A review of the non-NPKS nutrient requirements of UK cereals and oilseed rape

This review investigates the importance of non-NPKS nutrients within cereal and oilseed rape production systems. The review considers crop requirements, sources of nutrients, occurrence and diagnosis of deficiencies, strategies for avoiding/rectifying deficiencies, and knowledge gaps.

Crop requirements. The function of each nutrient for the plant is summarised and, where possible, data on crop uptake and offtake amounts quantified. Up to date information for maximum crop uptake and crop offtake could not be found for all nutrients (e.g. Molybdenum) and further work is required to rectify these knowledge gaps.

Sources of nutrients. The concentration range of each nutrient in agricultural soils is summarised. Factors and soil processes which affect the availability of nutrients for plant uptake are described. Sources of each nutrient are summarised, and where possible quantified, including from additions such as manures, organic residues and atmospheric deposition. Information about the nutrients that could be supplied in manures could not be found for all nutrients (e.g. boron and manganese). Without additions of manures, organic residues or fertiliser sources, crop offtake may exceed inputs for copper, zinc and magnesium, and possibly manganese.

Incidence of deficiency. More than 400 crop response experiments were analysed. These included information in published literature and unpublished data for soils and climates which were either UK or relevant to UK conditions. All experiments had replicated treatments and were statistically analysed. Statistically significant yield responses were found for five out of 48 boron experiments on oilseed rape (three out of 19 in the UK), none out of 33 boron experiments on cereals (13 of which were in the UK), 93 out of 197 copper experiments on cereals (61 out of 114 in the UK), 33 out of 111 manganese experiments on cereals (28 out of 80 in the UK), two out of 14 magnesium experiments (two out of 13 in the UK), four out of eight molybdenum experiments on oilseed rape in the UK, and 11 out of 72 cereal experiments on zinc (six out of 36 in the UK). A survey of agronomists indicated that the most prevalent deficiencies were, for cereals: magnesium, manganese, copper and zinc; and for oilseed rape: magnesium, boron, manganese and molybdenum.

Diagnostic methods. Details and guidance for soil and tissue tests from different laboratories and organisations were compared. This indicated reasonable, but not complete, agreement between the analytical methods used and guidance on thresholds. Confidence in soil testing for non-NPKS nutrients could be improved by standardisation of testing methods. Research is also required to clarify the effects of factors such as soil type and pH on nutrient availability and the thresholds.

Treatment strategies. The most effective treatments for correcting deficiencies are summarised.

Economic evaluation. The yield response required to cover the cost of non-NPKS fertilisers was generally less than 0.1 t/ha which is less than the smallest statistically significant difference that can be detected using conventional experimental designs (0.3 to 0.5 t/ha). It is therefore important that experimental methods are developed that will allow smaller differences in crop response to be reliably detected.