The creation of longitudinal cracks in shrinking soils to enhance seedling emergence. Part II. The effect of surface micro‐relief

Abstract

AbstractCrusting and hardsetting phenomena are major problems in the emergence of delicate seedlings through weak structured soils. When a hard layer develops on the surface, it can retard seedling emergence and the trapped seedlings may perish unless the hard layer is broken or weakened. The development of natural desiccation cracks on the soil surface creates a route by which seedlings can emerge. The work conducted by the same authors suggested that the compaction of soil strips over the seed rows creates longitudinal cracks along the planting lines to improve seedling emergence. This study is an attempt to develop an alternative method to create the linear cracks using the effect of surface micro‐relief. Preliminary experiments showed that the creation of small furrows (50 mm deep) on the soil surface caused the appearance of cracks mainly at the bottom of the furrows. Monitoring the movement of aggregates during drainage, where small depressions are formed on the soil surface, revealed that the aggregates on either side of the turning point of the depression move in opposite directions as a result of the greater water tension developed in the ridges causing development of cracks at the turning point. Laboratory experiments indicated that the radius of curvature at the turning point of the depression, the spacing between depressions and the shape of ridges either side of the depressions are key factors influencing crack development at the bottom of depressions. A field experiment in semi‐arid central Iran confirmed the feasibility of the technique by the use of a backward raked shaper to develop small ridge and furrows on the surface of the seedbed which resulted in the creation of longitudinal cracks in the furrow bottoms, coincident with the seed row. An outline design of a press wheel is given.