Agroforestry on alkali soils: Effect on some management practices on initial growth,biomass accumulation and chemical composition of selected tree species

This field study started in July 1982 on a typical alkali soil (Aquic Natrustalf, ESP 99.7) examined the growth responses to some management practices in a unified system planned to establish agroforestry. The planting of 3 salt tolerant tree species with two methods: on flat natural surface (FSPB) without rainwater conservation and on ridges (0.6 m high, 1.5 m at top and 2.5 m at base) having parallel trenches of the same section to store 300 mm of monsoon rainwater; constituted the main plot treatments. The tree planting with and without forage grassDiplachne fusca linn. in the inter-row space and planting in shallow (15 × 60 cm) and deep (15 × 180 cm to cross hard pan) augerholes filled with amendment treated soil (2 kg gypsum, 8 kg FYM, 50 g N, 10 g zinc sulphate and original soil) formed the sub and sub-plot treatments replicated 4 times in a split-split plot design.The mean plant height ofEucalyptus tereticornis smith;Acacia nilotica L; andParkinsonia aculeata L. in 2 years period was 273 and 328, 240 and 240 and 211 and 199 cm respectively with and without rainwater conservation. The corresponding height of the 3 tree species was 314 and 287, 250 and 231 and 207 and 203 cm with and without grass in the inter-row space. Similarly the plant height was 247 and 354, 182 and 298, 172 and 238 in shallow and deep augerholes respectively. The tree height and basal diameter differences with and without rainwater conservation and grass growth remained non-significant but deep augerhole planting was markedly superior to the shallow augerhole planting. The 2 year biomass accumulation also followed the same trend. The grass competed with trees for moisture during hot dry summer months and increased plant mortality particularly in the shallow augerholes and more so on ridges. The plant roots, essentially, remained confined to the amended soil of the augerholes in FSPB but proliferated in the loose soil of ridges or grass and submergence ameliorated surface soil of trenches.Acacia nilotica accumulated low sodium and had the lowest Na:Ca and Na:K ratio. It was found more promising than eucalyptus and parkinsonia as it experienced low mortality and had better chemical constitution to tolerate adverse alkali soil environment. The rainwater conservation system needed further evaluation before drawing final conclusions.