Såbäddar för vårstråsäd

Poor crop emergence causes significant economic losses to Swedish agricul ture, the most common reasans being drought, crusting, and too deep sowing. In a sampling investigation embracing 300 spring-sown fields distributed all over the country, basic data concerning the properties of the seedbed we re collected. The following praperties were studied: The depth of the seedbed (~ the harrowing depth), the roughness of its surface and battom, the moisture conditions, the soi1 temperature , the aggregate size distribution I the seed placement, and the resulting crop emergence. Particle size distribution and moisture content (by weight) at the matric tensions of l., 1.0 and 1.50 m water column (pF 2, 3 and 4.2 respectively) were determined for the so1.1 from each of the 300 sampling sites. Using multiple regression analysis the influence of the soil composition on the moisture content at the three tensions mentioned was studied. The sampling was done immediately after sowing. The seedbed, normally being 5-6 cm deep, was divided into three sublayers. In each of these / and in a 2 cm thick layer be1ow the seedbed bottom/ the moisture content was determined. The content of plant available water in the who1e seedbed had a maximum, about 5 mm, in soils with about 10 % clay. For soi1s with a clay content above 30 % it: was about 0 mm independent of the clay content. In the 2 cm thick layer below the seedbed bottom there was normal1y 3-4 mm of plant available water. Soil material from each sublayer was sieved into three aggregate fractions, < 2 , 2-5, and > 5 mm, and the aggregate size distribution as a function of the depth and of clay content of the soil was analyzed the relative number of seeds in the three sublayers was determined, and the median sowing depth calcu1ated crop emergence on the sampled sites 2-3 weeks after sowing was estimated and reported by the farmers. Based on the results of the investigation a simple model for suitable sowing depth for cerea1s on different soils under Swedish weather conditions was worked out.