Agricultural Sciences: Techniques and Innovations Vol. 12

Nutrient disorders in perennial woody crops and amenity trees are frequently refractory to soil fertilisation because calcareous or alkaline substrates immobilise applied micronutrients, and to foliar sprays because several elements move poorly once deposited on the leaf surface. Stem injection, the direct introduction of solutions into functional xylem through a port in the trunk, has been proposed for more than nine decades as a way of bypassing both bottlenecks. Interest has intensified as injection hardware developed for pesticide and antibacterial delivery has become commercially available, yet the nutritional application has never been subjected to the same critical scrutiny as the plant-protection application. This review examines the physiological basis, delivery technology, agronomic evidence and physiological cost of stem injection used specifically for nutrient delivery. Literature was identified through structured searching of scholarly bibliographic indexes accessible during preparation, supplemented by backward citation searching, and appraised for design adequacy, controls, measurement validity and generalisability rather than scored with a formal instrument. Four conclusions emerge with differing degrees of confidence. Correction of iron deficiency chlorosis by injected ferrous sulphate is the best-supported application, replicated across several genera and reported to persist for more than one season, although most trials are small, short and conducted on severely chlorotic trees. Evidence for zinc, manganese and boron is thinner, is often confounded with co-injected fungicidal compounds, and includes documented failures to reach critical leaf concentrations. Macronutrient delivery is constrained by a mass-balance problem that no reported injection protocol resolves, and the single well-documented magnesium trial found the approach ineffective. Injection ports impose a reproducible wound whose consequences depend on host compartmentalisation capacity, dose and pressure, and are rarely followed for long enough to quantify cumulative cost under repeated annual use. The dominant unresolved question is not whether injected nutrients enter the tree, which is well established, but whether the delivered dose reaches deficient tissue in a spatially uniform and physiologically meaningful quantity at acceptable cost to the stem.