Nutrient Harvests : The Essential Yardstick to Transform Crop Nutrition

Keywords: nutrient harvests, combinable crops, nutrient deficiencies, Yield Enhancement Network, grain analysis.

Nutrient harvests – the quantities of nutrients in harvested crop materials (both kg/ha and % biomass) – are proposed here to be the defining metrics of crop nutrient management. This paper reviews how nutrient harvests can be interpreted usefully, and uses evidence from the Yield Enhancement Network (YEN) to gauge how well the fertiliser and farming industries currently optimise provision of all essential nutrients to combinable crops and the value of routinely measuring nutrient harvests on farms.

Critical concentrations in grain could currently be derived for eight of the 12 essential nutrients, and confidence in these is open to improvement. Grain concentrations measured field-by-field suggest that most (~85%) of even the best farm-grown crops suffer one nutrient deficiency and half suffer more than one. Phosphorus (P) is most commonly deficient, but other macro-nutrients and manganese (Mn) are also of common concern. Nitrogen (N) deficiencies cause most economic loss, but N excesses are also costly; the average cost of N errors was £161/ha across all YEN wheat entries (at 2022 prices). Phosphorus deficiencies were estimated to cost another £126/ha on average. Additionally, both imprecision and inaccuracy in current strategies of fertilising to balance crop P and K removals from land cause unnecessary expense of at least £10/ha on average. Measuring harvested nutrients costs less than £10/ha, so far less than the average total cost of these errors.

It is suggested that crop nutrient recoveries from manure and fertiliser applications, are generally worse than is assumed but a review of responses to foliar nutrient sprays indicates the these are also infrequent. It is suggested that the most effective means of achieving the improvements in crop nutrient management in the short timescales currently required should arise through improved appreciation of crop nutrient recoveries, and that this knowledge could be built from routinely monitoring and sharing field-specific nutrient harvest data widely across farms.

The discussion considers why the industry has not previously used its nutrient harvests to assess its performance. No good reason is noted so the paper concludes that nutrient harvests should be recognised as the essential yardstick of crop nutrient management, and that all farms, whether or not they use inorganic fertilisers, would benefit financially and strategically from routinely measuring their nutrient harvests field-by-field. Accurate intelligence of field-scale nutrient additions and harvests would also reveal environmental performance of nutrient management and assist its improvement. An initiative is now in place called ‘Nutri-Check Net’ whereby these assertions can be disseminated and tested across Europe through the next few years.