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Water and nutrient losses through runoff and leaching are the main factors limit soil fertility and water availability for sustainable crop production especially on sloping lands. Therefore, Proper soil and water conservation practices are needed to minimize such losses to maintain and improve soil fertility and its productivity for plant growth. Organic mulches (Empty Fruit Bunches (EFB) of oil palm, Eco- Mat and palm fronds) and silt pit are among the recommended conservation practices to reduce surface runoff and improve soil chemical and physical properties and water content which are important in maintaining soil fertility and productivity.
Numerous studies have shown EFB application had increased oil palm's vegetative growth, nutrition, and yield (Chan and Goh, 1978; Lim and Pillai, 1979; Khoo and Chew, 1979; Singh et al., 1981; Loong et al., 1987; Lim and Chan, 1987; Lim and Zaharah, 2002), as well as increasing the soil's organic matter content, pH, and nutrient content (Chan et al., 1980; Rosenani and Wingkis, 1999; Zaharah and Lim, 2000; Lim and Zaharah, 2002). Information on the effects of Eco-Mat and silt pit on soil properties is limited. However, a study (Wan Asma, 2006) showed that Eco-mat increased soil moisture, plant growth and N, P and K uptake by Acacia. MPOB (2003), and Khalid and Tarmizi (2004) reported that young oil palms planted on hill terraces with Eco-Mat mulching showed higher growth rates and higher uptake of N, P, and K nutrients than those without Eco-Mat mulching. In an experiment carried out in India (George et al. 2003), it was shown that silt pit was effective in conserving soil (13.94 t/ha) and soil nutrients of N, P and K up to 34.16, 18.11 and 25.09 kg/ha respectively. Lim (1989) also reported 23 % reduction in soil loss due to the silt pit in an oil palm plantation on sloping lands.
Water and nutrient losses through run off and leaching are among the main factors limit soil fertility and water availability for crop production especially on sloping lands. Therefore, proper soil and water conservation practices are essential to minimize such losses to maintain and improve soil productivity. To reduce water and nutrient losses, several methods are used. One of them is the use of oil palm empty fruit bunches (EFB) as a natural mulching material. In spite of the beneficial effects, one well-known disadvantage of EFB is it is bulky, making its transportation, storage, and distribution difficult and expensive. One recent method is to compress the EFB into a mat or carpet known as Eco-Mat. Being less bulky, storage, transportation, and handling of Ecomat is easier and cheaper than EFB. Moreover, because Ecomat is more aesthetically pleasing than EFB, Eco-Mat is more marketable and a better choice as a mulching material for landscaping purposes in urban areas. The use of Ecomat gained wide public attention, for example, when China imported Eco-Mat from Malaysia as a landscaping mulching material to be used during the Beijing Olympics in 2008.
Other than EFB and Ecomat, another method to conserve soil water and nutrients on oil palm hill slopes is to construct silt pits, where long and wide trenches are dug into the soil somewhere between the planting rows and in perpendicular to the hill slope so that these trenches collect runoff water and soil. The idea is so that these silt pits act as storage areas, preserving the soil water and nutrients that would otherwise have been lost through run-off. These trenches then help to redistribute the collected water and nutrients back into the plant roots after a rainfall event. Although much have been researched on the effects of EFB (but to a much lesser degree for Ecomat and silt pit) on soil properties, there is no single study, to our knowledge, that compares the effects of these three soil and water conservation methods on soil properties.
On the other hand, a large amount of oil palm residue produced every year (about 52 million tonnes pruned palm fronds, about 20 million tonnes EFB in 2008) mostly used as mulching materials. Therefore this study would be informative and helpful to find the best soil conservation practices and relative effects of these practices on soil fertility and water conservation especially on sloping lands.
The main objectives of this study are to:
1- Examine the effects of natural mulching materials (palm fronds, EFB and Eco Mat) and silt pit on soil fertility and water content in an oil palm plantation.
2- Develop a computer model to Simulate soil water content under different conservation practices and predict the effects of different levels of water stress on oil palm growth and yield.
Material and Methods
This research is conducted in a field located at Balau Estate (2° 56 57 N, 101° 53 56 E), Semenyih, Selangor for two years since Dec 2007. The experimental layout is a split-split block arranged in a completely randomized block design with three replications. The conservation practices (CP) including EFB, Eco-Mat, silt pit and palm fronds as a control were allocated to the whole plots, soil sampling times (T) and soil depths (D) were considered as sub- and sub-sub plot respectively. The silt pit dimension is 4 - 1 - 0.5 m in length, width and depth respectively. EFB was applied as 1000 kg per plot and four pieces of 2 - 1 - 0.02 m of Eco-Mat were placed on the soil surface between the oil palm rows. Pruned oil palm fronds were stacked between planting rows was considered as control. EFB and Eco-Mat reapplied each year in January. Soil samples from three depths, 0-15, 15-30 and 30-45cm have been taken in the middle of each EFB and Eco-Mat treatment plots and 0.5 m away from the silt pit and palm fronds plots every three months for two years from Dec 2007 until Dec 2009. The samples then were analyzed for soil aggregate size distribution by dry-sieving method (Kemper and Rosenau, 1986), aggregate stability by wet-sieving method (Kemper and Rosenau, 1986), pH using pH meter with soil to water ratio of 1:2.5 (Mc Lean, 1982), CEC by leaching method using 1 N neutral ammonium acetate (NH4OAc) solution (Thomas, 1982), Total carbon by dry combustion method using Leco-412 carbon analyzer (Skjemstad and Baldock, 2008), total N by Kjeldahl method (Bremner and Mulvaney, 1982), available P by molybdenum blue method using Bray and Kurtz No.2 extracting solution (Olsen and Sommers, 1982), available K, Ca and Mg by Leaching method using 1 N ammonium acetate (NH4OAc) solution (Knudsen et al, 1982). Soil bulk density was measured for 0-15 and 15-30 cm soil depths by core ring method (Blake and Hartge, 1986). Soil water content of each treatment up to 75 cm depth and at 15 cm increments was measured every day using a soil water profile probe (PR1, Delta-T, Cambridge, England). To determine plant nutrient status of the oil palm, frond No. 17 was sampled every six months and separated to leaflet and rachis and analyzed for P, K, Ca, Mg, Fe, Mn, Cu and Zn by dry ashing method (Jones, 2001) and N by Kjeldahl method (Bremner and Mulvaney, 1982). The data was analyzed statistically by SAS software () and protected LSD was used to separate means.
Results and discussion
This experiment is still ongoing but the first year results showed that soil pH, total C, exchangeable-K, Ca, and Mg, aggregate size distribution and stability were significantly affected by the conservation practices. However, soil total N, C:N ratio, CEC and bulk density were not affected. Mean separation test by least significant difference (LSD) showed that EFB improved soil fertility by increasing both soil chemical and physical properties including PH, total C, exchangeable- K, Ca Mg, aggregate size distribution, aggregate stability significantly higher than the other conservation practices and soil water content by as much as 37 %. EFB also increased rachis K content significantly higher than other conservation practices and leaflet P, Mg and Mn contents significantly higher than control. Eco-Mat, however, was not as effective as EFB in increasing soil chemical properties, its effects on soil physical properties and leaflet P and Mn was nearly the same as EFB. Silt pit was as effective as EFB in increasing soil and plant P and plant Mg and Mn contents. However, it was not significantly different from control in most of the soil properties and from Eco-Mat in most of the soil properties and plant nutrient contents. There was no significant effect due to the conservation practices on plant leaflet N, Ca, Fe, Cu and Zn contents.
So far EFB was found to be the best to improve soil fertility, soil water content and oil palm nutrition on the sloping land oil palm plantation.