Abstract
The effects of soil tillage/compaction (tillage and compaction, TC; no-tillage and compaction, NT-C; tillage, T; no-tillage, NT) and dry season irrigation on soil properties, nutrient status and oil palm root system growth were investigated in small field plots for two years after transplanting the palms. Tillage was manual to a depth of 30 cm and compaction was by rubber tyres of an unweighted Massey Ferguson 265 tractor. Bulk density and cone resistance increased in the order T, NT, NT-C and TC in the 0-30 cm layer. Compaction tended to enhance moisture retention both with or without irrigation. In the 0-30 cm layer, concentrations of organic C, total N and exchangeable Ca in the T plot higher than the other plots were due to relatively large amounts of these elements in the T-with-irrigation subplot. Exchangeable Mg was highest in the TC plot; available P and exchangeable K were not affected by tillage/compaction but K tended to increase with compaction. Soil pH was lowest in the NT plot, probably due to low Ca. The nutrients were not affected by tillage/compaction in the 0-150 cm profile. Irrigation increased total N in the 0-30 cm layer and decreased exchangeable Mg in both the 0-30 cm and 0-150 cm layers but did not affect other nutrients. Leaf N (%) increased in the order TC, NT-C, NT and T; differences between TC and T were significant. Tillage/compaction had no effect on leaf P, K and Ca. Leaf Mg was highest in the TC plot but was different only from the NT-C plot. Irrigation did not have significant effect on any leaf nutrient concentrations but generally tended to reduce them. At one and two years after field transplanting, tillage/compaction did not have any significant effect on the primary (P); secondary (S), tertiary (T) and quartemary (Q) roots' length and weight but irrigation significantly increased these roots by 2-3-fold. As total (P + S + T + Q) root length increased, leaf area (per leaf) increased.
