Potassium efficiency and dynamics in the rhizosphere of wheat, maize, and sugar beet evaluated by a mechanistic model

Potassium (K) efficiency and its depletion in the rhizosphere of summer whe at (Triticum aestivum L. cv. Planet), maize (Zea mays L. cv. Pirat), and su garbeet (Beta vulgaris L. cv. Orbis) was studied in a pot culture experimen t with Anglberg sandy clay loam soil from Bavaria, Germany having 50 mu M K (K-1), 140 mu M K (K-2), and 1,700 mu M K (K-3) in soil solution. Soil and plant parameters were determined to evaluate nutrient uptake model NST 3.0 which takes into account contribution of root hairs. Sugar beet produced m aximum dry matter yield at 50 mu M K in soil solution. Increasing level of K did not affect dry matter yield, while K content of plants increased thre e times. Wheat and maize dry matter yield increased by 60 and 30%, respecti vely, with increase in soil solution K to 140 mu M suggesting that sugar be et had higher K efficiency than wheat and maize. Sugar beet had the lowest root/shoot ratio but highest relative shoot growth rate resulting in 3.2 an d 2 times higher shoot demand on root than wheat and maize, respectively. O n the other hand sugar beet had four times higher K influx at 50 mu M K in soil solution than wheat and maize. Thus, the higher K efficiency of sugar beet was because of higher K influx. Nutrient uptake model calculations sho wed that initial soil solution K concentration of 50 mu M at the root surfa ce decreased to as low as 2.7 mu M for sugar beet compared to 9.3 mu M for maize and 13 mu M for wheat alter 11 days of uptake. According to these cal culations the higher influx of sugar beet was due to its capability to decr ease the K concentration at the root surface to a lower value thereby incre asing the concentration gradient and so the transport to the root surface. Mathematically modeled soil and plant parameters satisfactorily predicted K influx, however at K-1 level model overpredicted K influx for wheat and ma ize and under predicted for sugar beet. Sensitivity analysis demonstrated t hat at K-1 level C-Li was the mast sensitive factor increasing K influx in wheat, maize, and sugar beet. Increasing I-max increased K influx in wheat and maize, but did not help increasing K influx in sugar beet.