PLACEMENT OF FERTILISERS FOR POTATOES

Reduction of fertiliser costs

As the potato root explores only 30% of the cultivated area, all the phosphate requirement for the crop should be placed. Phosphate is immobile in the soil, can be readily fixed by the soil and is required early in the crop life cycle for maximum yield and crop benefits.

Application rates can be reduced by 50-100 kgs/ha over broadcast as placed phosphate is more efficiently taken up and crop requirement of a 50 tonne/ha crop is only 50kgs/ha. This saving at todays prices translates to between 30-50 Euros/ha.

Placed phosphate will increase root weight, optimise tuber number, nutrient and water uptake and increase the speed of establishment.

It is most effective to include both nitrogen and trace-elements with the phosphate at placement, which will help to encourage rapid crop emergence, and avoids the need for costly and largely ineffective foliar nutrients. Most nutrients such as calcium and manganese cannot be efficiently applied as broadcast fertilisers due to oxidation in the soil, and are not translocated from the leaf tissue to the developing tuber where they are required if applied as a foliar.

Increased yield and quality

Fertilisers are more than nitrogen, phosphate and potash as a crop will only grow to the nutrient, which is limiting. Any limitation to crop growth will not only reduce yields but also cause crop stress and therefore quality.

Potatoes grow so quickly that soil availability will often not match uptake, particularly during periods of rapid growth leading to internal disorders, reduced yield and crop stress. Therefore, the placement of critical but immobile nutrients close to the seed will create a spoon feeding of these vital nutrients. They will remain available for uptake as the narrow band of placed nutrients will reduce the opportunity for them to be fixed into the soil complex. Recent research has shown the correlation between certain trace and secondary elements and improved quality characteristics:

Calcium: protection against internal rust spot and increase skin strength

Manganese: reduced common scab

Zinc: reduced powdery scab

Sulphur: improve dry matter formation

Boron: reduced internal browning

Copper: catalyst for Manganese uptake, increases strength of skins.

Available fertiliser technology can now provide these vital nutrients in granules so that they can now be placed accurately for improvement in both yield and quality.

Law Fertilisers have developed a granule containing specific ratios of calcium, boron, manganese, copper, zinc and sulphur, which can be blended with a nitrophosphate for accurate placement at planting.

Potash should not be placed at planting as the chlorine in the product may damage the developing seed. Furthermore, as the demand for potash is so high this nutrient needs to be evenly incorporated in the ridge by broadcasting preplanting, preferably pre-plough.potatoes. This will protect soil structure and reduce rates of placement fertilisers to minimise effects of placement on the speed of planting. The requirement for potash is 6kgs/ha per day so the potash granules need to be uniformly distributed in the potato ridge so the root systems can satisfy the plant demand.

Yield increases from phosphate only placement against broadcast varied from 7 to 15% whilst the addition of Law’s Potato Plus showed further increases of 10 to 25%.

A trial using Law’s Potato Plus in Ireland at County Antrim showed a 12% increase in yield with a good skin finish and processing quality.

More detailed work by SAC in Scotland on the benefits of trace elements for the health of the potato showed reductions in scab, black dot and black scurf incidence.

Environmental Effects

The importance of emissions from agriculture being controlled and minimised so as not only to meet EU guidelines on water and air quality but also to minimise wasteage of farm resources can be addressed by the placement of lower amounts of phosphate and ammoniacal sources of nitrogen close to the seed. Losses of nitrates and phosphates to watercourses and nitrates to the atmosphere not only damage the environment and threaten the sustainability of agriculture but also increase the threat of input taxes and controls from the EU.

The changing environment has also lead to new nutrient requirements, the most important being sulphur. The Clean Air Directives from the EU have dramatically reduced sulphates being deposited onto farmland such that all crops require sulphur, and potatoes require sulphur on a 10:1 ratio to nitrogen to ensure all essential amino acids can be manufactured.

Climate change may not only bring more volatile weather patterns and thus crop stresses but also potentially higher yields. Placed phosphates will increase phosphate uptake and therefore create bigger root systems which will explore a greater soil area and thus minimise the risk of nutrient and water uptake being out of balance with plant demand. Imbalances lead to reduced yields and quality defects such as growth cracks, mis-shapes, scabs and internal disorders. The incorporation of trace elements in a placement fertiliser would not only help to prevent nutrient shortage and thus stress but the use of calcium in particular helps to prevent the production of the stress hormone ethylene which encourages early maturity and thus lower yields.

Increasing Consumption

Placing specific fertilisers will increase the evenness of harvested product size and reduce variation across a field, improving the presentation of the product to the consumer. Placed trace elements will help to improve the appearance of potatoes reducing skin blemishes, improving eating quality and taste and improving size, shape and bloom of tubers. The use of placement fertilisers would reduce the cost per tonne of product and therefore increased consumption could result from lower retail prices. Increasing competition from pasta and rice is having an effect on potato consumption in mainland UK, especially in years of above average prices.

Placement may help to raise product quality standards, which would remove speculative low technology growers, creating a more stable grower sector and marketplace.

The opportunity to develop new potato crops such as seed or salad crops would increase potato markets but would require increased sophistication of production techniques. Placement of fertilisers can increase tuber number and reduce skin diseases, which are fundamental requirements of both of these product sectors.

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