1985 Volume 53 Issue 4 Pages 427-431
Six species of vegetable crops were grown in solution culture in order to investigate the effect of form of N supplied and pH level of the nutrient solution on Zn toxicities in vegetable crops. Zinc was supplied at levels of 0.05, 3 and 10ppm. At each Zn level, NO3, NO3+NH4(1:1) and NH4 were supplied, with the total N concentration being held constant at 12me/l. The pH of the nutrient solution was adjusted to two levels, 4 and 6. Plants were grown under different treatments for about three weeks.
1. At the normal Zn level (0.05ppm), plants supplied with NH4 developed various NH4 injury symptoms. In some vegetable crops excess Zn associated with pH 6 and NO3 developed Zn-induced chlorosis, which was not observed in NO3+NH4 and NH4 treatments. Under pH 4 this symptom was scarcely observed.
2. At the normal Zn level, the growth of plants supplied with NO3 and NO3+NH4 was almost equally good, but NH4 plants produced much more inhibited growth. Excess Zn in the nutrient solution inhibited the growth of plants supplied with NO3and NO3+NH4, but in most cases NO3+NH4 produced better growth than NO3.The growth of plants supplied with NH4 was almost constantly poor regardless of the Zn level in the nutrient solution. Under Zn excess condition, pH 4 often produced better growth than pH 6 in NO3 and NO3+NH4 treatments.
3. Increasing proportion of NH4 supply and low pH had effects to inhibit the accumulation of Zn in leaves. In NO3 and NO3+NH4 treatments, the more the accumulation of Zn in leaves increased, the more the growth was inhibited regardless of N treatments. In NH4 treatment, however, the growth of plants was almost constantly poor regardless of leaf Zn concentration.
4. It may be concluded that NH4+ and H+, unless their own levels are injurious, exert marked effects in reducing Zn uptake and Zn toxicities in vegetable crops.