Of interest to growers: Choosing the right green manure crops Print
Nursery growers are well aware that good cultural practices require the re-conditioning of land after the harvest of a crop.  The process should start with a soil test to determine which nutrients have been depleted and need to be supplemented.  Especially if no crop is planted for a year, the planting of a green manure crop is an important consideration.  

Green manure crops can dramatically improve the structure of the soil, its aeration and water holding capacity, suppress weeds and nematodes and in some cases attract natural predators.  Before planting a green manure crop however, it is important to conduct a nematode test, as your choice of green manure crops will, in part, be determined by the type of parasitic nematodes present in the soil.

It is a good practice to spread and incorporate organic matter prior to seeding the green manure crop.  This could be stable manures, bio solids or composts.  Deep cultivation prior to seeding can also remove compaction layers and allow for better water percolation.

Choice of green manure crop

Marigolds (Tagetes) can be seeded when the risk of night frosts has passed.  This selection is well known for its ability to combat the presence of the nematode ‘Pratylenchus penetrans’.  The most used varieties are ‘Groundcontrol’, ‘Singlegold’ and ‘Sparkymix’ as they contain thiophene, a compound released by the roots of the plants that, when attacked by nematodes, causes the nematodes to die.  To achieve proper nematode control when using Tagetes  it is important that good weed control takes place prior to seeding.  The crop also needs to grow for a minimum of 100 days to be effective.  Since the seed is killed by frost, this plant will not re-appear in next year’s crop.

Yellow mustard can be seeded anytime from mid-May to late September. This green manure crop is very fast growing, covering the field quickly and therefore an excellent weed suppressant.  The seeds of this crop are also killed by frost. Yellow mustard does not have any effect on nematodes.

Oilseed radish (Raphanus sativus or R. sativus var. Oleiferus) is a well-known green manure crop because of its rapid growth and good weed suppressant qualities. It can be seeded from mid-May until late August.  This green manure crop does not have any effect on ‘Pratylenchus penetrans’ nematodes.  The seed of oilseed radish is not killed by frost, so it is important not to let the crop go to seed before it is incorporated into the ground.

Sudan grass (Sorghum) can be planted from mid-May until late July.  It forms a big and heavy crop that can be used for so called ‘biological fumigation’. The plants are worked into the soil and, during the decomposition of the crop, hydrogen cyanide gas is released. This kills everything living that it comes in contact with, the most important of which are plant parasitic nematodes.

Avena strigosa (Bristle Barley or Astrigosa) can be planted from mid-April till September, but requires heat to grow properly.  Up to 70 percent of all ‘Pratylenchus penetrans’ are killed as the result of growing this crop.  Because of its rapid growth, this plant is also a very good weed suppressant.  It does not re-appear in subsequent crops.  For mild infestations of nematodes, this plant is a good economical alternative to marigolds.

Source:  De Boomkwekerij     
 

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