Effect of cultural practices on the manganese status of soil and citrus trees under irrigation.

Abstract

The occurrence of manganese deficiency in citrus on an experimental orchard established in light horticultural soil in the Murrumbidgee Irrigation Area is reported. There is a relationship between visual symptoms of deficiency and the amount of manganese in the leaf. When the leaf manganese falls to 20 p.p.m., 50 per cent. of the trees show visual deficiency symptoms. Trees on Sweet Orange stock had less manganese and showed more visual deficiency symptoms than trees on Rough Lemon stock. A decrease in soil pH consequent on the addition of ammonium sulphate fertilizer led to a graduated increase in exchangeable soil manganese and leaf manganese. Bringing the calcareous subsoil to the surface consequent on digging trenches for laying agricultural drains led to acute manganese deficiency. Trees on plots tilled during the summer have greater leaf manganese contents than trees on sod plots or plots not tilled but kept free of weeds by herbicidal sprays, but these cultural treatments do not affect the exchangeable soil manganese. Possible reasons for the differences are discussed.