Arianna Bozzolo1, Jacob Pecenka1, Amar Patel2, Andrew Smith3

1Rodale Institute California Organic Center, Camarillo, CA, 93010
2Ravi and Naina Patel Foundation, Bakersfield, CA, 93309
3Rodale Institute, Kutztown, PA, 19530

Introduction

In modern agricultural practices, the utilization of cover crops has emerged as a sustainable solution to address various challenges, including soil erosion, nutrient depletion, and weed management. Among the diverse range of cover crop management systems, cover-crop based no-till using a roller crimper has garnered significant attention for its effectiveness in reducing tillage in vegetable production while enhancing soil health and weed suppression [1].

The roller crimper system involves terminating cover crops by rolling a large drum fitted with dull blades over the vegetation, flattening and crimping it to create a dense vegetative mat (Fig. 1). This technique not only terminates cover crops efficiently but also leaves behind a mulch layer that acts as a protective barrier, conserving soil moisture, moderating soil temperature, and suppressing weed growth. Moreover, the residue left on the soil surface serves as a valuable organic matter source, contributing to soil fertility and structure improvement over time [2].

Fig. 1: Roller crimper in action on oat and peas cover crop.

In the context of irrigated vegetable production systems along the southern coast of California, where sustainable farming practices are predominant, the roller crimper system holds particular promise. By facilitating no-till practices, this system minimizes soil disturbance, thereby preserving soil structure, reducing erosion risk, and conserving soil organic matter. Additionally, the suppression of weed growth through the roller crimper method can significantly alleviate the need for synthetic herbicides, promoting environmentally friendly weed management strategies [3].

This study aims to evaluate the efficacy of the roller crimper system in conjunction with different cover crop species and management practices for weed management in irrigated vegetable production systems. Specifically, we investigate the impact of cover crop biomass production, residue persistence, and weed suppression following termination using the roller crimper method. Furthermore, we assess the subsequent effects on crop yield.

Understanding the advantages of the roller crimper system for no-till vegetable production, in conjunction with cover crops, is crucial for promoting sustainable agricultural practices in the region. By elucidating the benefits of this innovative approach, we aim to provide valuable insights that can inform and empower farmers and agricultural practitioners to adopt more environmentally friendly and economically viable weed management strategies, thereby enhancing the resilience and sustainability of vegetable production systems along the southern coast of California.

Overview of the Study

The experiment was conducted on 20 randomized plots 46 x 12 m located at the Rodale Institute California Organic Center (34.220453, -199.108214) in Camarillo, CA. Plots were assigned to five treatments: 1) a control with no cover crop and standard tillage with a disk (Till), one of two cover crop mixes: 2) oat (Avena sativa) + hairy vetch (Vicia villosa), or 3) oat + pea (Pisum sativum), and two cover crop termination treatments, 4) conventional tillage using a disk (Till), or 5) using a roller crimper for the no-till system (No-Till). Plots with each combination of cover crop and termination method were repeated four times.

The entire field was prepared with cultivation to standardize field conditions. In March, cover crops were planted with a 4.6-m-wide grain drill (Model 1500, Great Plains Mfg., Salinas, KS) with 15-cm row spacing at seeding rate of 100 kg/ha for oat, 135 kg/ha for pea, and 22 kg/ha for vetch.  Sprinkler irrigation was used as necessary to stimulate germination (0.6 mm).

Cover crops were terminated in June, 90 days after seeding (DAS) when approx. 50% of the cover crop had reached the flowering stage to avoid the re-seeding of the cover crop. No-till plots were passed twice with the roller crimper while the tillage and control plots were passed twice with disk to partially bury cover crops and weeds growing at the soil surface.

Pumpkins (var. Howden) were direct seeded by hand in July. Pumpkins’ seeds were placed 0.9 m between rows and every 60 cm and thinned to 1.5 m after plant emergence.  After planting one line of drip irrigation tubing (T-Systems, San Diego, Calif.) was positioned on each row, drip irrigation tubing and all plants were irrigated as needed, with all the plots receiving equal amount of water.

Data Collection and Analysis

We assessed cover crop growth and weed presence at three specific time points: early June, at 90 days DAS, immediately before terminating the cover crop; late July, after terminating the cover crop (30 days after termination, DAT); and in October during harvest (120 DAT). At each sampling date, two samples were collected from each plot to evaluate both weeds and cover crops on the soil surface. Each sample consisted of a 0.25 m2 quadrat randomly placed within the field, containing all plant material within its boundaries. This plant material was then harvested, identified, weighed fresh, and subsequently dried until reaching a stable weight for final plant biomass measurement. During harvest, a subset of each plot measuring 44.6 m2 was sampled to count and weigh all pumpkins, thereby assessing crop yield.
Data were analyzed using factorial analysis of variance (ANOVA), using CoStat software (CoHort software, Monterey, CA, USA).

Results

Above ground cover crop dry biomass before termination did not statistically differ between the two cover crop mixes: 14.7 t/ha in oat/vetch and 11.3 t/ha for oat/pea. There was significantly greater weed biomass in the bare soil plots with 8.6 t/ha compared to oat/vetch with 0.3 t/ha and oat/pea with 0.8 t/ha (Fig. 2a and 2b)

Fig. 2a and 2b. Aboveground cover crop and weeds dry biomass before cover crop termination. Columns indicate Standard Error of Mean (±SEM) of a) cover crop, or weed b) dry weight biomass before termination with a roller-crimper or disk. Tukey’s HSD test was conducted to compare the means with a significance level of α = 0.05. Different letters in the column indicate significant differences between groups. n.s. not significantly different.

Thirty days after the cover crop termination with either the roller crimper (No Till) or the disk (Till), dry cover crop biomass was present in both soil management treatments.  Previous research found that about 40 to 70% of the residue generally remains on the surface after a single disking of corn, grain sorghum or wheat residue [3]. In this study, the residue that remained on the soil after two passes of the disk was 23% for oat/vetch and 30% for oat/peas. Oat/Vetch Till plots had an average of 3.5 t/ha dry biomass, and No-Till 7.4 t/ha. Oat/pea Till had 3.4 t/ha of residues left on the soil surface, while the No-Till had 6.6. t/ha. There were no statistical differences of the tonnage of cover crops residues between oat/pea and oat/vetch, but there were differences between management.  As expected, the No-Till plots had significantly greater biomass left on the soil surface compared to the Till plots. During this sampling period, weed biomass was highly variable between plots and therefore the average weed pressure did not statistically differ among all the treatments (Fig. 3a and 3b).

Fig. 3a and 3b. Aboveground cover crop and weeds dry biomass after cover crop termination. Columns indicate Standard Error of Mean (±SEM) of a) cover crop, or weed b) dry weight biomass after termination with a roller-crimper or disk. Tukey’s HSD test was conducted to compare the means with a significance level of α = 0.05. Different letters in the column indicate significant differences between groups. n.s. not significantly different.

The final assessment of cover crops and weeds was taken 120 days after cover crop termination, at pumpkin’s harvest. The oat/vetch No-Till treatment had 6 t/ha of biomass on the soil surface, and the Till plots had 3.3 t/ha. The oat/peas No-Till had 4.7 t/ha and the oat/peas while the Till treatment had 1.3 t/ha of cover crop biomass remaining on the soil surface. Weeds were present in all the treatments but with different pressure. The bare soil had a significantly greater weed biomass corresponding to 3.6 t/ha, no statistical differences were found between cover crop species or soil management (Fig. 4a and 4b).

Fig. 4a and 4b. Aboveground cover crop and weeds dry biomass at pumpkins harvest. Columns indicate Standard Error of Mean (±SEM) of a) cover crop, or weed b) dry weight biomass after termination with a roller-crimper or disk. Tukey’s HSD test was conducted to compare the means with a significance level of α = 0.05. Different letters in the column indicate significant differences between groups. n.s. not significantly different.

At harvest, oat/vetch mixture, both Till and No-Till plots, had the greatest number of fruits compared to oat/pea Till. Production per hectare was similar between oat/vetch Till, No-Till and the bare soil, greater than oat/pea Till. Oat/pea Till decreased fruit weight compared to bare soil (Tab. 1). In this experiment, a lower yield across all the plots compared to the California average yield per hectare was found [4]. Cucurbit crops are highly dependent on active pollination by bees. Fruit size and seed set of cucurbits are strongly related to bee activity.  Several factors play a significant role in managing bees for effective pollination. Among these, weather is one of the most important. Environmental and disease factors can significantly influence flowering, pollination and fruit set. Rain, strong winds and high or low temperature extremes also will reduce bee activity and consequently reduce yields [5]. The low yield observed across all plots of cucurbits during the study period has been attributed primarily to an anomaly in weather conditions, particularly an unexpected rainfall event in August, coinciding with the flowering stage. This unusual rain, amounting to 69 mm, disrupted the pollination process, leading to diminished fruit set and ultimately reduced crop yields. Despite these environmental conditions that affected fruit set, this study demonstrated that the use of a cover crop mix, especially the oat/vetch mix, in combination with organic no-till using a roller crimper to terminate cover crops, can result in yields comparable to the standard tilled treatment. This study did not report soil data, but we expect the combination of a cover crop and reduced tillage will lead to improved soil health over time.

Tab.1.Number of fruits per hectare and yield per hectare of pumpkin grown on different mulching systems. Tukey’s HSD test was conducted to compare the means with a significance level (LSD) of α = 0.05. Different letters in the column indicate significant differences between groups. Significance codes: “***” = p≤0.01, “**” =p≤0.05, “*” = p≤0.1, “n.s.”= not significant.

Summary

This study provides valuable insights into the effects of cover crops on weed management in irrigated vegetable production systems along the southern coast of California. Below are the primary findings of the study:

Cover Crop Biomass and Weed Control: 

Before Cover Crop Termination (90 DAS):

  • There were no significant differences in the total dry matter of cover crop biomass between oat/peas and oat/vetch mixes.
  • Oat/vetch and Oat/peas had lower weeds biomass compared to bare soil.

After Termination (30 DAT):

  • Oat/peas and Oat/vetch No-till plots had similar residue biomass.
  • Oat/peas and Oat/vetch Till plots had similar residue biomass.
  • Weed emergence was similar in all plots.

At Harvest (120 DAT):

  • Oat/vetch and Oat/peas in NT plots exhibited greater biomass compared to T plots. Biomass reductions were observed in all plots, with oat/peas T plots experiencing the most significant decrease (61.5%).
  • Bare soil had greater weeds biomass compared to the cover crop treatments (T and NT)

Yield:

  • Oat/vetch mixture plots (T and NT) and bare soil had similar production per hectare, outperforming oat/pea T plots in terms of fruit number and production per hectare.
  • Oat/pea T plots had decreased fruit weight compared to bare soil.

Overall, these findings emphasize the importance of cover crops in weed management. Further research is needed to explore the interactions between soil management practices, plant species selection, and crop productivity in vegetable production systems. Understanding the interactions between cover crop species, management practices, and weed management is essential for developing sustainable agricultural practices that enhance productivity while minimizing reliance on synthetic herbicides and promoting environmental stewardship. By elucidating these relationships, we can inform farmers and agricultural practitioners about effective weed management strategies that integrate cover crops into vegetable production systems, thereby promoting long-term sustainability and resilience in agriculture.