Rabindra K. Misra

Establishing woody perennials on hostile soils in arid and semi-arid regions – A review

Background and aimsWoody perennials can be difficult to establish on harsh soils in arid and semi-arid regions. Historically, technological advances have focussed on methods to improve transplanting and direct-seeding but the available information on these advances remains fragmented and the edaphic factors have been largely ignored. This review explores the literature on plant establishment and identifies soil properties that limit plant response in harsh environments.ConclusionsWe reveal that some woody perennials are particularly well-adapted to dry conditions and can also help reclaim degraded landscapes. Furthermore, the environmental and phenological factors that limit the success of direct seeding are well understood but the edaphic factors are not. For example, seedbed preparation and subsoil amelioration before seeding have not been evaluated in dry regions. Seed-priming and seed-placement are also poorly understood, as is the tolerance of woody perennials to different salt types in waterlogged soils of extreme pH and high soil strength. The reason why woody perennials can penetrate strong, hard soils is not obvious from the literature. They apparently cannot exert root growth pressures of the same magnitude as domesticated plants, so they must be able to exploit soil biopores and cracks more efficiently. Other gaps in our understanding of the soil factors that limit woody perennial establishment on hostile soils are identified.

Comparison of the penetration of primary and lateral roots of pea and different tree seedlings growing in hard soils

Establishment and survival of tree seedlings in hard soils depends on production of deep root systems. This study evaluated the primary and lateral roots of an annual crop and several tree species growing in soils of varying strength. We grew peas and acacias by direct seeding, plus three eucalypts by direct seeding and transplanting, and measured various root characteristics. At all levels of soil compaction, the primary roots of acacia were thicker and they elongated faster than did those of the eucalypts. However, lateral roots of transplanted eucalypts elongated faster than their primary roots, and the rate of root elongation was negatively correlated with soil penetration resistance, especially for Eucalyptus camaldulensis. The primary root diameter of all plants increased with increasing penetration resistance, but acacia roots continued to elongate faster than pea roots. Pea plants produced most of their roots in the top 5 cm, whereas tree roots were more uniformly distributed with depth. Although not statistically significant at P = 0.05, the relative rate of root elongation in very hard soil correlated modestly (P = 0.11) with the maximum root growth pressure of four tree species. These variations in root growth behaviour can be related to the intrinsic variability of root characteristics for each plant species and the natural abundance of each species in different environments.