Murphy, Leona
(2021)
Optimising canopy size and structure in field beans (Vicia faba) grown in a temperate climate.
PhD thesis, University of Nottingham.
Abstract
Field beans are an up-and-coming crop in Irish agriculture, helping to reduce imports of feed protein and encouraging a home-grown source for cattle feed. Since the introduction of the protein grant in 2015 as part of the Common Agricultural Policy (CAP) greening scheme, the area of field beans sown in Ireland has increased rapidly. However, due to their unpredictable year on year variation in yield, field beans have not yet reached their full potential in Irish agriculture. A better understanding of their growth and development as well as management of the crop for full yield potential is essential to encourage growers to avail of the added benefits of having field beans in their crop rotations.
This thesis outlines research which aimed to develop a better understanding of the agronomy and physiology of field beans in the temperate Irish climate, to gather information and create advice for Irish growers on the best way to grow and manage field beans. This was achieved through three years of field experiments from 2017-2019, where different sowing dates, seed rates and varieties were used to vary the canopy size. Through this canopy manipulation, the variation in leaf green area, pods per unit area and seeds per unit area was evaluated in order to identify the key components of yield in field beans.
Throughout this research, several parameters were studied. This thesis outlines the results of this study on the effect of sowing date, seed rate and variety on the growth and development of the field bean crop in a temperate climate. The results of this study found that even though field beans show great variability in yield from year to year, with the correct sowing conditions and management, they have the potential to produce high yields in the Irish climate. Using a broad range of seed rates from 10 – 80 seeds per square metre over six sowing dates, the response of field bean yield to these factors could be thoroughly studied over three years. In 2017, yield in this study was found to be 6.2 t ha-1, which was close to the national average yield for field beans of 6.7 t ha-1 (Teagasc, 2018). Yield was found to be the lowest in 2018 when it dropped to 2.5 t ha-1 due to lower-than-average rainfall from pre-flowering to harvest.
The October sowing date generally yielded highest for the winter sown treatments and February/March for the spring sown treatments, coinciding with the current recommendations for sowing field beans in Ireland by the Department of Agriculture, Food and Marine (DAFM). However, with the variation found in crop establishment over the three years of study, yield was examined and presented against plant populations instead of seed rate. The general trend showed that as plant populations increased, yield increased. This led to the study of the economic plant population in field beans for Ireland, which we believe to be the first to report. The economic plant population for the spring variety was between 24 – 38 plants per square metre and 13 plants per square metre for the winter variety. This study concluded that yield and profit will not improve by sowing at higher plant densities.
Further study into the components of yield in field beans found a strong relationship between pod number and final yield. It was generally found that pod number closely related to the Green Area Index (GAI) of the crop during the pod development phase of growth, which led to the hypothesis that light interception during the pod development phase determined pod number and thereby yield. A supplementary experiment was carried out to support this, where shades were erected over the plots, reducing the intercepted radiation by c.60%. This found that when light was reduced during the reproductive phase, there was a 27% yield reduction, resulting from a 38% reduction in pod number. With green area strongly relating to pod number per square metre, it can be concluded that radiation intercepted during the reproductive phase is crucial for the determination of pod number which in turn is a driving factor in final yield of field beans.
Crops like cereals and oilseeds have been studied to determine management strategies for fertilisers and spray treatments throughout the season. Field beans are a relatively new, up and coming crop in Irish agriculture and the knowledge behind field bean management in Ireland is being trialled. This study found that green area in field beans is strongly related to leaf fresh biomass. From this, we hypothesised that leaf fresh biomass can be used as a predictor of GAI and in turn be used by growers as a tool in canopy and overall crop management throughout the season. A model was created using the relationship between leaf green area and leaf fresh biomass, resulting in the equation y = 0.0021x – 0.0734. Using an independent field bean data set and the equation from the model, results showed a strong correlation between measured leaf green area and predicted leaf green area with an R2 = 0.92 and RMSE of 0.38.
The greater understanding of yield components and the driver of final yield in field beans will lead to further studies in this area and a greater understanding of this potentially high yielding crop in temperate climates. Overall, the findings in this thesis are a foundation for further research in field beans and other protein crops in Irish agriculture.
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