Application of fertilizers is a standard practice in the countries where A. mangium is a major plantation species. In most cases, however, the nature of fertilizers and their quantity are not based on systematic research. Fertilization levels and time of application have been decided tentatively, probably based on a few studies or on experience with other species in the area.
The main aim of fertilizer application is to produce uniform, fast-growing plantations. Uniformity makes it easier to prescribe operations (thinning, pruning) on time; fast growth ensures that the site is quickly captured. A few examples of fertilizer trials are given below.
1. SAFODA adopted the following fertilizer regime for A. mangium plantations:
• Apply 113 g of a Christmas Island Rock Phcsphate (CIRP) in each planting hole at the time of planting.
• Apply 57 g of NPK-BC 12:12:17:2 + TE to each plant 3 months after planting, placed equally in two holes opposite each other at about 1523 cm from the stem.
• At 8 months, broadcast 113 g of NPK-Bluc around each plant at least 15 cm from the stem.
• Finally, at 18 months increase the dose per tree to 170 g of NPK -Blue on sites showing poor growth (Raymond Tan 1992).
2. Wan Rasidah et al. (1989) concluded in Malaysia that the soils are low in nutrients, especially in phosphorus. A number of fertilizer trials have been carried out to determine the best schedule for fertilizers. Table 7.8 summarizes diameter and height growth responses for three fertilizer trials. Best response was recorded where compound fertilizers (such as NPK-Bluc 12-12-17-2+TE) were applied, although responses tend to be short lived and exhibit the gain in about 6 months. This helps in terms of faster canopy closure, reduced fire risk, and shorter rotation (Miller and Hepburn 1989; Mead and Speechly 1989).
In Bengkoka (Sabah), 90-100 g of CIRP is applied at the time of planting, followed by 45 g of NPK mixture 2 months later at the time of first weeding. Further application of fertilizer may be needed, according to Udarbe and Hepburn (1987).
Table 7.8. Growth comparison of fertilizer treatments at different ages (months).
Site/Treatment 6 12 16 19 25 31 36 5 6 9 12 20 25 31 36
Tanjung Piling Phosphate trial
• 469 g Rock P 1.46 applied to planting hole
• 110 g RP at 1.58 planting + 340 g NPK blue over 3 yrs
• 2001gP2O5/ha broadcast at planting
• 50 g/tree NPK blue applied at 2 months
Tanjung Piring Extra NPK blue trial
PSP Averages for _ 1.5 __3.0 3.5 5.5 7.5 9.5 _ 1.5 _ 4.5 6.0 7.5 9.0
Source: Miller and Hepburn (1989)
3. For the CFPP in Peninsular Malaysia's ex-jungle sites, Mead and Speechly (1989) recommend the following fertilizer schedule for A. mangium on the basis of preliminary studies:
• Broadcast-burnt sites require no fertilizer.
• For semi-mechanically prepared sites, apply a total of 100 g triple superphosphate (TSP)/tree between ash beds at planting in two slits 15-20 cm from the seedling. Apply a second dressing of 150 g TSP in a ring about 0.3-1.0m from the tree at 5-6 months. On erodible sites, this dressing should be applied at 3-5 months and covered with soil.
• For log-landings, increase the second dressing to 250 g/tree, and also rip the site to a depth of 60 cm.
On less fertile Imperata sites, such as at Bengkoka, they found it useful to add N and a general trace element mix to the P applied at planting. For example, the results of a trial on a Tanjung Lipat soil at Bengkoka showed that the best treatment resulted in a 4-month gain in diameter growth (Figure 7.4). They suggested replacing the initial fertilizer dressing with 120 g of a 1:1 mixture of TSP and NPK blue (12:5:14+TE). There was no recommendation whether the second dressing should contain nutrients other than P.
In Kalimantan, the following fertilizer trials have been conducted:
• A. mangium planted December 1987, fertilized January 1988 with triple superphosphate to supply 0, 5. 10, 15, or 30 kg/ha P, 12 kg/ha N + 10 kg/ ha P and 10 kg/ha each of N, P, and K (Adjers and Luukkanen 1988). After three months, fertilizer treatments had no effect on survival in this short-term trial. Although triple superphosphate significantly improved height growth over no fertilizer, the major response was to the mixed fertilizers. The NPK mix improved height development by 260% and mean diameter by 184%.
• A. mangium planted December 1987, fertilized February 1988, testing mechanical soil preparation vs. herbicide treatments with and without fertilizer (20 kg/ha P as triple superphosphate). Fertilizer clearly improved growth of the trees.
A. mangium planted June 1991 in a short-term trial (1 x 1 m spacing) adjacent to the Banjarbaru nursery to test 5, 10, 20, and 40 g P per plant
Figure 7.4. Response in diameter growth to fertilizer (113 g Christmas rock phosphateapplied in planting hole, followed by 57, 113, and 170 g NPK plus trace elements applied at 2, 8, and 20 months, respectively) at Bengkoka, Sabah. Source: Mead and
as triple superphosphate, and as rock phosphate Lime at 210,420, 840, and 1,680 kg/ha were applied, respectively, in addition to P5, 10, 20, and 40 treatments (triple superphosphate). A control (no fertilizer) was also included. By December 1991, satisfactory establishment had been achieved.
In Dongmen, China, a regime of 100 kg/ha N, 50 kg/ha P, and 50 kg/ha K was applied to an A. mangium plantation resulting in 179% increased volume production at age 2.6 years (Simpson 1992).
It is apparent that application of suitable fertilizers in adequate amounts at the proper intervals has great potential to increase early growth of A. mangium. Certainly, more intensive research is needed, as both the type and amount of fertilizer will vary with soil and other site conditions. For example, in Malaysia, P appears to be the most important nutrient, while in Kalimantan, K appears to be the limiting factor to growth. The first step in any comprehensive research on species fertilizer requirements is to identify the nutrient(s) likely to limit growth on a particular site. Such a research program needs to use foliar analysis combined with soil properties.
Fertilizer application inevitably adds to the cost of raising plantations. It is therefore essential to prove that the cost incurred by fertilizers is commensurate with gains in terms of survival, growth, and yield.
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