Uptake, not Off take, is Key to Optimum Fertiliser Use

Total demand by a crop of the main nutrients is far in excess of the off take of these nutrients. Yet off take remains the basis of most fertiliser recommendations. Such an approach is simply out of date, particularly when considering today's yield and quality targets. It should be uptake that drives recommendations, together with precise application of each nutrient component, when most required, advises Law Fertilisers.

"Where fertiliser applied is short of crop demand, the plant satisfies its requirements by using soil reserves which are subsequently replenished after the crop is harvested. If short term demand is not met, then the crop will be under stress. This affects both quality such as skin finish in potatoes and yield such as the seed count in oilseed rape and ear size in wheat. If the key nutrient is available for uptake at the appropriate time, then maximum yield is more likely to be achieved," says Mark Law, Managing Director of Law Fertilisers Ltd.

Mark explains that during the early stages of growth when root development is dominant, phosphate is the most important nutrient, with the plant requirement for phosphate being greater than potash. "Therefore it is important to apply soluble phosphate in the seedbed and, where possible, with precision seeded vegetables close to the seed or tuber with appropriate equipment."

"In most plants the total potassium content is larger than that of any other plant nutrient, even nitrogen, with uptake several times greater than both offtake and national recommendation levels. If drought conditions prevail, foliar potash will give a greater yield response than foliar nitrogen. Peak demand occurs at flowering for cereal and oilseed rape crops, with rates of uptake being between 5-10 kg/ha/day for root crops and oilseed crops."

According to Mark, it is essential that the plant has access to these daily amounts.

"The typical uptake of potassium by a high yielding wheat crop is between 330 and 350 kgs/hectare, for oilseed rape 350-400 kgs/ha and for sugar beet 400-450 kgs/ha of K20. When these values are compared to the current standard recommendation, it is obvious why average yields have been relatively static over a prolonged period," he says.

Mark predicts that improved agrochemical and genetic technology together with elevated levels of atmospheric CO² and sunlight could lead to an increase in the maximum yield potential of all major crops. "Law Fertilisers consider the uptake of every key nutrient, rather than the offtake of P, K and Mg, and its correct and timely placement. Such a strategy is the only way to achieve maximum yields."

Laws Fertilisers also point out that micronutrients such as copper may be needed in quantities as little as a few grammes per hectare, but adequate supplies are essential if crop yield and quality do not suffer. "Copper is as important a trace element as manganese in cereals, but, because of its wide-ranging roles within the plant, deficiency is rarely seen apart from loss of yield. In extreme deficiency in cereals the young leaves are pale green and develop white tips and exaggerated twisting," says Mr. Law.

Mark advises that where there is manganese deficiency, there is also likely to be copper deficiency. This covers situations of high pH soils, sandy or peaty soil textures or high phosphate levels where the trace elements are unavailable, or other soils where the copper level is low or has been depleted.

"Soil or plant sampling can help identify risks. Foliar feeds need to be applied from early spring growth and continued through to T3 growth stages. Alternatively, unlike manganese, soil treatments can correct a deficiency for several years."

Although the copper price has seen a significant increase due to Asian industrialisation, the targeted use of soluble copper granular compounds will be beneficial for many cereal growers, Mark notes.