Can Nutrient Uptake Models be Used to Improve Potassium Management in Maize Production Systems?.

Soil potassium (K) availability and acquisition by plant root systems are controlled by complex, interacting processes that make it difficult to assess their individual impacts on crop growth. Mechanistic, mathematical models, such as NST 3.0, provide an important tool to enhance our understanding of these processes, and can enable better management of crop K nutrition. Current mechanistic models describe soil K supply by mass flow and diffusion to root surfaces. Root surface absorption of K follows Michaelis-Menten kinetics. Root growth rate is considered; however, model calculations have generally been based on a single, cylindrical root, rather than a three dimensional root system. Under controlled conditions, existing models can adequately calculate K uptake by growing roots. Problems generally arise when a biotic or abiotic process affects root system function, thus violating the assumptions built into the models. For example, previous research suggests that root exudates can mobilize soil K or influence release of non-exchangeable K. Further, K has a predominant role in osmoregulation and in maintaining cation-anion balance within cytoplasm, and these functions can be partially replaced by other cations and/or organic compounds. Such substitutions pose significant challenges to mechanistic representation of plant demand. Our objective in this study was to better understand the K uptake mechanisms of maize (Zea mays L.) under low K supply. Soil and plant parameter data from previous studies were utilized to determine whether uptake kinetics alone could explain differences in measured and calculated influx under low K supply or mobilization of K in the rhizosphere should be considered.