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 (di agnosis) or predict its occurrence at a later stage of growth (prognosis). Its use is based on the presumption that the plant nutrient status will eit her be constant with plant age or follow a predictable pattern of change ov er time after sampling. However, a period of deficiency during plant growth followed by the recovery of nutrient uptake to satisfactory rates may caus e an irreversible impairment of growth which plant analysis fails to diagno se or predict. Several cases are considered, each involving a temporary def iciency of, or interruption to nutrient supply. Such cases generally involv e but are not restricted to micronutrient deficiency. For example, B defici ency 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 ana lysis after emergence does not. Similarly, Zn deficiency impairs early grow th of transplanted oilseed rape (Brassica napus L.) seedlings and eventuall y depresses seed yield. However, leaf analysis during crop growth fails to diagnose a Zn deficiency. Finally, temporary B deficiency induced by low va pour pressure deficit or low soil water especially during reproductive deve lopment may depress yield markedly but remain difficult to diagnose by plan t analysis. Strategies for diagnosing and predicting such temporary deficie ncies are discussed including the measurement of environmental parameters s uch as pan evaporation or rainfall and their inclusion in multi-variate reg ression models of plant response to nutrients.