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Root renewal of sugar beet as a mechanism of P uptake efficiency
No full textSugar beet (Beta vulgaris L.) was grown in two different longterm P fertilization experiments on a sandy and a loamy soil. The P supply levels of the soils were "low", "sufficient", and "high", according to the German recommendation scheme. The low P level decreased shoot and storage root yield only on the loam soil, where the recovery of the P-deficient plants after a drought period was slower than at a sufficient P supply. The size of the living root system, as determined by a conventional auger sampling method, peaked at early July and decreased until harvest on the sandy soil without any influence of the P level. On loam, the living root systems were more constant and larger at P shortage. Total root production, as determined by the ingrowth core method, was about 120 km, m(-2) in the well P supplied loam treatments and 200 km m(-2) at P deficiency, which was 3-4 times and 5 times higher than the average size of the living root systems, respectively. Hence, a rapid root renewal took place. On sand, where no P deficiency occurred, total root production was not different between the P supply levels but higher than in the well-supplied loam treatments. Modelling P uptake revealed that this root turnover and the concomitant better exploitation of the soil facilitates P uptake at a low P level in soil, but is of no advantage at a sufficient P supply. The increase of root production at P shortage increased calculated P uptake by 25% compared to a calculation with the "usual" root production at a sufficient supply
A sensitivity analysis for assessing the relevance of fine‐root turnover for P and K uptake
No full textPlant fine roots are subject to continual turnover, i.e., old roots die during the plant life cycle and are quickly replaced by new roots. New roots grow partly into undepleted soil areas and can take up nutrients at a higher rate than old roots. This is one possible advantage of root turnover. It has been shown that root turnover of several plant species increases when P and/or K supply is limited, indicating an efficiency mechanism. The objective of this study was to assess the maximum benefit for nutrient uptake by root turnover and to determine which soil or plant properties influence this process. Based on a data set of field-grown faba beans, a sensitivity analysis with a transport and uptake model was performed, i.e., several input parameters were systematically varied to assess their importance for nutrient uptake of a root system with and without fine-root turnover. The calculations were based on the assumptions that all new roots grow into undepleted soil areas and that no inter-root competition occurs. Model calculations indicated that a root system with a high but realistic turnover rate can take up twice the amount of P or K compared to a stable root system without any turnover. This benefit on uptake is higher at low concentrations of these nutrients in soil solution, low soil water content, or high maximum inflow. However, measured uptake under poor conditions of nutrient supply is often higher than calculated uptake, even when root turnover is taken into account. This indicates that root turnover might be an efficiency mechanism, but not the only one
Potassium dynamics in the rhizosphere and K efficiency of crops
No full textNutrient efficiency is defined as the ability of plants to obtain higher relative yields at low nutrient supply compared to other species. The size of the root system, the physiology of uptake and the ability of plants to increase K solubility in the rhizosphere are considered as mechanisms of uptake efficiency. In a solution experiment wheat and sugar beet were more K efficient than potato because wheat had a large root system and both species had an efficient uptake physiology. Also in soil wheat was uptake efficient because of a large root system, whereas the efficiency of sugar beet was caused by the ability to increase K solubility. This could be shown by the use of a model to describe K dynamics in the rhizosphere
L.) and its interaction with P and K supply
No full textAn increased root turnover can be a mechanism of improved nutrient-uptake efficiency. The objectives of this study were to investigate P and K efficiency of faba beans (Vicia faba L.), to determine their root growth and root turnover, and to assess the relevance of root turnover on P and K uptake at limited supply. Faba beans were grown as part of a long-term fertilization experiment on fertilized plots (control) and plots that had not received any P or K fertilizer for 16 years (PO, KO). Although the unfertilized soils were low and very low in their P- and K-supply level, respectively, no differences in shoot-dry-matter production occurred compared to the control. However, relative K concentration in dry matter of the KO plants (control plants = 100) decreased during the experiment and was only 60% of the control at the final harvest. This indicated a high K-utilization efficiency of faba bean. Relative phosphorus concentration increased in the PO treatment and was not different from the control at the last harvest, indicating an improvement in P-uptake efficiency with time. The size of the standing root system determined by sequential auger sampling (net development) was not influenced by P and K supply. Total root production as measured by the ingrowth-core method was about 6 times higher than the average size of the standing root system and even increased under low-K conditions. This indicated a fast root turnover. Modeling soil nutrient transport and uptake revealed that calculated uptake of the control was up to 48% higher when root turnover was taken into account, compared to calculations based on the net development of the root systems. This is due to a better soil exploitation. Under K shortage, root turnover resulted in a 117% higher calculated uptake, which was close to measured K uptake. Root turnover was also of benefit for P uptake, but calculated P uptake was significantly less than measured, indicating that root turnover was of little importance for P uptake of faba beans
Calculation of the total nitrate uptake of lettuce (Lactuca sativa L.) by use of a mathematical model to simulate nitrate inflow
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