Yield gap analysis in oil palm production systems in Ghana

Abstract
Palm oil is the world’s most important edible oil crop, and in the Ghanaian economy, oil palm (Eleais guineensis) is the next most important perennial crop after cocoa. Since the early 2000s, the area under oil palm in Ghana expanded but average fruit bunch (FB) yields remained low at ~7 t ha-1 yr-1 in 2014, resulting in large yield gaps. Despite the pressing need to increase palm oil production and improve yields, knowledge of the underlying causes of poor yields in Ghana is lacking. The objective of this thesis was to analyse the factors that currently limit oil palm production on plantations and smallholder farms in Ghana and to assess opportunities to increase yields with improved agronomic practices. Using land suitability evaluation methods and yield gap analysis, a framework for yield intensification with ‘Best Management Practices’ (BMP) on existing mature oil palm plantings was developed. Data was acquired from online databases, farm surveys, a three-year trial established on three plantations and twenty smallholder farms across Ghana, and an irrigation and fertilizer experiment established on a large-scale oil palm plantation in Western region, Ghana. The results showed that the oil palm industry in Ghana is limited to expand large-scale plantations due to the lack of suitable and available large and contiguous tracts of lands. A feasible strategy for oil palm expansion can be sought through smallholder production, which can make use of smaller parcels of land. However, yield gaps in oil palm production were large and ubiquitous in Ghana. Using a boundary line analysis, the water-limited yield (Yw) over a planting cycle was estimated at 21 t ha-1 yr-1 FB, with yield gaps of 15.4 t ha-1 yr-1 FB at smallholder farms and 9.8 t ha-1 yr-1 FB at plantations. Poor management practices, including incomplete crop recovery (i.e. harvesting all suitable crop) and inadequate agronomic management were the main factors contributing to these yield gaps. Productivity losses were exacerbated by low oil extraction rates (OER) by small-scale processors of 12%, compared with 21% by large-scale processors, resulting in respective crude palm (CPO) oil losses exceeding 5 and 3 t ha-1 yr-1 in the crop plateau yield phase. Reducing yield gaps with appropriate BMPs can therefore make a significant contribution to closing the supply gap for palm oil in Ghana. The implementation of BMPs at plantations and smallholders was evaluated amongst those that increased yield in the short-term term (≤ 1 year) with ‘yield taking’ (improved crop recovery), and in the long-term (>1 year) with ‘yield making’ (better agronomy) practices. Compared with current management practices, average yields and yield gains with BMP were larger, and averaged 17.9 t ha-1 at plantations and 17.6 t ha-1 at smallholders. About 2.1 t ha-1 (+19%) and 4.7 t ha-1 (+89%) of the yield increase was attributed to yield taking and 4.7 t ha-1 (+36%) and 7.6 t ha-1 (+76%) with yield making at plantations and smallholders respectively. Important crop recovery activities included more frequent harvesting events and improved field access (roads, paths, weeded circles) to increase harvester efficiency and productivity, whilst analysis of fertilizer usage and leaf nutrient concentrations suggest a more balanced approach to nutrient management could contribute considerably to yield making, particularly at smallholder farms. The irrigation × fertilizer trial demonstrated the potential to obtain even larger yields with adequate water and nutrient management. Average yields of 32.6 t ha-1 FB were achieved with irrigation and fertilizer, which was 4.7 t ha-1 greater than the control (27.9 t ha-1 ) and 4.1 t ha-1 greater than with irrigation alone (28.5 t ha-1 ). Fertilizer was therefore essential for a maximum response to irrigation. The results of this thesis demonstrate the potential to increase production in Ghana by improving current management practices with BMPs. Particularly, large increases in production can be sought by improving management practices at smallholder farms which consist of the majority of growers in Ghana, but require viable integration into the oil palm supply chain to be successful. Increasing average attainable yields to 21.0 t ha-1 FB has the potential to increase national FB production almost three-fold from 2.5 Mt to 6.9 Mt (1.4 Mt CPO at 21% OER, worth about 1 billion US$ at US$750 t -1 CPO-1 ) and reduce oil palm expansion with almost 600,000 ha of land. Yield intensification can be achieved without the typical capital expenditure required for new plantings (e.g. road infrastructure, planting cost), and financial returns from investments in yield intensification accrue vi more rapidly because production starts to increase as soon as agronomic constraints are removed. Rehabilitation of existing mature oil palm plantings may therefore be an important policy for sustainable oil palm development in Ghana and West Africa.