Effect of slow release and potassium fertilizers on oil palm
Prof. Festo Massawe (Nottingham University, Malaysia)
Start: 2018 – End: 2020
Fertilizers account for 50-70% oil palm field operational cost and about 25% of the total cost of production. Oil palm requires high quantities of fertilizers, especially nitrogen (N) and potassium (K) to produce high oil yield. Cultivation of oil palm faces several production constraints including poor soil fertility (e.g. sandy soils) and fluctuating soil water content. In order to overcome these constraints, plantation industry use inorganic fertilizers to enhance soil fertility to support oil palm productivity.
Malaysia, one of the largest exporters for palm oil, is located near the equator with a hot and humid climate, exhibiting seasonal rainfall of up to 2500 mm annually. However, recent unpredictable weather patterns have significantly influenced the plantation operation especially fertilizer application regimes. Frequent application of fertilizers to oil palm plantation coupled with high rainfall intensity potentially increase the risk of losing nutrient from the soil through runoff or leaching out of the rhizosphere. According to Foong (1993), leaching losses measured through lysimeter study was higher in immature oil palms (17% N, 10% K and 70% Mg) aged one to four years compared to mature palm (2% N, 2.5% K and 12% Mg) aged five years and above. Limited canopy coverage and underdeveloped root systems are among the reasons for leaching losses.
Mineral fertilizers either singly or as mixture fertilizers (e.g. urea, ammonia sulfate, MOP) are widely used in oil palm plantation in Malaysia to enhance soil nutrient content for higher oil yield production. These conventional fertilizers are highly soluble in water and the timing of fertilizer application is crucial to ensure efficient and optimal uptake of fertilizers. The loss of nutrients from the soil reduces crop productivity and economic profitability, and exerts negative impacts to the water resources and greenhouse gases emissions. Several field practices are adopted to minimise nutrient loss due to leaching, including splitting application rate into a number of small doses, which indirectly increase the frequency of application and labour cost. The common plantation practice in oil palm field is to apply N and K fertilizers two to three times per year while kieserite and rock phosphate are applied once a year. Application frequency is generally higher in young palms with the use of compound and mixed fertilizers supplemented with straight fertilizers. The growing concerns of production cost and labour shortage has led to the recommendations of using controlled release fertilizers (CRF), as written in RSPO manual ‘Best Management Practices for Oil Palm Production’. As compared to conventional fertilizers, CRF with nutrient granules coated with a thin layer of a physical barrier are able to regulate the rate of nutrient release by either diffusion or osmosis when they are in contact with water and influenced by temperature. CRF potentially offers advantages of reduced leaching loss, improved nutrient use efficiency and sustainable production of oil palm.
A number of studies have investigated the roles of CRF in reducing nutrient loss from the soil in a wide range of crop species. One recent field trial, which studied runoff loss of applied nutrients in oil palm using CRF, showed a decreased risk of nutrient loss from 6.97% to 2.44% in N, 13.37% to 5.09% in K and 14.76% to 5.43% Mg (Bah et al., 2014). In addition, a recent trial at the University of Nottingham, UK that studied the rate of release of new technology fertilizers (i.e Polysulphate) presented a prolonged releasing pattern of up to 50 days and continuously supplied the crop with sulphate even after heavy rain events following application. The positive results from CRF and Polysulphate experiments have opened up a platform for further studies of their roles in reducing nutrient loss through leaching.