18 | 11 | 2017
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Soil Tillage
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Tillage before planting

Preparation of lands for the planting of lucerne should preferably be started during the spring before the expected autumn planting date.

In the case of a cash crop being fitted in beforehand, at least two months must be allowed after harvesting it, before the lucerne is planted, in order to allow complete breakdown of the crop residue.

Lands which have been in use for several seasons must be deep ploughed to break up hardpan areas. The most important considerations when ploughing are to improve root penetration, drainage and aeration of the soil and to reduce soil compaction.

Furthermore, it helps to control weeds, breaks down and works into the soil any harvest residue, and breaks up large clods. Fertilizer can be added at the same time.

Early preparation of lands is recommended if there is a problem with weeds.

It is necessary to work the lands in the spring and then allow them to lie fallow for the summer, then to work them again in late summer and/or before planting in the autumn.

The advantages of soil tillage are temporary, and a heavy rainstorm can undo them.

If the pH of the soil is correct, then a fallow period (spray instead with herbicide) may be considered as an alternative. This may keep input costs under control.

Exposure of the soil stimulates the activity of micro-organisms which use organic material as a food source.

This can result in a poor carbon-oxygen ratio in the soil, which leads to soil compaction.

Another possible disadvantage of soil preparation is the increased costs.

There is the cost of petrol / diesel, as well as maintenance costs due to wear-and-tear on implements.

Moreover, as ploughing leads to structural damage of the soil, so more powerful tractors must be used.

Fertilisation before planting

Liming should be done before sowing.

During tillage and before sowing is the last chance for relatively insoluble fertilizers such as lime to be well mixed into the soil, so that chemical reactions can release nutrient elements for uptake by the plants.

Nutrients that usually need to be supplemented, other than lime, include phosphorus, potassium and sulphur.

  • Lime

Liming is the most important fertility factor for the establishment and maintenance of high-yield, high-quality lucerne. Guidelines for liming must be based on the exchangeable acidity in the soil and not simply on its pH and texture.The advantages of liming for lucerne include the following:

  • Helps production of optimal yield
  • Increases availability of other elements, e.g. phosphorous and manganese
  • Reduces iron and aluminium toxicity
  • Improves establishment of the stand
  • Increases productive lifetime of the stand
  • Nitrogen-fixing bacteria (Rhizobium) are more active
  • Provides calcium and magnesium
  • Improves soil texture and tillage

For maximum yields, the land should be limed to a pH of 6.7 to 6.9. Yield of lucerne drops rapidly in soil of pH less than 6.7. 

Because lime reacts slowly with soil acids, it should be worked in at least 3-12 months, and preferably longer, before lucerne is sown.

The best time to apply lime is directly after the old lucerne stand has been removed, in a typical 4-6 year cycle of crop rotation.

This allows a longer period for the lime to act on the soil, and tillage for the following crops will mix it thoroughly into the soil.

This should bring the pH up to the required level by the time lucerne is re-planted.

The effectiveness of lime is determined by its chemical purity and by the particle size of the source.

The finer the particles, the more effective the action and the more quickly the desired pH will be reached.

To obtain the same change in pH with coarser lime would require its being spread a longer period before planting time as well as in greater quantities.It is, however, cheaper.

Also, coarser lime would not need to be applied as often as finergrained lime.



 

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