Scope
The Soil Erosion Experiments (Commissioning Project, Cranfield Soil and Agrifood Institute, 2018) aimed to investigate and address three key soil and crop health challenges faced by the agricultural industry, namely:
- The effect of rainfall events on the rates of soil and water losses
- The effect of rainfall intensity and soil surface sealing on seedling germination, emergence, and growth
- The contamination of fresh produce (salad leaves) by rain splash soil detachment
Methodology
The soil erosion trays were prepared with spinach, clover and bare soil, and placed at two slope gradients of 3o and 10o to represent arable/horticultural field conditions. Cranfield’s rainfall simulator was calibrated to give representative storm events, with realistic rain drop sizes, velocities, and kinetic energies, confirmed using a laser optical distrometer. Rainfall was applied at three key stages of crop development: newly cultivated seedbed; shortly after emergence; and established crop.
Vegetation biomass, soil moisture, time to runoff initiation, runoff and infiltration/leachate volume, sediment concentration, sediment load and splash detachment rate were measured during and after each storm event.
After each storm event, the erosion trays were moved into CHAP growth rooms and kept at controlled temperatures, humidity and light. Although the experiments began in January, the growth rooms could simulate typical UK mid-May conditions.
Results
A positive correlation between sediment and runoff volume was observed overall for storms, slope gradients and treatments (see Figure 1). It was expected that sediment loads would be greater on the steeper slope, and this was true for all the treatments at all stages of testing. These results reflect what is expected to happen in the field, demonstrating that the facilities are representative of reality, but with control of the environmental variability that can confuse results from field studies.
Figure 1: Correlation between runoff (l) and sediment load / soil loss (g) for all experimental conditions (rainfall events, slope gradients and treatments).
After Storm 1, the bare soil yielded the highest splash detachment rates, compared with clover and spinach (see Figure 2). As the vegetation covers developed, no significant differences were seen between treatments on any slope at any stages of testing, with the exception of the steeper slope after Storm 2, where the bare soil yielded significantly more splash detachment than the spinach. By the time some vegetation cover had developed to intercept raindrops impacting the soil surface (i.e. after Storm 3), the vegetated treatments had less splash detachment than the bare soil, but this was only apparent on the steeper slope.
Figure 2: Total splash detachment (g) per storm event for each vegetation cover and slope treatment. Error bars show ± 1 SE.
Vegetative cover increased for spinach and clover over time, being higher downslope (see Figure 3), possibly due to the higher soil moisture content due to water accumulation in the lower half of the erosion tray. By Storm 2 and Storm 3, the spinach had greater coverage than the clover. After the trials, final leaf area was measured using a Leaf Area Meter.
Figure 3: Typical clover (top) and spinach (bottom) treatments (steeper slope, pre storm 3).
Leaf contamination by rain splashed soil was measured at the end of the trials. By Day 21, it was possible to measure the amount of material splashed onto the leaves, which was particularly evident in the spinach (see Figure 4). The amount of leaf contamination with splashed soil was not significantly different for the two slope angles.
Figure 4: Leaf contamination from rain-splashed soil observed on spinach treatments following storm 2.
An extensive soil surface crust was observed on all treatments. Sheer strength measurements of the surface crust showed significant increases for the bare soil treatment as compared with the spinach on both slope gradients.
Impact
The soil erosion trays can be used to simulate soil hydrological processes that affect soil and crop health, such as erosion by rain splash and runoff, overland flow, infiltration, soil surface sealing/crust formation and rain-splash contamination of leaves. The facilities enable these processes to operate at realistic spatial and temporal scales. The experimental set up can produce statistically significant results for the different treatments imposed, demonstrating that hypotheses can be tested with empirical evidence generated by use of the erosion facilities.
It was possible to observe and record differences in soil moisture, splash detachment, vegetative cover and leaf contamination between treatments, and to establish a positive correlation between runoff and soil loss. The controlled environment of the CHAP growth chambers means that the trays can be subjected to ‘out of season’ conditions, which will deliver robust and reliable research outputs for users all year round (showing an advantage over field trials).
The success of the project in answering each of the specific industry-led research questions gives confidence that the CHAP Soil Health Facility offers an extensive range and combination of experimental conditions to address future applied research questions.
The Erosion Experiments demonstrated the capability and flexibility of the Erosion Laboratory at Cranfield University in addressing key soil health challenges posed by industry. CHAP soil erosion trays are easy to prepare, including the simulation of different field operations such as cultivation and crop establishment, providing consistent and realistic starting conditions.
For more information go to our Plant Phenotyping and Soil Health Facility and Soil Health Solution pages. To see another project using this facility go to Using Roots to Bio-engineer Soil; or visit YouTube for a brief overview of the Phenotyping and Soil Health facilities.
