Root production and root mortality of winter barley and its implication with regard to phosphate acquisition

Abstract

Winter barley was grown in a long-term fertilizer experiment (14 years) using two P treatments: (i) no P fertilization over the whole time (−P) and (ii) an annual fertilization of 44 kg P ha⁻¹ (+P). The objective of the study was to investigate the influence of the P supply on total root production and root mortality (i.e., root turnover) and to assess the benefit of a more rapid root turnover on P acquisition. Shoot development and grain yield was reduced in the ‘−’ treatment, whereas the standing root system had nearly the same size as in the ‘+P’ treatment. Gross root growth was measured using the ‘ingrowth core method’. Mesh bags filled with root-free soil were buried into the rooting zone (0–30 cm) and root growth into the bags over periods of 2–3 weeks was determined. Assuming that no root mortality occured inside the bags during this short period, root length in the bags will be a measure of total root production. Total root production between April and June exceeded the size of the standing root system by a factor of 2 to 3 and was significantly higher at P deficiency. Root mortality as the difference between total root production and the size of the standing root system was also increased at P shortage. P uptake was calculated by using a mechanistic transport and uptake model. Calculations based on gross root growth and root mortality resulted in a higher uptake than calculations based on the development of the standing root system, although the length of the active roots were the same in both calculations. This was due to a better exploitation of undepleted soil areas by the growing root system. The root renewal by a continuous root growth and root mortality is discussed as a mechanism of P uptake efficiency.