Nitrate utilization and carbohydrate distribution as affected by nitrogen and potassium nutrition in sugar cane plants

Abstract

The experiment was carried out in a greenhouse and in nutrient solutions with three combination of with three K levels each combination. The N and K levels, alone, affected the dry matter distribution between roots, stalks and leaves, more than N-K interactions. N and K-deficient plants presented the lowest growth of leaves and stalks, respectively. The N₂K₃ combination promoted the largest dry matter accumulation in the stalks. These plants showed lower nitrate and soluble N-amino concentrations and lower nitrate reductase activity than N₂K₁ and N₂K₂. The protein concentration was altered only by N deficiency. The N conversion index (kg of stalk/kg of N) was reduced by increasing N levels and in K-deficient plants. The highest N levels caused decreases in the concentrations of sucrose and reducing sugars in leaves and stalks. The N₂K₃ combination showed the highest levels of sucrose in leaves and stalks. The highest yield in N₂K₃ combination may be related with higher photosynthetic efficiency, higher sucrose translocation to the stalk and lower energetic costs of nitrogen utilization.