The increased moisture is a result of the residue layer that reduces evaporation from the soil. As well, the standing stubble contributes to higher soil moisture by trapping snow and reducing wind speed for reduced evaporation. In the spring, the soil is warmest near the surface, which is very important for direct seeding. Table 1 shows that much of the heat advantage tillage has when seeding at 5 cm depth can be offset by seeding shallower when direct seeding. The higher near-surface soil moisture levels under direct seeding are critical for making shallow seeding viable.
Further research is needed to determine optimum levels of residue for direct seeded soils.
As well, slope characteristics, organic matter content and soil texture affect soil temperature. Soils higher up on slopes are usually drier than soils in lower areas, and therefore usually warm faster. Similarly, sandy soils and soils low in organic matter tend to hold less moisture and so may warm faster than clay soils and soils higher in organic matter. Germination and seedling growth are variable and slow at low soil temperatures. As tem- perature increases, germination and emergence become faster and more uniform.