Horticulture notes August 2008
FIELD CROPS
Mustard – a natural alternative
As fertiliser and chemical prices rise ever higher, growers would welcome any cheaper alternatives for nutrition and weed control. My colleague in Crops and Horticulture Branch, Teresa Maguire, has been leading a project to investigate how Caliente mustard (Brassica juncea and Sinapsis alba) might be helpful in these roles. Caliente mustard belongs to the Brassica family and can be used as a green manure; it also has the added advantage of acting as a soil fumigant against weed seeds and soil diseases.
The project has been running at Greenmount Campus since 2006, with assessments at some grower sites in 2007. The procedure for using mustard in this way is quite straightforward:
- Soil is tested to ensure pH and base fertility is suitable.
- Seed can be sown in spring, summer or autumn. An April sowing takes as little as 10 weeks to reach flowering.
- The crop is cut down, chopped and ploughed in at the flowering stage. It should be ploughed in quickly after cutting, to prevent nutrients escaping into the atmosphere.
Results from evaluations carried out by CAFRE since 2006 in both conventional and organic vegetable fields have shown that this approach can suppress weed germination. On average, two weeks after ploughing in the mustard crop weed germination was reduced by 42 percent compared with the untreated parts of the field. Weed germination was still reduced by at least 22 percent seven weeks later.
Table 1: Percentage weed reduction after incorporation from a nine week summer mustard crop
| Treatments | % weed reduction two weeks after incorporation |
% weed reduction seven weeks after incorporation |
|---|---|---|
| Conventional grower 1 | 41% | 22% |
| Conventional grower 2 | 43% | 26% |
| Organic grower | 43% | 22% |
Teresa explained the potential of this green manure to growers of field crops. “While this product and others in the same family are still in development, we are starting to see benefits in terms of reduced herbicide inputs. We know that mustard releases nitrogen slowly so we are looking at how this impacts soil nutrition over a number of seasons. We are also working with AFBI to see if mustard might suppress nematode pests in soil.”
Further trials are being carried out in 2008 to evaluate the use of Caliente mustard and other potential crops in the field situation, within different rotations and seasons.
TOP FRUIT
Summer nutrition
This season has seen a number of orchards showing minor nutritional imbalances, particularly for the nutrients magnesium, potassium and manganese, which aren’t part of most sown fertilisers. This is where foliar nutrition comes into its own, supporting the crop through periods of possible stress.
The substantial set for ‘Bramley’ with our prolonged dry weather in the late spring/ early summer has put significant demands on your trees. Remember too, that a heavy crop and late fruit swell can reduce the levels of calcium and phosphorus in storage. It is vital to apply the full rate of these two nutrients to minimise the risk of bitter pit and low temperature breakdown respectively.
If you wish to check how successful your feeding is a leaf analysis service is available through AFBI, Loughgall. Growers can take samples into AFBI, Loughgall, on any day between 11 and 15 August. The analysis costs £17.18 including VAT and results will be posted out directly to you. You can then contact me to discuss any interpretation you might need. Growers will soon receive a letter explaining this service and giving information on fruit analysis for this autumn.
The mustard crop (left) and the field after incorporation (right) in an organic field situation