By Doug McClymont
The fortunate thing about winter tillage is that there is irrigation available to help with the situation. Winter crops in Zimbabwe have to be grown under irrigation so with this asset available one has total freedom to choose the method of tillage. The larger field crops grown include wheat and barley while there are smaller areas of potatoes and onions. Having larger seeds, wheat and barley do not have to have as fine a seedbed as onions or potatoes. The vital issue pertaining to winter tillage in Zimbabwe at the moment relates to one thing and one thing only… diesel! For various reasons it is essential to prepare the soil and plant the winter crop WITH AS LITTLE DIESEL AS POSSIBLE. How this is done depends on three things:
1. What was the previous crop?
2. What sort of tilth do I need?
3. What do I have to do to ensure successful establishment of the winter crop?
PREVIOUS CROP
Handling the residue of the previous crop is important when choosing the subsequent operations. For conservation tillage one needs to preserve as much organic matter as possible for many reasons. With larger seeds like wheat and barley this is not a problem and with large crops like maize the residue provides a good mulch cover. The photo above shows a large amount of maize stover left over. This had wheat broadcast over it to give the following results and a crop of 9 tonnes/ha. Unfortunately with small seeded crops like onions and for potatoes this residue is far too much and separate means are required to enable the tillage implement to give the right tilth.
TYPE OF TILTH
As shown above larger seeds do not need a specialised tilth provided there is some mulch available. For the fine seeded crops like onions soil/seed contact is all important and precision planting is required whether by machine or planted setts. For potatoes the soil must be in a form that enables the production of a suitable ridge. In these cases plant residues are a hindrance, and all though (shock … horror) it goes against conservation ideals I would burn off the residue under present circumstances. Dealing with the residue will need extra diesel!
OPTIONS AVAILABLE UNDER DIESEL CONSTRAINTS
We have seen seed broadcast into flattened residue but there may be problems that have to be rectified before proceeding. One needs to test the soil when wet and I use a cut down Manipular clip (thanks to Brown Engineering) to probe the soil to determine if there is a hard pan. A typical example is shown below.
To break this one has to rip. Normally this will bring up big clods and these must be bashed right away if you do not want bricks. In Zimbabwe I would never rip without trailing at least a Cambridge roller behind to get an even result. After ripping one could then disc harrow (Rome) to get a good tilth. However in the case of onions this is not good enough and a rotavator should be used. During the tillage operations one MUST ensure the correct soil moisture, so judicious use of irrigation water has to be part of the equation. Add to this the broadcasting of 500 kg/ha gypsum as a soil softener before planting and one also guarantees that extra sulphur, so necessary for falling numbers and gluten in wheat, malting quality in barley, keeping quality in potatoes and onions and especially the taste in onions.
If one wishes to drill wheat or barley then trash freeways are essential in large plant residues.
So to summarise for minimal diesel use:
1. Rip and roll if you have a plough/disc pan
2. For big seeds flatten the previous residue if the combine has not already done so (NB that is why an efficient trash spreader on the combine is so important)
3. Broadcast the seed or drill with trash freeway
4. For small seeds burn off the previous large residue if you can, flail mow and disc in crops with minimal residues
5. Rotavate surface for onions, cross disc and ridge for
potatoes
6. Remember to use irrigation to keep soil at correct
moisture for tillage
7. Record your diesel usage per ha.