Causes and implications of potassium variability in orchards (optimizing potassium management in almond)

M. Germani, P.H. Brown
In almonds, K-fertilization represents a significant expense for the grower: the K off-take in an average crop of 300-400 kg K ha represents >$100,000 fertilizer cost at 2022 prices. Several field surveys of visually uniform orchards find K as the most variable macronutrient element, varying markedly between samples, dates and space. In the absence of other methodologies, growers largely base their K fertilization decision on leaf analysis, which is highly variable and difficult to interpret. As a consequence of this variability and sampling and interpretation uncertainty, and to avoid the risk of K deficiency in high-value crops, growers routinely apply excess K and adopt leaf nutrient guidelines that are frequently more than the scientifically established critical nutrient value (Lopus et al., 2010). A grower-accepted mid-season leaf K CV of >2% is indeed routinely used despite repeated demonstrations that the scientifically established CV is 1.4% K (Reidel et al., 2001). K-applications at uniform high rates across orchards, regardless of the differential plant needs and local soil K availability, occur not only because of sampling and interpretation uncertainty but because the technologies for site-specific variable rate application are not widely available. However, with recent dramatic increases in fertilizer prices, this is wasteful and not economically viable. Improvements in the K management practices have long been limited by the difficulty of precisely determining plant K-availability and the soil response to applied K fertilizer. We have initiated a study to understand the extent and causes of K field variability and its relationship to factors such as soil moisture, clay mineralogy, history of previous treatment, plant uptake rate and distribution. The goal is to provide growers with guidelines to improve their fertilization strategies and the reliability of soil and plant tests and to develop new integrated methods and models, which ultimately would help increase K-use efficiency while reducing K-related costs.
Germani, M. and Brown, P.H. (2024). Causes and implications of potassium variability in orchards (optimizing potassium management in almond). Acta Hortic. 1406, 249-256
DOI: 10.17660/ActaHortic.2024.1406.37
https://doi.org/10.17660/ActaHortic.2024.1406.37
potassium variability, fertilization management, almond orchards
English

Acta Horticulturae