Effects of seedbed properties on crop emergence: 2. Effects of aggregate size, sowing depth and initial water content under dry weather conditions

摘要

Rapid and uniform crop establishment is a prerequisite for efficient crop production and minimal environmental impact. Extensive experiments were carried out in shallow plastic boxes placed in the field directly on the ground for studies of the effects of seedbed properties on emergence of small-grain cereal crops in a cool, temperate climate. This paper presents studies of the seedbed as a protective layer against evaporation and the requirements for good emergence under dry weather conditions. Without rainfall after sowing, nearly complete emergence of barley (Hordeum vulgare L.) was obtained, when rapidly germinating seed was placed on a moderately compacted basal layer containing at least 5% (w/w) plant-available water and covered by a 4 cm deep surface layer consisting of aggregates <5 mm. This applied even when initial water content in the surface layer was below the wilting point and potential evaporation was high. If the soil at 4 cm depth is drier or if a sufficiently fine seedbed cannot be obtained, then seedbed and sowing depth should be somewhat greater, and if the soil is wetter, then the depth may be smaller. There were only small differences in emergence between surface layers consisting of aggregates <2 mm, 2-4 mm or 2-5 mm, or dominated by these aggregate fractions, but when the surface layer consisted of coarser aggregates, emergence was usually much lower. Determinations of water losses from the soil during the experimental period showed that the differences in emergence were caused by differences in efficiency of the seedbed to control evaporation. The results indicate that, in an initially wet soil, it is always possible to find a time and method for seedbed preparation and sowing that lead to good emergence of small-grain cereal crops, even with a lengthy period without rainfall after sowing.