| Popis: |
Two methods were compared to determine crop nutrient uptake by tomato crops in free-draining perlite substrate. They were the nutrient balance method (applied minus drained) and the dry matter method (DM) (nutrients in plant material). Uptake of N, P, K, Ca, Mg, and S was determined using both methods, in three consecutive tomato crops planted in the same perlite. Nutrient uptake determined using the balance method was consistently higher than with the DM method. Relative differences (balance minus dry matter, with respect to the DM method) were N: −1 to 16%, P: 27–45%, K: 14–46%, Ca: 17–87%, Mg: 28–111%, and S: 15–65%. There was a clear tendency for the difference between the methods to reduce with successive crops. The differences between the methods were reduced when the measured retention of nutrients in the perlite substrate and estimated nutrient retention in roots (using a model) were included. However, these data did not explain all of the observed differences between the two methods. Various retention and loss processes may explain the differences. The results suggest that the DM matter method estimates nutrient uptake by the crop, and the balance method estimates nutrient consumption by the cropping system. |
