Soil variability-based irrigation system for oil palm plantation

Irrigation has been treated uniformly in oil palm fields, whereas soil water holding capacity can vary spatially across a field, resulting in either over or under water supply. This study evaluated an irrigation system in an oil palm plantation based on the variability of soil water holding capacity, which served three specific objectives. The first step is to define soil water holding capacity to create an Irrigation Management Zone (IMZ). The low-cost emitter for the micro-sprayer was then defined and used in irrigation planning with the IrriPro software. Finally, each IMZ was verified using oil palm yield, growth, and water usage. A grid system was applied for soil sampling using a 100m x 100m distance within the 20.3 ha study area, consisting of three soil depths up to 90 cm. In the laboratory, soil physical analysis was conducted and Available Water Holding capacity (AWHC) was determined using pressure plate analysis. The AWHC was delineated using Geographic Information System (GIS) software and the Kriging method. Several hydraulic emitter tests were conducted to provide additional data for the IrriPro software. IrriPro software was used to simulate and evaluate water uniformity. The Soil Variability-Based Irrigation (SBI) System, which is equipped with a tensiometer was installed according to IMZ. Meanwhile, soil infiltration rates were measured for each IMZ and analysed using Food and Agriculture Organisation - CROPWAT (FAO-CROPWAT) software. Following that, the FAO-CROPWAT 8.0 software was used to simulate estimated irrigation depth (EID) and total net irrigation (TNI) for 2016 and 2017. Recording plots were established in Zones A and C to measure yield and growth. Finally, water usage and Water Productivity (WP) were calculated for specific zones. The results showed that clay, sand, and organic matter (OM) distribution varied with soil depth. However, no significant correlation was found between these variables and AWHC. IMZ was divided into three zones: A, B, and C, with AWHC range of 79 to 167 mm. The highest uniformity for the SBI system was 85% for Christiansen's Uniformity (UCC), and 66% for Emission Uniformity (EU), and the system was deemed 'Good' by Statistical Uniformity (Us). Soil infiltration rates ranged from 1.01 to 8.23 mm hr-1, with Zone C among the lowest. The low-cost emitter has a flow rate of 39-125 L hour-1 and a maximum throwing distance of 1.47-2.74 m. According to estate data, EID for 2016 went below the TNI requirement of 73 to 93 mm. In contrast, EID was nearly 55 to 90 mm above TNI in 2017. Zone A had a significantly higher cumulative yield (75.5 t ha-1), followed by Zone C (69.1 t ha-1), and finally the non-irrigation (NIR) plot (51.4 t ha-1). Palms in Zone A had higher growth rates in height, leaf area, frond production, canopy length, and Petiole Cross-Section (PCS). A linear regression line analysis with PCS revealed that actual dry frond biomass had an R2 of 0.713. Zone A had a significantly higher Crop Growth Rate (CGR) of 208 kg palm-1 year-1 and a higher Bunch Index (BI) than Zone C and NIR plots. Zone A used 9.72 m3 palm-1, while Zone C used 13.28 m3 palm-1 during the observation period, with the latter having significantly more irrigation events. Zone A had a higher WP (2.37 kg m-3) than Zone C and NIR. Based on simulation cost analysis, the SBI can provide a payback period of 4.5 years with a 5% Return of Investment (ROI) and a net present value (NPV) of RM 14,419. This study found that the IMZs were satisfactorily classified, indicating that lower AWHC required more water and irrigation events.

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