The soil Na concentration as a background of fertilizer Na recommendation: A case of sugar beet

Abstract

Sugar beet accumulates a significant amount of Na, which affects both yield of storage root and its technical quality. So far there has not been developed a scientific basis of fertilizer Na recommendation. In order to solve this problem, in 2003 and 2004 series of field trials were carried in commercial farms out to determine the response of sugar beet to Na application. The experiments were established in 20 fields differing in soil Na concentration. Each trial consisted of control (NPK) and a plot with 50 kg Na ha−1 (NPK + Na). Soil samples were collected at two depths (0.0 – 0.3 m and 0.3 – 0.6 m) at spring, before the application of Na. The increase of beet yield (BY) varied from −0.8 to 15.1% compared with the control and averaged at 4.9%. The plants fertilized with Na showed lower sucrose concentration (ca−0.21% fresh matter) and higher root Na concentration (ca +0.65 mM kg−1 fresh matter) compared with the control. The relative increase of white sugar yield (WSY) varied from − 3.5 to 14.1% and was field specific. The effect of Na application on BY and quality depended on the level of plant-available Na. Its impact on WSY was modified by the content of exchangeable K. The highest WSY increase was observed both on Na-poor soils (<6 mg kg−1) and also on soils with K/Na ratio higher than 15–20:1. This study indicates that the diagnosis of plant-available Na content should include both the top- and subsoil. The highest WSY increase resulting from the plant's response to fertilizer Na should be expected on soils with ready-for-use Na content below 60 kg ha−1 within the layer 0.0–0.6 m. In addition, the rate of fertilizer Na for these soils should not exceed 90 kg ha−1.