Temporary nutrient deficiency - A difficult case for diagnosis and prognosis by plant analysis

Plant analysis aims to either detect deficiency at the time of sampling (diagnosis) or predict its occurrence at a later stage of growth (prognosis). Its use is based on the presumption that the plant nutrient status will either be constant with plant age or follow a predictable pattern of change over time after sampling. However, a period of deficiency during plant growth followed by the recovery of nutrient uptake to satisfactory rates may cause an irreversible impairment of growth which plant analysis fails to diagnose or predict. Several cases are considered, each involving a temporary deficiency of, or interruption to nutrient supply. Such cases generally involve but are not restricted to micronutrient deficiency. For example, B deficiency impairs early seedling growth when seeds low in B are planted, even on B fertilised soils. Low B concentration in seeds diagnoses the subsequent impairment of seed germination or seedling establishment: however, leaf analysis after emergence does not. Similarly, Zn deficiency impairs early growth of transplanted oilseed rape (Brassica napus L.) seedlings and eventually depresses seed yield. However, leaf analysis during crop growth fails to diagnose a Zn deficiency. Finally, temporary B deficiency induced by low vapour pressure deficit or low soil water especially during reproductive development may depress yield markedly but remain difficult to diagnose by plant analysis. Strategies for diagnosing and predicting such temporary deficiencies are discussed including the measurement of environmental parameters such as pan evaporation or rainfall and their inclusion in multi-variate regression models of plant response to nutrients.