Now is the time to pay attention to your soils and fertility Print
This time of the year it is important to prepare your fertility and soil improvement programs. An effective way of doing this is by preparing a fertilization plan. Advisors can help you determine what your additions of organic materials and nutrients should be.  By comparing crop requirements with legal nutrient levels, the right sources can be chosen for the supply of organic matter and fertilizers.

Crop rotation is important for the biodiversity of the soil, especially at operations with monocultures such as Buxus, too often this is neglected.  Green manure crops are an option in such situations.

Soil quality can be greatly improved by choosing deep rooting green manure crops. This will help to break up hardpans and improve aeration of the soil.  Especially useful are oil seed radish and Sudan grass as their roots can penetrate deeply.

Green manure crops will greatly reduce clodding of clay soils. This is especially important for the culture of shade trees, which are often harvested under adverse conditions.

These plants can also contribute significantly to the amount of organic matter in the soil. Organic matter is important in soils as they feed micro-organisms which bind and retain nutrients.

For example, light sandy soils require an annual addition of 1,200 to 2,800 kg of effective organic matter per hectare to make up for decomposition.  Green manure crops deliver fresh organic matter to the soil which is especially important for micro-organisms in the soil.  However make sure that the addition of organic matter is done in a balanced manner.  Green manures are an addition to animal manures and compost, not a replacement.

Nematodes

Green manures can have a big influence on nematode control.  Basamid (dazomet) as a nematode control agent will no longer be available (in the Netherlands) after June 2009 and other chemical control methods are also limited in availability.
 
The choice of green manure crop will be guided by the presence and pressure of certain species of nematodes in the field.  Soil samples need to be taken to ascertain the genera and species as well as the pathogenic pressure of the nematode population.  To reduce the risk, make sure that the sample is tested with an incubation period.

You can make use of the characteristics of green manure crops to reduce nematode pressure. Tagetes (marigold) works well against Pratylenchus (root lesion nematode), but promotes the multiplication of Trichodorus.  Since Trichodorus is known to spread viruses in perennials, this strategy can be risky.

Oil seed radish works exactly the opposite way. Pratylenchus and Meloidogyne (root knot nematode) multiply in its presence.  The new ‘Doublet’ race is however active against Meloidegyne.  If Pratylenchus is not present in the soil, this green manure crop can be used to effectively reduce nematode pressure.

Sudan grass (Sorghum) has had mixed results in the field.  Pratylenchus penetrans is supposed to be destroyed as the crop is worked into the soil.  Trials so far have shown mixed results.  Sometimes the presence of P. pentrans actually increases.

source: Kees Pastoor
DLV Plant, Boskoop, The Netherlands
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