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

Abstract

Potassium (K) efficiency and its depletion in the rhizosphere of summer wheat (Triticum aestivum L. cv. Planet), maize (Zea mays L. cv. Pirat), and sugar beet (Beta vulgaris L. cv. Orbis) was studied in a pot culture experiment with Anglberg sandy clay loam soil from Bavaria, Germany having 50 μM K (K1), 140 μMK (K2), and 1,700 μM K (K3) 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 maximum dry matter yield at 50 μM K in soil solution. Increasing level of K did not affect dry matter yield, while K content of plants increased three times. Wheat and maize dry matter yield increased by 60 and 30%, respectively, with increase in soil solution K to 140 μM suggesting that sugar beet 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 and 2 times higher shoot demand on root than wheat and maize, respectively. On the other hand sugar beet had four times higher K influx at 50 uM 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 showed that initial soil solution K concentration of 50 uM at the root surface decreased to as low as 2.7 uM for sugar beet compared to 9.3 uM for maize and 13 uM for wheat alter 11 days of uptake. According to these calculations the higher influx of sugar beet was due to its capability to decrease the K concentration at the root surface to a lower value thereby increasing the concentration gradient and so the transport to the root surface. Mathematically modeled soil and plant parameters satisfactorily predicted K influx, however at Kt level model over predicted K influx for wheat and maize and under predicted for sugar beet. Sensitivity analysis demonstrated that at K1 level CLi was the most sensitive factor increasing K influx in wheat, maize, and sugar beet. Increasing Imax increased K influx in wheat and maize, but did not help increasing K influx in sugar beet.