |
0.5095 |
0.9611 |
0.9644 |
0.9200 |
|
C*N |
4 |
0.9673 |
0.7818 |
0.5035 |
0.3584 |
0.8009 |
0.4654 |
|
R*C*N |
4 |
0.8786 |
0.6969 |
0.4587 |
0.5984 |
0.3266 |
0.5602 |
Cover cropping resulted in a 6.1% increase in plant height and a remarkable 34% increase in grain yield, as shown in Figure 5 A and 5B, respectively. Similarly, cultivar XP753 exhibited an 11% increase in plant height and a substantial 97% increase in grain yield. Surprisingly, cover cropping led to a 1.0% increase in total grain milling yield. Consequently, hybrid cultivar XP753 demonstrated higher whole grain milling yield (5.5%) compared to inbred cultivar Presidio, while cover cropping increased whole grain milling yield by 11% (Fig 5 C and D). Interestingly, rotation did not have any effect on grain N content. However, XP753 exhibited an 8.4% increase in grain N content compared to Presidio (Fig 5 E). As expected, both cover crop and XP753 removed 34% and 115% more N compared to either winter fallow or Presidio, respectively (Fig 5 F).
The impact of nitrogen (N) rates on grain yield, N content, and N removal is presented in Figures 6 A, B, and C. The increase in N application rates corresponded with an increase in ratoon yield, reaching a peak at 101 kg N ha-1 and 135 kg ha-1 after stabilizing from 0 to 68 kg N ha-1. The highest yield of 2.0 Mg ha-1 was observed for the 101 kg N ha-1, followed by the 135 kg N ha-1, although statistically similar, both significantly surpassed the yield obtained from 0 kg N ha-1. Interestingly, the 101 kg N ha-1 treatment exhibited lower grain N content compared to 34,68 or 153 kg N ha-1, but was statistically similar. Similarly, the pattern observed for N removal mirrored that of grain yield, with the greatest N removal of 34 kg ha-1 recorded for the 101 kg N ha-1 treatment, comparable to the 135 kg N ha-1 treatment.
Based on the findings of this experiment, it is recommended that an application rate of 101 kg N ha-1 or 90 lbs N ac-1 is optimal for achieving the greatest economic yield in ratoon rice cultivation in southeastern Texas.
Pest pressure:
In the ratoon crop, cultivar exerted a significant influence on weed density, with the occurrence of Narrow Brown Leaf Spot (NBLS) and Brown Spot (BS) being further impacted by rotation and cover cropping. Additionally, nitrogen (N) rates also played a role in affecting BS incidence. Notably, only N rates showed significance concerning the occurrence of white heads, as depicted in Table 3. Due to its higher tillering ability, the hybrid cultivar XP753 exhibited lower weed density compared to the inbred cultivar Presidio (Fig 7 A). This trait allows XP753 to effectively compete for space, sunlight, and resources with weeds. Furthermore, cover cropping led to an 8.6% reduction in NBLS and an 8.9% reduction in BS. XP753 also demonstrated a notable reduction in NBLS (39%) and BS (30%), as shown in Figures 7 B and C, respectively. Interestingly, the highest N rate of 135 kg ha-1 resulted in the greatest number of white heads (Fig 7 D). These findings underscore the multifaceted interactions between cultivar selection, agronomic practices such as cover cropping and rotation, and nutrient management in influencing weed dynamics and pest incidence in ratoon rice cultivation.
Table 3: Results of analysis of variance (ANOVA) for pest incidence in ratoon crop
|
Source |
DF |
Probabilities |
|||
|
|
|
Weed density |
Narrow Brown Leaf Spot |
Brown Spot |
Number of White heads |
|
Rotation (R) |
1 |
0.6363 |
0.0107 |
0.0092 |
0.1078 |
|
Cultivar (C) |
1 |
0.0002 |
<0.0001 |
<0.0001 |
0.1233 |
|
Nitrogen rate (N) |
4 |
0.9374 |
0.0884 |
0.0408 |
<0.0001 |
|
R*C |
1 |
0.7886 |
0.1611 |
0.3732 |
0.3887 |
|
R*N |
4 |
0.7497 |
0.8607 |
0.3854 |
0.3168 |
|
C*N |
4 |
0.8910 |
0.4392 |
0.5695 |
0.0253 |
|
R*C*N |
4 |
0.9590 |
0.0943 |
0.3789 |
0.6555 |
Education
This project has received additional funding from the SSARE James Harrison Hill, Sr. Young Scholar Enhancement Grant Program (YES) for the year 2023. This funding has been allocated to support the educational component of the project, which aims to investigate the effects of cover crop, genotype, and nitrogen fertilizer on ratoon rice yield in organic rice cultivation. With this funding, we have been able to train two student assistants in organic ratoon rice production systems, providing them with both specific knowledge on this topic and a broader understanding of sustainable agriculture practices in general.
As a result of their training, the student assistants have contributed significantly to the project. A PowerPoint presentation showcasing their work has been previously submitted to Southern SARE. Additionally, the student assistants will be presenting their findings at the 2024 International Temperate Rice Conference, scheduled to take place from June 5th to 8th, 2024, in New Orleans, LA.
This educational initiative not only enhances the research outcomes of the project but also fosters the development of the next generation of professionals in sustainable agriculture.
Educational & Outreach Activities
Participation Summary:
Not available at the time of preparing this report.
Learning Outcomes
Critical for Winter Cover Crop Establishment: Successful cover crop establishment is pivotal for effective weed management during the subsequent rice growing season. Excessive weed presence not only hinders cover crop growth but also interferes with rice production.
Benefits of Cover Crop on Rice Yield and Quality: Implementing a cover crop can offer numerous advantages to rice cultivation. It has the potential to enhance rice yield and improve grain quality by providing additional organic matter to the soil, increasing nutrient availability, and improving soil structure. Additionally, cover crops can help suppress weed growth and reduce the incidence of diseases, further contributing to overall crop health and productivity.
Optimal N Application Rate for Ratoon Rice Yield: Based on the findings of the present research conducted in southeastern Texas, it is being suggested that applying a rate of 90 lbs/ac N through Nature Safe (R) fertilizer could be optimal for achieving the greatest economic yield in ratoon rice cultivation. This carefully calibrated N application rate ensures adequate nutrient supply for crop growth while minimizing environmental impacts and production costs.
Project Outcomes
This project has been approved to receive additional funding from the SSARE James Harrison Hill, Sr. Young Scholar Enhancement Grant Program (YES) for the year 2023.