Previous work has shown a link between row spacing and yield in cereals
Analysis of ADAS’s Cereal YEN database has shown some correlation between narrower row spacing and higher yield in cereals. This link is supported by previous trials which have shown a yield benefit of cross drilling (half seed rate drilled in one direction, then half seed rate drilled at 90 degrees to give a more even distribution of plants) over conventional drilling.
Precision planting results in more evenly spaced wheat plants, which should reduce competition between plants, improve light capture, and perhaps reduce disease pressure. If this is successful, there is potential for seed planting robots to be developed, which would increase yield and the efficiency of crop production, without negative environmental impacts.
Trial design and assessments
The current 2022/23 trial includes four treatments, replicated four times in randomised blocks. Each plot is at least 2.5m wide x 5m long.
- Wide rows (25cm), 325 seeds/m2
- Narrow rows (12.5cm), 325 seeds/m2
- Cross drilling (12.5cm rows at right angles), total 325 seeds/m2
- Precision planting in a hexagonal pattern, 200 seeds/m2
NIAB will assess above ground crop performance, measures of canopy development and light interception, disease prevalence, and root biomass, at appropriate intervals throughout the growing season to determine the impact of experimental treatments on crop performance. Drone flights will be used to assess spectral reflectance and collect good quality images of plant spacing. Plot yields will be measured by Oxford Agricultural Trials.
A grab sample (100 tillers) from each plot will be submitted to Cereal YEN for analysis. This will include measurement and calculation of yield components, measures of grain quality, and benchmarking of the data against the YEN dataset and recognised benchmarks and critical values.
Results: a yield benefit from precision planting
Assessments in spring and summer of canopy coverage and NDVI (Normalised Difference Vegetation Index, a spectral reflectance index indicating canopy size and greenness) showed a trend for lowest values in the wide rows and highest in the precision-planted treatment. This indicates that the precision-planted crop fully compensated for its lower seedrate, whereas the wide row treatment was slower to achieve full canopy closure.
Suggestions within the industry that wide rows reduce disease pressure by limiting spread between rows were not supported by crop assessments, which showed no significant differences between treatment in Septoria severity, but there was a trend for disease to be lowest in the precision-planted plots. It was not possible to assess the effects of planting pattern on weed numbers, as there were no weeds in the trial area.
Precision planting delivered a yield benefit of 0.95 t/ha over the average of the three drilled treatments, which were not significantly different from each other. This yield benefit resulted from an increased number of grains per ear, rather than any increase in ear numbers at harvest or grain size.
A precision-planted future?
At present, precision drills are unavailable for wheat, but are in commercial use for crops with larger seeds and lower seedrates such as maize, beans and sunflowers, so this technology could be expanded into cereal crops in the future. Robotic seeding is also in development, although at an earlier stage.
In the short-term, these and earlier results suggest that in choosing a drill, the impact of row width on yield should be a consideration, along with factors such as cultivation system, cost, etc. Although yield in this trial was not significantly different between the wide and narrow rows, there were indications that row spacing affected canopy structure and light capture. Most likely, wide rows will have a negative yield impact where crops are principally light limited, but will make less difference in situations of water or nutrient limitation.
In the longer term, the machinery industry should continue to invest in the development of precision planting for cereals.
