- Author: Michelle Leinfelder-Miles
- Author: Brenna Aegerter
In 2020, we completed a three-year on-farm trial in the Delta to evaluate warm-season legume cover cropping between winter small grain forage crops. Cover cropping is a management practice identified in the Healthy Soils Program of the California Department of Food and Agriculture as having the potential to improve soil health, sequester carbon, and reduce greenhouse gas emissions. Our objectives were to evaluate summer cover cropping for its potential to improve soil tilth at a time of year when the soil would usually be fallowed and dry with no soil cover, and to better understand the agronomic practices that might make summer cover cropping more feasible for Delta farmers. This article summarizes select results from the trial. A detailed report is available on the Delta Crops website.
The trial took place over 4.5 acres of a commercial field, and we compared a cowpea (cultivar ‘Red Ripper') cover crop treatment (CC) to fallow soil (No CC). The cultural practices varied across years (Table 1). Irrigation was only applied to the cover crop plots. In 2020, we estimated that five inches of irrigation was applied to the cover crop, using surface water with moderately low salinity (seasonal ECw of 0.5 dS/m).
Table 1. Agronomic practices during the three-year study.
We soil sampled twice per year. The first sampling occurred following triticale harvest but prior to tillage and cover crop planting. The second occurred at the end of the cover crop season immediately prior to cover crop termination. Soil was sampled from 0-6, 6-12, 12-24, and 24-36 inch depths. We evaluated bulk density, salinity (electrical conductivity, ECe), pH, total nitrogen (N), and total carbon (C). Additionally, in-situ water infiltration was measured at the conclusion of the project (i.e. prior to 2020 cover crop termination). We hand-harvested cover crop biomass, separated it into cultivated cowpeas, volunteer small grains, and weeds and analyzed each component for total C and N. We hand-harvested triticale forage in 2019 and 2020.
Soil properties. After three years of cover cropping, we did not observe improvements in total N or bulk density from cover cropping, and our statistical analysis indicated that total C was impacted by plot location. This suggests that an inherent soil characteristic, like texture, was having more of an impact on total C than the cover crop treatment. We observed better water infiltration in the CC plots (Figure 1). Cover crop roots likely contributed to better soil structure and water conductance. We also observed lower salinity and higher (i.e. less acidic) pH in the CC plots. Root zone salinity (0-36 in) averaged 1.4 dS/m in the CC plots and 2.2 dS/m in the No CC plots. Root zone pH averaged 5.7 in the CC plots and 5.5 in the No CC plots. These results suggest that cover cropping can improve certain soil characteristics, particularly those related to soil-water status, on a relatively short time frame. Changes in nutrients and C storage, however, are less likely to be observed following short-term changes in management.
Figure 1. Three years of cover cropping improved water infiltration (P=0.0198) compared to the standard dry fallow. The error bars represent the standard errors. The photo illustrates how there were visible differences between treatments, even after triticale forage harvest and uniform tillage operations. No CC soil was a fine powder (bottom of the photo); whereas, CC soil was observed to have better aggregation. The grower observed differences in subsequently-planted small grains, with seedlings in the CC plots emerging about five days earlier than seedlings in the No CC plots.
Cover crop stand. Cover crop composition varied over the course of the study and was likely impacted by cultural practices, like planting and irrigation methods. While cowpea was the only seed planted, the stand was a mix of cowpea, volunteer wheat/triticale, and weeds. We observed that the 2020 practices and timing of operations resulted in the least amount of weed growth (Figure 2) and seed heading.
Figure 2. Proportion of cowpeas, small grains, and weeds in total cover crop biomass, and total C and N inputs from the cover crop.
Triticale forage yield. Despite certain soil health benefits, cover cropping did not improve triticale forage yield. The No CC treatment yielded higher than the CC treatment across both years (Figure 3). The CC plots yielded below the two-year field average of 5.5 tons per acre, and the No CC treatment yielded above the field average yield. Given the improved infiltration, pH, and salinity conditions in the CC treatment, the yield result is difficult to explain, but machine harvesting over a larger area might lessen the difference between treatments.
Figure 3. Triticale forage yield as tons of dry matter per acre. The No CC treatments yielded higher than the CC treatments across both years (2019-2020) (P=0.0059).
Summary. In our three-year study, cover cropping had no effect on total N, bulk density, and total C, but water infiltration, salinity, and pH were improved. Triticale forage (i.e. cash crop) yield did not improve as a result of cover cropping, however. Cowpea stand establishment and volunteer grain and weed competition were the biggest challenges to growing a summer cover crop at this site, but earlier planting and termination reduced the weed pressure. Despite these challenges, the grower observed better soil aggregation in areas of the field where the cover crop had grown. Overall, the potential benefits of cover-cropping may not be realized in the first few cover crop cycles, which could hinder long-term adoption. Results may also depend on the cover crop biomass obtained and other site-specific factors. While scientific studies have demonstrated soil health and cash crop yield improvements with cover cropping, more long-term studies are needed in California to demonstrate how these benefits can be realized.
Acknowledgments. This project was supported by the California Climate Investments program. We thank Dawit Zeleke, Morgan Johnson, and Jerred Dixon of Conservation Farms and Ranches for hosting the trial. We thank Tom Johnson of Kamprath Seed and Margaret Smither-Kopperl and Valerie Bullard of the NRCS PMC for information and advice on cover cropping.
Weeds are important pests of California rice systems, and weed management can account for roughly 17 percent of total operating costs (Espino et al., 2016). Integrated weed management uses cultural and chemical practices where herbicide are important tools. Certain conditions in California rice production systems, however, increase the likelihood of developing herbicide resistance. Herbicide resistance is the ability of certain weed biotypes to survive certain herbicide treatments when the weed species is usually killed by that herbicide (Al-Khatib et al., 2019). Such conditions include, but are not limited to, lack of crop rotation, the efficacy of certain herbicides on certain weeds causing them to get frequently used, and not having diverse chemistries available.
In 2019 and 2020, trials were conducted to evaluate the efficacy of a new herbicide product called Loyant (florpyrauxifen-benzyl; group 4 herbicide; Corteva Agriscience) in drill-seeded rice in the Delta region. Loyant is registered in rice growing states in the southern US but would be a new chemistry in California. Corteva Agriscience expects to have CA registration in time for the 2021 use season. The objective of the trials, by assessing different rates and treatment combinations, was to understand the efficacy and crop tolerance of Loyant for weed control in drill-seeded rice in California. This article will describe select results of the 2020 trial. Treatments are listed in Table 1 below. Complete information from both years is available from my website.
Crop injury. We made crop injury observations and weed counts on 7-day intervals for about two months following treatment. We observed tip burning in several of the treatments, but the symptoms were no longer apparent by 21 days after treatment (DAT). We observed leaf curling in the Loyant treatments until about 56 DAT. Corteva Agriscience has observed this symptom with Loyant in other trials where environmental stressors impact crop health, such as extreme cold or heat, drought, or poor fertility. We observed this symptom on the side of the plots closest to the field edge. We observed no stunting, stand reduction, or differences in heading with any treatments.
Weed control. Overall weed pressure was relatively low, observing about 1 weed per square foot in an untreated strip next to the trial. The prominent weeds in the field were Echinochloa species (i.e. watergrass, barnyardgrass; Figure 1, below). We did not have a completely untreated control but instead considered the pre-emergent only treatment (i.e. Prowl) the control. There was a trend for the Prowl treatment to have the highest weed counts. The treatments that had the best weed control were the grower standard and Loyant/SuperWham herbicide programs (Table 2, below).
Yield. We found no differences in yield, but there was a trend for the grower standard and the Loyant/SuperWham herbicide programs to have slightly higher yields (Table 3, below). Measured yields were uncharacteristically high for the region. Our explanation of the data is that we did our hand harvest in the early morning hours when there was a heavy dew. Because variability across the replicates was low, as indicated by the coefficient of variation, we believe the data demonstrate relative comparability of herbicide programs, even though the absolute values are high.
Conclusions. The purpose of the trial was to learn the efficacy and crop tolerance of Loyant (florpyrauxifen-benzyl) for weed control in California drill-seeded rice. We observed Loyant to have good activity on watergrass and barnyardgrass, which were the predominant weeds in the trial. We observed Loyant treatments to have similarly low weed counts compared to the grower standard, and a Loyant/SuperWham herbicide program appears to provide comparable weed control to the grower standard. The results demonstrate that Loyant could be used in drill-seeded rice herbicide programs, providing a different chemistry for herbicide resistance management.
The aforementioned information on products and practices is for educational purposes only and does not constitute an endorsement or recommendation by the University of California.
Table 1. Herbicide treatments in the 2020 trial. Treatments were applied on May 8th, when the rice was approximately at the 3rd leaf stage.
Figure 1. Predominant weeds in the trial were watergrass and barnyardgrass.
Table 2. Weed counts on 7-day intervals from 14 DAT to 42 DAT. Data represent total number of weeds in the 400-ft2 plot and are the means across four replicates.
Table 3. Yield adjusted to 14 percent moisture. The trial was hand-harvested on Sept. 29, measuring one 10.8-ft2 (1-m2) quadrat per plot. The grower reported that harvest moisture was around 18.5 percent.
Happy New Year! Here are two opportunities for virtual continuing education.
1. The California Plant and Soil Conference will be held virtually February 1-3, 2021, and registration is now open. Please see the website for more information and to register. The conference includes sessions on:
- Covid-19 Impacts on Agriculture
- Automation in Agriculture
- Remote Sensing
- Irrigation Optimization
- Nutrient Management
- Cover Cropping
- Evaluation of Biological Inputs
- Practical Indicators of Soil Health
- Pest Management
We have applied for DPR pesticide licensing credits (Other: 2.75), CCA credits (Total 12.75; Categories: Nutrient Management: 3.5, Soil & Water Management: 3.0, Integrated Pest Management: 2.0, Crop Management: 3.5, Professional Development: 0.75), and Nitrogen Management credits (5) to help growers fulfill their Irrigated Lands Regulatory Program requirement. These credits have not yet been approved and are subject to change.
2. The UCCE Rice Grower Meeting will also be held virtually on February 11, 2021 from 9am to noon. Registration is now open, and a full agenda is available from the registration page. There will be presentations on the following topics:
- Ag Commissioner Update
- Weed Management
- Disease Management
- Arthropod Management
- Bird and Salmon Projects Update
- Emerging Weed Issues
- Fertility Update
- Roxy Rice and Variety Update
We have applied for DPR pesticide licensing credits (Other: 1.25, L&R: 0.5) and CCA credits (Total: 2.5; Categories: Pest Management: 1.5, Crop Management: 1.0). These credits have not yet been approved and are subject to change.
Please don't hesitate to reach out with questions on either of these events, and we hope to see you there!
As the Covid-19 pandemic persists, and as government mandates and University recommendations maintain that we should social distance, I have come to the conclusion NOT to hold the annual SJC and Delta Field Crops Meeting in January. Instead, I am working with colleagues to deliver virtual continuing education early in the new year:
The California Plant and Soil Conference will be held virtually February 1-3, 2021, and registration is now open. Please see the website for more information and to register. We have applied for DPR pesticide licensing credits (2.75), CCA credits (12.75), and Nitrogen Management credits (5) to help growers fulfill their Irrigated Lands Regulatory Program requirement. These credits have not yet been approved and are subject to change.
The UCCE Rice Grower Meeting will also be held virtually on February 11, 2021. This meeting is still being developed, and I will post more information once registration is open. In the meantime, please save the date!
Please don't hesitate to reach out to me if you have questions regarding these events. I hope that the pandemic has not severely impacted you or those close to you, and I wish you safe, healthy, and happy holidays.
UC Cooperative Extension will offer a virtual Alfalfa IPM Workshop on December 3rd and 4th. The workshop will run from 9am to 12pm on each day. Registration is required, and there is a $25 fee to help cover our costs of delivering a workshop virtually. Continuing education credits will be offered. (5 "Other" credits from DPR and 4 "IPM" credits for CCAs.)
Day 1. December 3 (9 am - Noon PST) Weed and Pest Management Strategies
- Price & Acreage Trends -- Josh Callan, The Hoyt Report, Twin Falls, ID
- California Regulatory Update--Dennis Albiani, Ag. Management, Sacramento, CA
- Key Agronomic Strategies for Pest Management--Dan Putnam, UC Davis
- Poisonous Weeds of Concern in Alfalfa--Larry Forero, UCCE, Redding, CA
- Weed Control Strategies for Establishment and Production -- Earl Creech, Utah State University, Logan, UT
- Recent Weed Control Trials in Alfalfa--Tom Getts & Giuliano Galdi, UCCE, Susanville and Yreka, CA
- Weed Mangement Strategies for Pastures--Josh Davy, UCCE, Redding, CA
Day 2. December 4 (9 am-Noon PST) Insect, Disease Management Strategies
- Process of Pesticide Regulation in California--Aron Lindgren, DPR, Sacramento, CA
- On-Line Tools for Pest Management Information--Jose Luiz Carvalho de Souza Dias, UCCE, Merced, CA
- Management of Insecticide Resistance in Alfalfa--KEvin Wanner, Montana State Univ.
- Biological Insect Control in Alfalfa: A Case Study--Ian Grettenberger, UC Davis
- Update on Low Desert Forage Insects--Michael Rethwisch, UCCE, Blythe, CA
- Summer Worm Management--Rachael Long, UCCE, Woodland, CA
- Potential Use of Drones for Insect Management--Ken Giles, UC Davis
- Key Diseases and Management in Alfalfa--Deborah Samac, USDA-ARS, St. Paul, MN