Influence of magnesium deficiency on chestnut (castanea sativa mill.) yield and nut quality

Abstract

Under conditions of poor management, severe Mg-deficiency is often observed in chestnut groves located on base-poor granites and schists, in NE Portugal. Many of the severe cases of Mg-deficiency are due to nutritional imbalances between Mg and a growth-stimulating nutrient, particularly nitrogen. In areas affected by Mg-deficiency sharp contrasts have been observed between chlorotic and symptom-free trees, particularly in young groves. A 20-years-old chestnut grove of a traditional Portuguese variety, Longal, was selected in order to study the influence of Mg-deficiency on several tree growth parameters, yield and chestnut quality. Trees were classified according to the intercostal yellowing chlorosis of their leaves into three categories: symptom-free, slight chlorosis and acute chlorosis. There is a strong negative correlation between severity of chlorosis and foliar Mg concentration, tree growth parameters, chestnut production and fruit quality. The mean Mg concentration in leaves of symptom-free trees was 1.2 g kg⁻¹ and the lowest value in green leaves was 0.85 g kg⁻¹. Severe intercostal chlorosis was observed when the Mg concentration in leaves was lower than 0.55 g kg⁻¹. The N/Mg ratios increase with the severity of the deficiency, reaching values higher than 40 in the leaves of trees with more acute deficiency. Shortage of Mg causes poor growth of chestnut trees, severe yield reduction and lower nut calibre; nuts have lower levels of dry matter content and crude fat, but higher crude protein content.