Fertilizer Management: Current Challenges

Some current challenges and future trend

The fertilizer management system described thus far can be regarded as traditional method commonly adopted in the oil palm plantations. It has served the industry well as evidenced by the high FFB yields, respectable returns to manuring and sustainability. But, the industry now faces many new challenges and some of them are briefly discussed below.

Labour requirements

The current plantation management system is labour intensive and many of them are deployed in manuring work. Switching to mechanical spreading of fertilizers will immediately result in tremendous saving in labour requirements but the following principal points should be noted (Chew et al ., 1994a):

•  Application efficiency increases when roots system of oil palms are adequately developed and spread out

•  Avoid application over eroded and compacted areas traversed by in-field vehicles which suffer severe run-off

•  Limited to areas of suitable terrain and soil types which can take vehicle load

Apart from the above points to consider, there is usually a lack of control in actual fertilizer application rate with mechanical spreader since the speed of tractor is variable and the actual traverse path of the tractor is determined by the driver. Both difficulties can probably be overcome with electronic controller and GPS.

Other responses to the high labour requirements for manuring are to reduce the frequency of application to once a year e.g. the use of FELDA or AA+ Mulch TM for mature palms (Figure 1), effective sources of fertilizers, improving nutrient holding capacity of the soils and better nutrient uptake by roots. Recent results showed that applying fertilizers under the FELDA Mulch resulted in better leaf and rachis P and K concentrations of oil palms compared with broadcasting in a high rainfall region in Sarawak (Figure 2). This system reduces surface run-off and erosion of applied nutrients and avoids excessive concentration of applied nutrients at a spot. Therefore, it allows the application of fertilizers during wet weather. This method also provides better flexibility in the manuring programme and utilization of labour. However, the long-term economic returns from this system are still being evaluated.

Figure 1: Experimental testing of FELDA mulch for mature palms to reduce the frequency of fertilizer application and surface run-off losses of nutrients.

Source: Lee et al . (2008)

Figure 2: Effects of methods of fertilizer application using FELDA Mulch (FM) and broadcasting (FSP) on leaf and rachis nutrient concentrations of oil palms. Trial was layout in a high rainfall region in Lundu, Sarawak (FASSB, unpublished)

Fertilizer prices

The volatile fertilizer prices in the past two years have been described as a “perfect storm” in IFDC report, Volume 33(4), December 2008. According to the report, numerous factors converged simultaneous to cause fertilizer prices to soar and then suddenly collapse. The latter was attributed to “demand destruction” when farmers were unable or unwilling to pay two to three times the prices of early 2007. The report further stated that the situation worsened with the collapse of the global credit market, a trade recession and slowdown in world economic growth. This depressing scenario of the fertilizer market for at least the next two years is nothing new as it has happened on a number of occasions in the past although the factors causing them might vary.

The first reaction of most farmers and planters to high fertilizer prices is generally to withdraw fertilizer inputs for better cash flow. However, as advised by Dr. Ng Siew Kee in the 1970s, we should look inwards first and examine various scopes to improve fertilizer use efficiency for greater economy in fertilizer usage. This would include adapting the various methods to fully utilize the by-products in the mill on a large scale in a practical manner as another source of soil amendments and fertilizers and not fertilizer substitutes or waste products. Thus, their agronomic and economic values must be painstakingly computed as shown in Goh et al . (1999). Any potential wastage in the fertilizer management system such as luxurious fertilizer regimes for the sites, poor fertilizer quality and incorrect timing of fertilizer application must be strictly attended to immediately.

The next step is to be fully aware of the factors affecting the economics of fertilizer usage as provided by Hew et al . (1973) and Lo and Goh (1977). Some of the major factors in the computation are the base yield, fertilizer response, discount factor, prices of palm oil and fertilizers, and agricultural risk. These factors are site dependent i.e. soils, palm age, climate and their interaction with nutrients and thus, it should be the agronomist who determines the quantum and where fertilizer should be reduced to meet the company’s cash flow and anticipated profit. Ng and Goh (2003) also showed that the type of agricultural risk to be taken depends on the economic situation and cash flow of the company. Under tight cash flow or low profitability, risk preference approach is probably the best option.

In determining the fertilizer response curve, the agronomist should calculate the impact of both fertilizer withdrawal and subsequent re-application of fertilizer. An example is illustrated in the self-explanatory Figure 3 where seasonal trend has been removed.

Figure 3: Predicted effects of fertilizer withdrawal and resumption on FFB yields in Malaysia using AAR’s combinatorial model. Source: AAR (Unpublished)

The main features to note in this graph are:

•  The decline in yield depends on palm nutritional status, soil fertility and time

•  There is a time lapse of about a year before a linear decline in yield is observed

•  The minimum yield depends on soil fertility and palm age

•  The recovery rate depends on palm nutritional status

•  When the palm is severely malnourished, its maximum yield is about 10% below its potential even after full recovery (Warriar and Piggott, 1973; Caliman et al. , 1994). The reason for this is still uncertain.

Reducing fertilizers or totally withdrawing them for economic reasons should always be a last resort because some yield loss will ultimately happen and the economic optimum is usually not achieved. However, it will relieve the cash flow problem of the company because fertilizer cost is the largest operational cost in managing an oil palm plantation. Thus, if fertilizer withdrawal is absolutely necessary, the following strategy might be followed but it certainly require a competent agronomist to implement it correctly:

•  Select the nutrient with the least impact on FFB yield (revenue depends on prices and thus difficult to target)

•  Any cheaper sources?

•  Select soil types/fertility with lowest FFB yield response to the nutrient

•  Select the climatic zone with least impact on FFB yield

•  Select palm age category with least impact on FFB yield

•  Go to step (a) until objective is achieved

This strategy will choose the category of palms for fertilizer withdrawal and the nutrients and quantity to be withdrawn that will result in the least impact on FFB yield allowing quicker recovery when the economic situation improves. It is also site-specific. Thus, it is superior to the usual strategy of many companies to cut fertilizers by a certain margin across the board, which may lead to drastic yield decline in areas with good fertilizer responses.

Sources of fertilizers

In 2007, urea accounted for more than 50 % of the world N production (excluding ammonia). This is also true in Malaysia where urea and urea-based fertilizers will take the lion share of the N market although in the oil palm industry, the converse may be true. The latter was due to the unpredictable N volatilization losses on inland soils which deter most agronomists from recommending it widely. If the N volatilization losses can be controlled to a predictable, narrow range for each environment, then it is possible to use urea as a main source of N for oil palm on inland soils whenever it is cost effective.

Currently, many methods are available to reduce N volatilization losses from urea such as urease inhibitors, S-coating (perhaps using 10% S only since Malaysian soils are generally acidic), humic acid, K and B. Also, slow release fertilizers and bio-fertilizers which are urea based are being marketed in Malaysia. We should conduct proper, well replicated trials to evaluate their effectiveness for oil palm on inland soils. Another way to stop or minimize N volatilization from urea is to apply it under AA+ Mulch TM or FELDA Mulch.

There is also a growing interest in bio-fertilizers because of the premise that the soils under oil palm are relatively sterile due to long-term fertilizer usage, and the effective microorganisms (EM) in bio-fertilizers can rejuvenate the soils leading to improve soil fertility and subsequent better productivity. Microbes are the unseen majority in soils but despite their abundance, the impact of soil microbes on ecosystem processes is still poorly understood (van der Heijden et al ., 2008). The latter workers, in their extensive review, concluded that soil microbes must be considered as important drivers of plant diversity and productivity in terrestrial ecosystems. Despite this enthusiasm, there has been no conclusive evidence that introduced EM improve crop productivity in the fields. Similarly, Blal (1989) working on the effectiveness of vesicular-arbuscular endomycorrhizas on oil palm showed that it was only effective on sterile soils. Nevertheless, this new area of research should be explored albeit at a lower level to provide data on the best route to take.

Fertilizer quality

Fertilizer quality has always been a concern to the industry. Although we have SIRIM standards, they were drawn up at a time when fertilizer prices were relatively low. With the current high fertilizer prices and the improvement in laboratory techniques and fertilizer manufacturing technology, it is perhaps logical or even warranted to call for a review of the standards particularly those related to compound fertilizers and fertilizer mixture. Also, newer experimental data are now available to assess the effectiveness of various fertilizers such as rock phosphate (Chan and Goh, 1997a, Zin et al ., 2001) which should be incorporated into the standards.

RSPO

The creation of RSPO has added another dimension to the many aspects of an agronomist’s roles because fertilizer management is part of the Principles and Criteria of sustainable palm oil under Principle 4.2. This Principle states that soil fertility should be maintained or improved to a level that ensures optimal and sustained yield by monitoring the trend of soil organic matter and net fertilizer inputs. As expounded earlier, this has always been a feature in the conventional fertilizer management system of oil palm.

Ng et al . (2004) showed that soil organic C decreased with time in the oil palm plantation during the period when the oil palm biomass was allowed to be burnt or partially burnt at replanting. However, large increases in soil organic C occurred with the current zero burnt replanting technique in the first few years. This positive change has not been traced over the life cycle of oil palm and moreover, there is currently no conclusive evidence to show that the improved soil organic C will lead to better or sustained productivity/yield of oil palm to the best of our knowledge. This provides a golden opportunity for researchers to undertake the study in order to understand the mechanism and impact of this important subject matter.

Chew et al . (1994a), Kee et al . (1995) and Ng et al . (2004) demonstrated that soil pH will decline at localised area in the oil palm agro-ecosystem such as the palm circle due to the use of acidifying N fertilizer. However, it does not appear to affect the productivity of oil palm. There is also a strong build-up of soil P and K especially in the palm circle in order to maintain adequate solution P and K for optimal uptake of these nutrients by the palms. We need to develop some methods to improve the uptake of these nutrients in the palm circles by the palms perhaps by increasing soil organic matter and/or soil pH or through soil microbes.

Chew et al. (1994a) in their review clearly showed that leaching losses of nutrients under oil palm were relatively low. This was supported by Foong (1993), Omoti et al . (1983), Schroth et al . (2000) and recent unpublished work at AAR where the latter showed non-significant difference in solution nitrate concentrations between the optimal N rate and without N input at 120 cm depth after 18 years of differential fertilizer treatments (Figure 4).

Figure 4: Leaching losses of nitrate under oil palm on an ultisol after 16 years of differential N inputs. Source: AAR (Unpublished)

Chew et al. (1994a) and Kee and Chew (1996) also showed that the off-site effect of applied nutrients, which are mainly in the forms of run-off and erosion, were generally low at less than 15% if they were applied during suitable months for fertilizer application. The major concern here is the lack of data to assess the impact of these processes in hilly areas on the environment and fertilizer use efficiency. Nevertheless, Chew et al.(1994a) concluded that the major risks to the environment arise from the following:

•  At times of clearing for oil palm planting with the large release of soluble nutrients especially K from old stand of oil palm

•  Over-application of fertilizer to young palms before full development of the root system or full growth when leaching losses are highest. Split fertilizer applications are very important at this stage to improve nutrient uptake efficiency.

These two aspects of oil palm cultivation are currently subjects of active research in Malaysia.

Of interest to many researchers now is the maintenance or improvement of soil quality. In fact, in highly weathered and degraded soils of the tropics, the latter is more important to sustain high yield and profitability. However, the definition of soil quality is still subject to much debate. Nevertheless, RSPO indirectly stated that soil quality includes structure, organic matter content, nutrient status and microbiological health of the soil. While the definition of soil quality may not be the most important to our industry, we should still establish quickly some practical agro-biological indicators of the soils that have significance on the fertilizer management and sustained productivity.

Climate change and variability

Climate change and its variability have existed since time immemorial. A large proportion of these changes is natural and involves geophysical processes. However, the main concern now is the rapid rate of climate change globally that is detected recently and generally attributed to anthropogenic causes. The evidences for the latter thus far especially in the long-term have been scientifically weak. In fertilizer management of oil palm, our main concerns are the impact of fertilizer use on

•  greenhouse gas (GHG) emission

•  soil C build-up

•  energy use

In GHG emission, it is probably only relevant in “wet” soils where the risk of anaerobic conditions is higher with consequent methane and nitrous oxide emissions. Melling et al. (2006) showed that the application of urea to oil palm on deep tropical peat only resulted in a short-term emission of small amount of methane in the month of application (Figure 5).

Figure 5: Monthly CH4 flux before and after urea application at the oil palm plantation. Data represent mean ± standard error (n = 3)

Source: Melling et al. (2006)

The effect disappeared two months after urea application. This short term effect was ascribed to reduced oxidation of methane due to its inhibition by NH 4 + ion which was produced when urea hydrolysed. Urea application to deep tropical peat under oil palm has no significant effect on nitrous oxide emission (Melling et al. , 2007). Although these results showed that urea has little or no role on GHG emission from tropical peat under oil palm, further work is necessary for a firm conclusion to be made.

Fertilization has been shown to enhance the productivity of oil palm with consequent better rooting system of more than 12 t dry matter per ha. However, the sequestration of this organic matter to soil organic C in different environments is still uncertain. There is also a lack of data on C sequestration from the various sources of organic matter produced by the oil palm e.g. pruned fronds, EFB, POME and decanter cake, and the leguminous cover crops. This information has a large bearing on the C cycle of oil palm and its impact on climate change.

The energy balance of oil palm has been estimated by a few workers such as Wood and Corley (1993), Reijnders and Huijbregts (2008) and Wickeet al . (2008). However, they generally did not include the latest technology of fertilizer production which is more energy efficient (de Vries, 2008), the increasing use of locally manufactured urea based fertilizer and recycling of oil palm biomass residues and mill by-products and thus, probably grossly over-estimated the energy use in oil palm plantation. It is critical that a new life cycle analysis (LCA) of the energy balance of oil palm be made in view of the pressing need to correctly inform our buyers, consumers and NGOs with scientifically based data.

Competent agronomists

The current and future crop of agronomists has a formidable task not only to improve fertilizer use efficiency and palm oil yield but also meet the many challenges listed above and future work below. Thus, they must have the leadership and creativity to meet these challenges and the courage and commitment to pursue and persevere towards their convictions and maintain the highest standards possible. The ability to adapt to change and avoid self ego is essential if we are to maintain our edge over the competing vegetable oil crops in the long run. Also, the agronomists are now regularly requested to evaluate untested products for the plantations. They must maintain their integrity and based their decisions on scientific ground and guiding principles of soil and plant nutrition, and do not allow friendship and emotion to cloud their judgement. The other roles of agronomists were well described by Chan and Goh (1997b) and Chew and Goh (2003). The cooperation between agronomists from different organisations should continue to be fostered and joint research work initiated to solve problems of common interest. With the rapid expansion of oil palm worldwide, the number of agronomists required has also increased correspondingly and the lack of competent agronomists is becoming apparent. The industry will do well to provide the necessary atmosphere, coercion, training, facility and remuneration to attract the best and ensure that this unenviable task is under good hands.

Reference:

GOH, K.J., G, P.H.C. AND LEE, C.T.: Fertilizer Management and Productivity of Oil Palm in Malaysia

The full list of references quoted in this article is available from the above paper.

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