Question: About a year ago, rising fuel prices led us to switch our maize planting from conventional tillage methods to minimum till. Our deep, sandy soils, (about 2 m) range in colour from yellow to red, and the water table is 60 cm below the surface. We sprayed off the lands before planting, and put the fertiliser on at the recommended rate. Our plant population was from 28 000 to 30 000 plants/ha. Now, we have a problem; the maize is not growing and is actually beginning to dry out, despite the fact that the soil is moist. Our neighbour’s conventionally tilled and planted maize looks good. What’s the problem with ours?
Dig down and look at the roots
Maize on lands with this kind of water table should not have a problem, unless the roots can’t reach the water. The growth of the plant, above the surface, depends on the capacity of the roots, below the surface.
The weak growth, and your observation that the maize is beginning to die, is most likely because of soil compaction which has created an impermeable barrier that stops the roots from getting to water.
These soils have been formed by wind deposits of sand over millions of years, and they have a tendency to compact and form a shield. After a heavy rain, when the soil is saturated, the combined weight of soil and water causes downward settling, or consolidation, of the soil. As the water is squeezed out, the soil particles, ranging in size from 2 mm to 0.05 mm, integrate fairly easily and form a compaction layer.
The fact that the plant roots cannot get to the moisture, below the surface, points to compaction. When you switched to minimum till, you probably stopped ripping, a practice that removes compaction layers. This tends to happen with minimum till.
You will have to rip along with the minimum till, or you will suffer serious harvest losses. There are advocates of minimum till who will differ from me on this point, but they do not necessarily know these soil types. Dig down and look at your root development – the roots should illustrate the problem quite clearly.
- Dr Eduard Hoffman, soil scientist.