Soil Amelioration & Groundcover Post-Harvest: Implications for Farmers

By Kate Parker, WMG Project Officer

Introduction

The months between harvest and seeding are a critical period for maintaining soil health, protecting productivity, and enhancing environmental resilience. Groundcover during this time plays a vital role in reducing erosion, improving soil moisture retention, and sustaining long-term soil function.

As part of a 2024 trial conducted on Tim Creagh’s gravel soil paddock in Dandaragan, funded by GRDC through the Soil Water Repellence Project, WMG observed significant differences in post-harvest groundcover between ameliorated and untreated (control) plots. These findings offer practical insights into the broader benefits of soil amelioration techniques beyond their primary targets, providing valuable implications for farm management decisions.

The Role of Groundcover After Harvest

Groundcover refers to the plant residue and biomass that remains on the soil surface after harvest. It plays a key role in reducing wind and water erosion, moderating soil temperature, improving moisture retention, and minimising nutrient loss. In farming systems where summer rainfall is variable and soil structure is fragile, maintaining groundcover during the fallow period is critical.

The primary aim of the 2024 trial was to assess soil amelioration methods in relation to water repellence. However, during a mid-March soil sampling visit, distinct differences in groundcover between treatments were observed (see Image 1). Four treatments were evaluated:

• Plozza ploughing
• Nufab deep ripping (single and double pass)
• Plozza ‘Fanger’ mixing
• Control (no amelioration)

These treatments aimed to reduce soil water repellency, alleviate compaction, and enhance crop performance. Observations made post-harvest suggest that amelioration also contributed to increased groundcover, particularly where treatments disrupted weed seed banks and improved crop biomass.

Tracking Biomass and Groundcover via NDVI and Satellite Imagery

Satellite imagery—including Normalised Difference Vegetation Index (NDVI) and high-resolution colour imagery—was used throughout the 2024 season to track changes in plant health and groundcover. NDVI is a reliable indicator of photosynthetic activity and biomass, while colour imagery provides visual evidence of plant density and canopy closure.

Satellite data from 19 June, 19 July, 17 September, 17 October, 16 November, and 16 December 2024 showed clear temporal trends. Early in the season, NDVI values were higher in control plots, likely due to weed growth (notably capeweed and ryegrass), which inflated biomass measurements but competed heavily with crops. As herbicide treatments took effect and crop development progressed, NDVI in control plots declined while values in ameliorated plots increased.

By December, the contrast between treatments was clear. Colour imagery showed reduced groundcover in control plots, whereas ameliorated areas maintained dense, healthy biomass well into the post-harvest period. This suggests that ameliorated soils better supported crop growth and retained groundcover benefits into the summer.

Table 1. Satellite imagery of NDVI and colour at trial site across the 2024 season (DataFarming platform).

Weed Pressure and Biomass Development

Weed presence significantly influenced biomass patterns throughout the trial. In untreated control plots, weed burden was initially high, resulting in elevated NDVI. However, after knockdown herbicide applications, weed cover diminished and crop performance lagged behind that of ameliorated plots.

Amelioration treatments improved early-season weed control by burying weed seeds and disrupting germination. As a result, crop growth was less restricted, biomass was higher at key growth stages (e.g. GS30 and anthesis), and post-harvest groundcover was visibly stronger.

This shift in competitive dynamics—once crops became dominant—was reinforced by stronger root systems and improved water availability. The combination of fewer weeds and healthier crops contributed to sustained groundcover through to late summer.

Why This Matters for Farmers

Maintaining groundcover after harvest is vital for protecting soil health, particularly in fragile or water-repellent soils like those common in Dandaragan. Soil amelioration techniques that improve crop biomass during the season can contribute to significantly improved groundcover during the fallow period.

Improved groundcover offers several benefits:

• Reduces erosion from wind and water
• Enhances moisture retention for following crops
• Supports soil microbial activity and nutrient cycling
• Minimises the need for costly post-harvest erosion control

By improving crop establishment and reducing early-season weed pressure, amelioration treatments offer both agronomic and environmental gains. These benefits may be especially valuable in years with challenging seasonal conditions.

Future Research Opportunities

The promising results from this trial point to a need for further research into the post-harvest benefits of soil amelioration. Future studies should explore:

• Long-term effects on groundcover and erosion control
• Interactions with soil microbial communities
• Integration with weed management programs
• Variability across soil types and seasonal conditions

Understanding these dynamics will help fine-tune amelioration techniques to maximise both productivity and soil health.

Conclusion

Soil amelioration has demonstrated the potential to significantly enhance post-harvest groundcover by improving biomass production and reducing weed pressure. These outcomes provide farmers with practical tools to improve soil condition, reduce erosion risk, and better prepare paddocks for the following season. As farming systems continue to adapt to climate variability and soil constraints, integrating amelioration into broader soil and crop management strategies will be key to building resilience and long-term productivity.