WHAT HAPPENS WHEN WE PLOUGH A DIRECT DRILLED FIELD? Using the soil health scorecard to monitor changes in soil health. Dr Jenny Bussell from The Allerton Project at GWCT shares the findings from research aiming to answer this question over the last three years. Growing food and fibre crops requires soils to be maintained in a suitable state that provides optimal soil structure, water retention and nutrient availability. The physical, chemical and biological properties of soil interact to deliver these functions. Measuring soil health therefore requires an integrated approach that combines the assessment of all three of these factors. There is a good understanding of the soil chemical and physical constraints to crop and grassland productivity, however, the role of soil biology is less clear. A key aim of the AHDBBBRO funded Soil Biology and Health Partnership is to improve our understanding of soil biology and to explore ways that farmers can measure and manage soil health. The Partnership has developed a soil health scorecard which aims to provide information on key indicators of soil chemical, physical and biological condition, to help guide soil and crop management decisions. There are many recognised benefits of minimising cultivation including changing soil organic matter dynamics, improving soil structure and increasing the soil microbial and invertebrate population along with the cost saving benefits of machinery, fuel and time. However, issues such as a high weed burden or compaction can arise leading to the decision to cultivate a previously direct drilled field. There is currently limited information for growers on how much this will impact on their overall soil health. As part of the partnership the Allerton Project has been running a field trial on their research and demonstration farm at Loddington for three years, looking at the impact on soil health of ploughing a field that has previously been a direct drilled field for seven years. The experiment started in 2017, when three strips were ploughed into the previously direct drilled field, creating three plough plots, and three direct drill plots across the field. These plots were monitored in autumn 2018 after one year of treatment, then again in autumn 2020, after three years of annual ploughing, and ten years of continuous direct drill. The Soil Health Scorecard approach brings together information about the chemical, physical and biological properties. The integrated report uses ‘traffic light’ coding to identify the properties where further investigation is needed to determine the management steps required to minimise any potential risks to crop productivity. Here we present the scorecard (Figure 1) for those soil properties where there is already an established evaluation framework (e.g. soil nutrients, visual soil evaluation of soil structure score – VESS). This framework is still under review in the
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final year of the Partnership and the agreed benchmarks will be released in the autumn. Treatment
Plough
Year (post-harvest, pre-cultivation)
Direct Drill
2018
2020
2018
2020
SOM (%)
7.1
7.1
7.2
7.9
pH
6.8
7.4
7.2
7.4
Ext P (mg/l) [index]
22 [3]
21 [3]
26 [3]
28 [3]
Ext K (mg/l) [index]
162 [2-]
137 [2-]
140 [2-]
173 [2-]
Ext Mg (mg/l) [index]
126 [3]
119 [3]
104 [3]
98 [2]
VESS score
2.0
2.9
2.0
2.2
*PMN (mg/kg)
71
54
74
95
Earthworms – total/pit
6
5
10
5
143
101
139
116
CO2 burst (mg/kg C) No action needed
Monitor
Investigate
Figure 1. Soil health scorecard for the ploughed and direct drilled treatments in 2018 (one year of plough; eight years of direct drill) and 2020 (three years of plough; ten years of direct drill). Numbers in square brackets indicate soil nutrient index.
Earthworms are often called indicator species due to their prevalence and visibility in the soil; they are easy to find and count and can be the first to respond to changes in the soil, such as cultivation disturbance. Earthworms are also important for soil health due to the role they play in the breakdown and mixing of soil organic matter, and the improvements they can make to soil structure and water infiltration by moving through the soil and the formation of burrows. However, earthworm numbers are seasonally variable and so should be combined with other measures to assess soil health. In 2020 earthworm numbers were low across all plots probably due to the drier soil conditions at the time of sampling and no differences were seen between the treatments. In the first year (2018) we found smaller numbers of earthworms in the ploughed plots. This was mostly due to a decline in topsoil dwelling (20 cms) earthworms, which are most at risk from direct plough damage. Topsoil structure (25cm depth) was monitored using Visual Evaluation of Soil Structure (VESS) (Figure 2). The soil at this site is a clay loam and is naturally increasingly compact at depth, however it is also vulnerable to cultivation damage where timeliness of cultivation is compromised. After three consecutive years of ploughing, we found a higher VESS score (poorer structure). In the direct drilled
ISSUE 14 | JULY 2021
