Influence of soil characteristics on yield response to lime in sugar beet

Abstract

Sugar beet is an economically important crop grown on around 30,000 ha in the province of Skåne in the south of Sweden. This project examined the effects of lime on soil factors and yield response in sugar beet in 52 soils in Skåne. Previous research in sugar beet in this area has postulated the importance of appropriate calcium concentrations in the soil to avoid yield losses caused by the root pathogen Aphanomyces cochlioides. Field trials on liming in Sweden have, however shown contrasting results on yield and subsequent economic benefits. The practice of liming has therefore been neglected and resulted in suboptimal pH for plant growth and development in many soils. The aim of the present investigation was to identify and evaluate soil factors of importance for a positive yield response in sugar beet after application of two different lime products: factory lime and limestone meal in rates with similar neutralizing effect (4 tons CaO/ha). Data on soil texture, cation exchange capacity (CEC) and clay mineralogy were available for each site. After liming, nutritional status and Aphanomyces root rot potential in the soil were analysed in each treatment and finally the yield was measured. In total, 52 soils were treated with the two lime products. In addition, 12 of these were also treated with increasing doses of limestone meal.In average for all 52 soils, the yield increased significantly after treatment with either of the lime products. Similarly, the root rot potential of A. cochlioides decreased significantly with no difference between the products. In 12 field trials with 4, 8, 16 and 32 ton/ha limestone meal, 8 ton/ha gave the highest yield. In classifying the soils according to pH and prevailing recommendations, soils with an initial pH >7.0 and with no liming requirement responded positively with significant increases in sugar yield. Soils with initial pH 6.5–7.0 and with a liming requirement, showed less response, with no significant increase in sugar yield. However, the concentration of calcium increased above the suggested threshold of 250 mg/100 g soil and the root rot potential of A. cochlioides decreased significantly in this group. For soils with an initial pH <6.5, the calcium content remained unchanged after liming. Also, Aphanomyces root rot, which was most prevalent in these soils, was not affected by liming. These soils have a low buffering capacity due to the combined effects of clay mineralogy with a low proportion swelling clay minerals and a low clay content. Sugar beets have been shown to acidify the rhizosphere and a high buffering capacity and a high base saturation maintain an optimal pH for nutrient uptake. The results suggest that for crop rotations including sugar beet, liming should be done on a regular basis, also for soils with a pH >7.0. It is of special importance in soils with low pH and CEC to maintain or increase calcium concentrations to a level >250 mg/100 g, which reduce the propagation of A. cochlioides.