Modelling of water and solutes in permanent raised beds

Modelling of water and solutes in permanent raised beds

Permanent raised beds (PRB) are an agricultural cultural method that can improve crop productivity and health of soils. Australian Centre for International Agricultural Research (ACIAR) has funded a number of projects in developing countries but was concerned that the short-term benefits may be at the cost of longterm losses due to solute pollution of groundwater or salinisation of the beds. A modelling study was undertaken to consider the water and solute flow in raised beds in relation to the soil physical properties to improve understanding of the PRB system. HYDRUS(1D, 2D/3D) was used as the modelling platform. The domain used for the simulations is shown in figure 1. The results show that a simple model for infiltration into the raised beds is useful for estimating the width of the raised bed for most soils especially if the sorptivity was measured on a trial bed. Compaction of the furrow between the beds commonly occurs due to vehicle traffic. Compaction under the furrow was simulated and this showed that water penetration horizontally was slowed as cumulative infiltration with time was reduced. However, for the same amount of cumulative infiltration the penetration horizontally was greater than when no compaction occurred. Drainage of the beds when an impermeable layer occurs in the soil shows that a simple inversion of the moisture characteristic relationship could be used to estimate the water potential profile in the bed. This also shows that for clay soils the beds must be excessively high for them to drain effectively through seepage to the furrow. The leaching of fertilizers by furrow irrigation was investigated to determine at what distance from the furrow fertilisers should be placed to reduce leaching during irrigation. This distance was shown to be soil dependent. Salinisation due to evaporation from a shallow water table is likely to occur if a saline watertable occurs at < 0.5 m in sand and < 1.5 m in loam and clay soils unless properly managed. (Graph Presented).

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