Effect of Boron and Nitrogen on Growth and Chemical Composition of Spinach

Boron toxicity is becoming more extensively widespread in arid and semi arid regions, due to the application of either saline waters or irrigation waters containing a relatively high B content. Results of research indicate that addition of certain plant nutrients such as N may reduce the harmful effect of high B levels. Therefore, the present experiment was undertaken to evaluate the interactive effect as of N and B on the growth and chemical composition of rice in a calcareous soil. Treatments consisted of six B rates (0, 2.5, 5, 10, 20 and 40 mg kg-1 as boric acid) and four levels of N (0, 75, 150 and 300 mg kg-1 as urea) arranged in a factorial manner in completely randomized design of three replicates.Application of B decreased shoot dry matter. In treatments with low B concentrations, N application alleviated the toxic effect of B. In the absence of B, application of 300 mgN kg-1 of soil caused an increase in dry matter weight by 55% as compared with control plants. Minimum of dry matter weight was in the absence of N with addition of 40 mg B kg-1 of soil (N0B40). Moreover, it was observed that the addition of B increases B and N concentrations in the aerial parts of the spinach plant. The N concentration increased while B accumulation decreased with increasing N rates. Application of N and B increased proline concentration in fresh leaf. Chlorophyll concentration decreased with increasing B levels. N fertilization increased chlorophyll content and somewhat reduced the adverse effects of high B rates on this plant parameter. There was a general trend of increase in chlorophyll concentration in fresh leaf with increasing chlorophyll meter readings. Application of B decreased mean Ca: B ratio in the spinach shoot, significantly due to B concentration getting increased with increasing B rates. But at all B levels, there was a general trend of increase in this ratio with application of N. The results reported herein show that in soils with high B levels, N application may alleviate the suppressing effects of B toxicity and increase rice growth, possibly due to a diminishing trend in B absorption by the plant.