Towards precision inputs through improved understanding of the underlying causes of in-field variation in lettuce crop maturity and yield

Boubou, Y. (2018) Towards precision inputs through improved understanding of the underlying causes of in-field variation in lettuce crop maturity and yield. Doctoral thesis, Harper Adams University.

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Abstract

In-field variability in the yield of the mature lettuce heads affects the efficiency of a single-pass harvest. Heads that do not acquire the target weight range and quality at harvest result in crop wastage. Understanding the overall causes of this variability may inform targeted solutions for improving yield uniformity. Examining the potential for using current tools in precision farming, such as soil apparent electrical conductivity (ECa) scans and geographic information systems may help identifying the effects of soil heterogeneity on this variation. This in turn will support the making of precision management decisions. The central hypothesis for this study was that there are underlying physiological and edaphic factors that control the spatial variability in lettuce fields. Five field experiments and four glasshouse experiments were conducted between 2014 and 2017. Scans of ECa identified field zones of difference in both yield and soil. Zones varied statistically in clay content, magnesium, potassium, phosphorus, as well as, plant fresh weights 35 days after planting and at harvest. However, the underlying variation in ECa did not explain this difference. Grid sampling studies showed that lettuce yield varied spatially but not seasonally, and that bulk density was the strongest predictor for lettuce yield for two successive crops. The results of field studies suggest that in-field variation in lettuce yield is mainly derived by soil type and soil physical properties such as bulk density, the mineral fraction of the soil texture, organic matter and soil profile. Glasshouse studies explored the effect of transplant dissimilarities on the variation in plant growth after transplanting. Transplant weights and sizes varied considerably within trays and this variation amplified 14 days after planting. Furthermore, variations in transplant orientations and depth at transplanting affected significantly the quality and the quantity of the final yield. Glasshouse studies suggest that a considerable proportion of the variation in lettuce yield is a result of dissimilarity in transplant sizes at the propagation stage and farming practices during transplanting ECa scans helped identifying different soil zones within the studied field and enabled targeted soil sampling which revealedsignificant variations in soil properties and lettuce yield. Variable field zones could be identified using soil EC scans, maps of soil properties, as well as the yield maps. Field areas that varied in EC ranges varied statistically in soil texture and major nutrients.And whilst lettuce yield in this study varied spatially and not temporally. It was also found that there is a proportion of the variation in lettuce yield starting at early stages of growth, before and at the transplanting in the field. Bulk density was the strongest predictor for both yields of lettuce. The suggested role for organic matter in the variability of the yield was supported by the glasshouse experiments.

Item Type: Thesis (Doctoral)
Divisions: Crop and Environment Sciences
Depositing User: Ms Kath Osborn
Date Deposited: 15 Nov 2019 10:30
Last Modified: 01 Jan 2020 05:10
URI: http://hau.repository.guildhe.ac.uk/id/eprint/17463

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