Calcium - Carrots and Potatoes
POTATO AND CARROT NUTRITION
Nutrition of the carrot and other vegetable crops is coming under increasing scrutiny as the number of pesticides available to control pests and diseases is reducing. However the supermarket still requires uniform, clean vegetables for their shelves.
By ensuring crop nutrition is good we can increase the plants resistance to both pests and diseases, thus increasing pack out percentage whilst still fulfilling all other requirements.
Calcium deficiency in carrots is implicated in a number of diseases such as Cavity Spot, Sclerotinia and shading of the skin etc.
Many carrots are grown on sandy soils which are subject to nutrient leaching .Growers are aware that high levels of N will encourage top growth but this is at the expense of the roots. Vigorously growing plants with plenty of foliage are more likely to suffer calcium and boron problems than plants which are less vigorous and grow steadily throughout the season.
Calcium is very immobile within the plant €“ it moves in the xylem with the water, hence crops with vigorous tops which are transpiring actively will transport virtually all of the calcium absorbed by the basal roots into the leaves and away from the roots. Calcium and boron applied to the leaves will not readily move either from old leaves to new nor from leaves down to roots.
Therefore in order to increase the levels of calcium in the roots it is important to place calcium into the actual root zone. Applying Calcium and boron to the soil allows the plant a steady uptake throughout the growing season.
Seedlings are totally reliant on nutrients stored in the seed until their roots are able to absorb nutrients. Applying urea nitrogen and calcium in the seed zone allows the developing plant to rapidly absorb the nutrients required for strong healthy plant growth resulting in more even growth and better shaped carrots
Boron is the key element in several plant growth processes affecting quality..
Boron is also relatively immobile within the plant but helps to bind calcium into cell walls (Clarkson & Hanson), thus improving stress and disease resistance and skin finish.
Plants with a good calcium status require more boron.
High rates of P and K such as applied to potatoes may accentuate boron deficiencies.
Boron can speed the flow of sugars produced by photosynthesis and is essential for providing sugars for root growth.
Boron affects the nitrate reductase enzyme and boron deficiency interferes with both nitrogen and carbohydrate metabolism.. Boron also affects phosphorus metabolism.
Due to its immobility Boron must be continually supplied to the plant. Foliar applications of calcium and boron at frequent intervals ensures strong healthy leaf growth, helps the plant to utilise nitrogen and aids movement of sugars and carbohydrates to the tubers. Supplying the leaf requirements for calcium in this way can also help the plant to divert more calcium to the tubers.
Work at SAC showed that there was a correlation between soil zinc levels and powdery scab. Ensuring that plant zinc levels are good will increase resistance to many diseases including blight but it also appears that zinc, and other heavy metals such as manganese, can poison the zoospores of the fungus.
Sulphur has also been reported to reduce levels of scab in potatoes. There are several aspects to this since sulphur may be acting as a nutrient in its own right, it can also have fungicidal effects, and by acidifying soil as it oxidises it makes other nutrients such as manganese, copper and zinc more available to the crop.
Maintaining a good nutrient status within the plant will enhance resistance to disease but the fungi which cause both Common Scab and Powdery scab seem to be susceptible to increased levels of heavy metals.from a report by StuartWaleSAC.
40k-50k/ha Potato Mix applied into the ridge at planting
1-1.5l/ha Set applied with each blight spray.
This supplies the developing tubers with calcium and other nutrients leading to a more even set and hence tuber size and better skin finish. The foliar sprays increase the Ca in the leaves thus increasing the plants resistance to stress and diseases, and reducing the calcium pull away from the tubers.
Potato haulm remains greener and healthier throughout the season. Skin finishis improved and internal defects reduced. ( see trial results)
Where internal rust spot is a problem it is far better to use both methods of application rather than concentrating on the foliar applications.