What is a yield gap?
Yield gaps are calculated as the difference between the actual yield (Ya) and an estimate of potential yield, based on an assessment of the site-specific characteristics (e.g., soil type, planting material, age of trees).
What is potential yield (Yp)?
Potential yield (Yp) is defined as:
The yield of fruit bunches for palms planted at the optimal plant spacing for a given soil type and planting material for each year of production from the onset of harvest to the end of the production cycle where productivity is not limited by nutrient supply, pests, diseases, weeds, soil damage and other factors amenable to management control.
Where can the estate manager obtain information on potential yield?
Records from optimal treatments in properly implemented fertilizer experiments are a useful source of information but usually only provide data for a few years in the production cycle. A further source of information is seed suppliers who may have conducted trials in representative soil types to estimate the productivity of particular planting materials in different environments. As we shall see, it may also be possible to make use of past yield records and estimate Yp based on the performance of the top 90th percentile (top decile) for each year of production for each soil type and planting material. Perhaps the most appropriate approach to estimating Yp, however, is for the estate to implement BMPs in selected fields, with a full tree stand at the optimal density, that represent the dominant land classes found on the estate.
How do I use yield gap information?
Conventional approaches to plantation management usually include the implementation of programmed field maintenance and upkeep programs in each administrative unit or division within the estate together with field visits by management staff to review the quality of implementation and provide corrective advice. Yield data (t ha-1 fruit bunches, bunch weight, bunch number per palm) for individual fields and administrative units may be compared in an attempt to identify areas with low productivity. This does not necessarily provide a high return on investments in management inputs since there is no guarantee that the manager's time is spent in those areas where corrective agronomic measures are required.
An estate achieves the greatest return to the inputs of management staff when attention is focused on fields where the yield gap (Yp-Ya) is greatest. It is not an easy task to calculate yield gaps since each field of palms may differ in terms of planting date, soil type and planting material, the three factors that determine the potential yield. For example, a 6750 ha estate with six planting years, three land classes, and one planting material, there may be 18 different 'potential yields' for each year of production. In other estates with several planting materials, planting years and land classes there may be more than 30 'potential yields' for each year of production. Clearly, it is not an easy task to identify those blocks that are under-performing without the use of computerized database tools.
What tools are available to do yield gap analysis?
Central to our approach is the use of integrated decision support tools comprising OMP7™, a computer database system for the storage and analysis of agronomic data, and geographical information systems (GIS) for the spatial analysis of agronomic information. Each block is classified according to planting date, planting material and land class and yield profiles are described for each land class. Thus, the potential yield (not adjusted for variation in rainfall) is identified automatically and correctly for each field each year. The 'yield gap' is then calculated as the difference between potential and actual yields.
Conclusions
Yield gap analysis is a powerful tool to identify poorly performing blocks according to tree age, planting material and land class. Yield gap analysis requires that all agronomic information for each field and year of production is stored in a computer database together with Yp projections for each land class and planting material. It is then possible to produce maps showing poorly performing areas in the estate that merit site-specific remedial action and greater inputs from management staff. Reports can be prepared that list blocks sorted according to yield gap and provide background historical information on yield, nutritional status and maintenance standards.
Such maps and reports provide essential quantitative information that can be used to compliment the time worn procedure of field visits so that programs for remedial and corrective action can be devised focusing on areas of the estate where the return on investment in management effort as well as labour and materials is greatest.
Source
Griffiths, W. T., Fairhurst, T., Rankine, I., Gfroerer-Kerstan, A. and C., T. (2002) Identification and elimination of yield gaps using OMP7 and GIS. In: International Oil Palm Conference. Indonesian Oil Palm Research Institute (IOPRI), Bali, Indonesia,
Download full paper from the internet: yield gap analysis .pdf
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