Fertilizer Management: Principles


Objectives of fertiliser management
Computation of fertiliser requirement
Balanced fertilisation
Potential nutrient losses and environmental concerns
Economics of fertiliser recommendations
Additional agronomic principles for young palms

Objectives of fertiliser management 

i) The objectives of fertiliser management in oil palm used to be straightforward as follows:

  • To supply each palm with adequate nutrients in balanced proportion to ensure healthy vegetative growth and optimum economic FFB yields.
  • To apply the fertilisers in the prescribed manner over the areas of the estate that are likely to result in the most efficient uptake of nutrients.
  • To integrate the use of mineral fertilisers and palm residues.

ii) However, the following conditions make achieving the objectives a challenge nowadays:

  • Shortage of reliable and skilled workers, and high turn-over in work force.
  • Environmental concerns which are related to over-fertilisation, land degradation, and pollution from heavy metals e.g. cobalt and eutrophication by P.
  • Expansion of oil palm into areas with little information on the soil properties, climate etc which are necessary for good fertiliser management e.g. the cultivation of oil palms on ultrabasic soils.
  • Managing larger manuring blocks which can result in over generalisation. In fact, this approach goes against the current trend of site-specific fertiliser management and precision agriculture.
  • Rising fertiliser prices which increase production costs.
  • Planting oil palm in countries where lack of clear law and order or understanding them can be a yield-limiting factor e.g. Indonesia and southern Phillipines.

iii) Therefore, the agronomic principles of an effective fertiliser management should take all the above into account and balance the above needs and objectives with the resources in the estates. The key steps are:

  • Determine the growth and yield targets.
  • Assess the nutrient requirements to attain the above and prevent the occurrence of nutrient deficiency.
  • Assess the management level and resources of the estate.
  • Ascertain the most efficient and cost effective fertilisers and applications of fertilisers to meet the nutrient requirements.
  • Compute the economics of the recommendations and expected results.
  • Monitor the outcome including the economic returns.
  • Decide on further action required and repeat the steps if necessary.

iv) Most of these steps should be covered by other lectures in this course but for completeness and comprehensibility of our lecture, we shall briefly discuss them.

Computation of fertiliser requirement 

i) There are several methods commonly used for the formulation of fertiliser recommendations. These include:

  • Critical leaf and/or soil nutrient level method
  • Optimum nutrient ratio method
  • Yield response function method and
  • Nutrient balance method

ii) In actual practice, derivation of fertiliser rates does not rely exclusively on any one method. An integrated approach, which combines the above methods, is usually adopted and AAR is one of its proponents.

iii) Primarily, the nutrient balance method is employed first to compute the nutrient requirements of oil palm in a manuring block. This approach assumes that the oil palm agroecosystem has definite components of nutrient removal (demand) from the system and nutrient return (supply) to the system (Figure 1). The components of nutrient demand are:

  • Growth
  • Yield
  • Nutrient losses through leaching, run-off and erosion
  • Nutrient removed by pest damage and
  • Nutrient non-availability and antagonisms.

The components of nutrient supply are:

  • Nutrient returns from the palms, e.g. pruned fronds
  • Nutrient returns from leguminous covers
  • Rainfall
  • Soil
  • Fertilisers

The basic principle is then to estimate the total demand of the palm and match it with the nutrient supply by the oil palm agroecosystem excluding the fertiliser component. The shortfall between the nutrient demand and supply, which is also called gross nutrient requirements, should be met by fertilisers.

iv) A number of studies have been made to quantify the various components of nutrient demand and supply in the oil palm agroecosystem.

v) The two largest components of nutrient demand are Growth and Yield. They are also the first key steps in an effective fertiliser management scheme as outlined earlier. Thus, it is essential that the agronomist estimates the growth rate and yield trend of a manuring block right from the start. A typical example of the growth rate of oil palm using leaf area as the criterion is shown in Figure 2. Coupled with the leaf nutrient concentrations, the agronomist will be able to estimate the nutrient requirements necessary to attain the expected growth. Similarly, the yield profiles in different regions of Malaysia as illustrated in Figure 3 will provide a clue on the nutrient removal per year from the manuring block which should be replaced by fertiliser inputs.

vi) On the nutrient supply side, available data suggests that atmospheric returns are probably insignificant. However, pruned fronds can provide substantial nutrients to the palms to the tune of 36% for N and 27% for K on poor inland soils in Peninsular Malaysia. In mature oil palm areas, the last component of nutrient supply is soils. Unfortunately, most Malaysian soils including those from Sabah are inherently poor in nutrients particularly N and P (Table 1). Therefore, most of the nutrients required by the palms have to come from fertilisers, usually in mineral forms.

  • An example of the computation of nutrient balance and fertiliser requirements to sustain 30 t/ha/yr in a mature oil palm field is shown in Table 2. It is assumed that the oil palm is in a steady state and grown on a soil with poor fertility. Under steady state condition, the canopy size remains constant and therefore, the nutrient requirements for canopy growth should be met by the nutrients recycled from the pruned fronds. The final analysis shows that the annual fertilisers needed for each palm to satisfy the gross nutrient requirements totalled 10.75 kg and comprise 4.22 kg Ammonium chloride, 0.97 kg Jordan phosphate rock, 3.59 kg Muriate of Potash and 1.97 kg Kieserite.

  • While the nutrient balance approach provides the gross nutrient requirement, it does not work out the fertiliser requirements directly. We need information from fertiliser trials to enlighten us on the optimum fertiliser rates and the yield responses. In Sabah, the oil palms respond mainly to N fertiliser followed by K and P fertilisers (Table 3). The response to N generally exceeds 15 % except on Lumisir Family soil. The latter might be attributed to its high inherent soil fertility status as indicated by the yields in the control plots (no fertiliser). K responses are mainly lower than those experienced in Peninsular Malaysia. Again, this can be explained by the relatively high soil exchangeable K status as shown in Table 1. These results strongly imply that the agronomist must know and understand the soil properties in the manuring blocks, not just the soil names, to draw up proper and effective fertiliser recommendations to the estates.

  • We can also predict the fertiliser efficiency in each trial by plotting the gross nutrient requirements against the fertiliser rates as shown in Figure 4 while Table 4 shows the fertiliser efficiencies in some coastal and inland soils in Peninsular Malaysia. The highest K fertiliser efficiency was in Munchong series soil at 83%. This was due to the poor soil K reserve and good yield response to K fertilization. The lowest fertiliser K efficiency was found in Briah series soil at 19% due to high fertiliser rates and soil K status. In general, fertiliser efficiency is affected by the gross nutrient requirement, imbalanced nutrition, fertiliser rates, soil fertility and nutrient losses.

  • Collating and assimilating the data from fertiliser trials conducted worldwide have enhanced the confidence of the agronomists to extrapolate the results to other sites with similar conditions and combining them with nutrient balance computation, leaf analysis and soil fertility status to produce the fertiliser recommendations.

Balanced fertilisation 

  • High fertiliser rates alone will not always provide optimum economic returns: a balanced fertiliser program is also essential as illustrated in Table 5. Nitrogen increased yield by 49% in the presence of high K rate. Similarly, there was a 25% yield response to K when high N rate was applied. Both N and K also had beneficial effect on the vegetative dry matter production.

  • Apart from the above, application of K fertiliser will decrease oil to bunch ratio in the absence of N fertiliser (Table 6). However, with sufficient N level, K fertiliser generally increased the oil to bunch ratio to similar level compared to the control.

  • Positive interactions of K fertiliser with other agronomic practices such as mulching, frequency of application and frond placement have been reported to increase yield between 4% and 14%.
  • While capitalising on synergistic effects will improve yield and fertiliser efficiency, avoidance of antagonistic effects is also necessary to maximise fertiliser use. For example, high K rates have been shown to depress Mg and B uptakes and might decrease yield.

Potential nutrient losses and environmental concerns 

The recommended fertilisers should be applied in a manner that they are absorbed by the palms at maximum efficiency. This is best done by minimising fertiliser losses in the plantation, which is even more important now in view of the current economic woes. It should also minimise environmental problems if any.

Nutrients may be lost by surface run-off, leaching through the soil profile, nutrients fixation, volatilisation and immobilisation by ground covers in young oil palm. An understanding of these nutrient loss mechanisms is essential to alleviate them and improve fertiliser efficiency.

i) Surface run-off

  • On average 11% of N, 3% of P, 5% of K, 6% of Mg and 5% of Ca applied can be lost in surface run-off alone (Table 7). These results were obtained during a low rainfall year with only 1426 mm on a 9% slope. The most susceptible areas for run-off tend to occur in the harvester’s path and along the oil palm rows where the soils are more compacted and the ground vegetation is generally sparse.

  • More recent data obtained by AAR also indicate that the mean run-off losses as percentage of the nutrient applied are within the following ranges: 5-8% N, 10-15% K, 4-6% Mg and less than 2 % for P (Table 8). These results show that soluble nutrients such as N, K and Mg are more susceptible to run-off losses. We further found that nutrient losses via surface run-off are highly dependent on the rainfall pattern at the time of fertiliser application, particularly during the first few rains after application and the antecedent moisture status of the soil. Other equally important factors, which might affect run-off, are the canopy cover, rainfall intensity and quantity, soil characteristics and slope.

ii) Leaching losses

  • Leaching losses during the first four years of oil palm growth (as % of total nutrient applied) have been found to be about 17% N, 10% K and 70% Mg. Losses are substantially reduced to about 3% N, 3% K and 12% Mg when the palms are fully matured (Table 9). The main reasons for the high leaching losses during the early stage of palm growth are probably poor palm canopy cover, less extensive root system and ground covers are generally not well established especially during the first year after planting.

iii) P Fixation

  • Losses due to fixation by the soil involve mainly phosphate fertilisers. The P fixing capacities of some of the common Malaysian soils are shown in Table 10. The amount of P ‘fixed’ ranged from 208 mg to 1172 mg per kg soil and is related to its clay mineralogy. Although soils with high P fixing capacity improve P dissolution of phosphate rock, they also decrease the soil solution P (intensity), which is required for plant uptake. The general approach is to use less reactive phosphate rock and concentrated application of fertiliser through high rate and banding for these soils.

iv) Volatilisation losses

  • Volatilisation losses are only significant when urea is surface applied, usually over the compacted weeded palm circles. High volatilisation losses in the oil palm field occurred at high rates of fertilization and on light texture soils as shown in Table 11.
  • To increase the efficiency of urea, it should preferably be buried in the ground. However this practice is only suited to small-scale cultivation and unlikely to be practical and economical on a large plantation. Correct timing provides a more suitable means to improve the efficiency of applied urea. For example, volatilisation loss is reduced if urea is applied when moderate rains are expected so that the fertiliser may be washed into the soil.

v) Immobilisation by ground cover in young oil palm

  • Weed growth is strongest in high light conditions in immature plantation. The young palms without extensive root systems are less able to compete for nutrients at this stage, which reduce their nutrient uptake and growth (Table 12). One point of interest is that the total N immobilised by the ground covers commonly exceeded run-off losses and immobilisation by young oil palms.
  • With respect to interrow vegetation management, spraying out the competitive weeds in the interrow vegetation at immaturity and maturity on Selangor series soil (fertile soil) gave the highest oil palm yields after 4 and 6 ½ years respectively. On the other hand, over spraying could lead to bare ground conditions which might cause higher leaching losses, reduce soil moisture and result in poorer soil structure. This in turn may lower FFB yield.

Economics of fertiliser recommendations 

  • The plantation industry is a business proposition and as such, the economic value of a fertiliser is important. This is because the application of fertiliser necessarily increases the cost of production, which has to be at least offset by an increase in yield in order to be profitable.
  • Owing to the delay in the effect of fertiliser on yield, the additional return from the increased yield may be realised in full only after 8 months or even a few years. Furthermore, the magnitude of yield response may vary considerably and the economic comparisons of fertilisers should be based on a discounted cash flow or a similar scheme over the specified period.
  • An example of the economic computation of two sources of fertiliser is provided in Table 13. We choose kieserite versus ground magnesium limestone (GML) to illustrate the point that knowing the agronomic efficiency of a fertiliser as obtained from fertiliser trials is insufficient to recommend its application. Table 13 shows that the agronomic efficiency of GML based on substitution rate was only 74% as effective as kieserite. However, GML was only one-third the price of kieserite at the time of writing. This favoured GML with the consequent relative economic efficiency reaching 2.5. This meant that GML was 1.5 times more efficient compared to kieserite in economic terms.
  • Using the above approach, an expensive fertiliser may be more economical to use if its agronomic efficiency far outweighs its price ratio compared to its competitors.
  • Although the above computation is a standard in economics, of late there are counter arguments which suggest that the selection of a fertiliser should be based on its agronomic efficiency instead of economic efficiency. This contrasting proposition stems from the fact that commodity prices are usually unpredictable and therefore, the economic efficiency can vary substantially. Such view is probably a fallacy since decision-making processes in agriculture, like all businesses, are always done in the face of uncertainty, be it prices or weather etc. Moreover, the use of tender fertiliser prices will allay or negate part of the problems. In plantation agriculture, profit considerations are given the highest priority and therefore, the economic efficiency will always take the centre stage.

Additional agronomic principles for young palms 

The strategy in young palms, apart from the above, should be:

  • To minimise nutrient requirements by maximising returns from the biomass of the previous crops e.g. rubber, cocoa or oil palm by the shredding and no-burn techniques currently practised in many plantations.
  • To promote growth of very good leguminous covers with high P and Mg applications and subsequent large nutrient return including N fixed.

Such an approach would reduce fertiliser requirements of the young palms substantially and improve growth and yields, thereby leading to extensive benefits all round.

Reference
Goh, K.J., Teo, C.B., Chew, P.S. and Chiu, S. B. (1999) Fertiliser management in oil palm: Agronomic principles and field practices. In: Fertiliser management for oil palm plantations, 20-21, September 1999, ISP North-east Branch, Sandakan, Malaysia: 44 pp

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

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