Effects of bicarbonate, phosphorus, iron EDDHA, and nitrogen sources on soybeans grown in calcareous soil

Abstract

Hawkeye soybeans (Glycine max L.), an iron‐efficient cultivar when grown in calcareous Hacienda loam soil low in P and available Fe, did not respond to P, FeEDDHA, NH₄+‐N or NO^‐ ₃‐N when applied singly nor to Fe + P together; but did give yield response for N + P + Fe applied together. Addition of HCO₃ ^‐ with N + P + Fe decreased yields by about 10% and decreased Fe in shoots also by 10%. The NH₄+ source of N gave 12% higher leaf yield without HCO₃ ^‐ and 11% higher with HCO₃ ^‐ than did nitrate N. Bicarbonate alone caused severe damage to the Hawkeye soybeans, while P alone had little effect. In contrast, P was very damaging with less effect from HCO₃ ^‐ with iron‐inefficient PI‐54619–5–1 soybeans from a companion study. Addition of Fe decreased Zn and Mn concentrations in leaves, while addition of both Fe and P decreased Zn concentration even more. Bicarbonate contributed additionally to low Zn in leaves with treatments of Fe and Fe + P. These Fe‐efficient Hawk‐eye soybeans were less impaired by NO₃ ^‐ when grown in calcareous soil than were Fe‐inefficient PI‐54619–5–1 soybeans from a companion study.

In a previous study, the Fe‐inefficient PI‐54619–5–1 soybeans were grown in a calcareous soil with various treatments of HCO₃ ^‐, Fe, NH₄ ⁺, NO₃ ^‐ and P singly and in some combinations (Wallace & Abou‐Zamzam, 1984). That study was a follow up of a previous experiment in which NO₃ ^‐ was very inhibitory of growth as was bicarbonate of the PI‐54619–5–1 soybeans in calcareous soil, unless Fe was also applied (Wallace et al., 1981). In that study, however, NO₃ ^‐‐N was not inhibitory of growth without Fe for the Hawkeye soybean cultivar. With Hawkeye, Fe, NO₃ ^‐‐N and HCO₃ ^‐ were fully additive in their responses when applied together. The purpose of the present study was to expose Hawkeye soybeans to the HCO₃ ^‐, Fe, NH₄ ⁺‐N, NO₃ ^‐‐N, P treatments similar to those used for PI‐54619–5–1 soybeans in the 1984 study. One item of interest was whether or not NO₃ ^‐‐N and HCO₃ ^‐ gave additive inhibition as they did with PI‐54619–5–1 soybeans. Also of interest was the question of how HCO₃ ^‐ would influence this Fe‐efficient cultivar when grown in calcareous soil.

There has been renewed interest in the relationship of HCO₃ ^‐to the induction of lime‐induced chlorosis (Chaney et al., 1984; Coulombe et al., 1984a, 1984b; Zhou et al., 1984). Chaney's group has succeeded in controlling nutrient solution to give constant HCO₃ ^‐ levels. Of special interest are studies which indicate that a combination of HCO₃ ^‐ and high P induces Fe chlorosis (Booss et al., 1984; and Kolesch et al., 1984).

Key words:

• Chelate
• zinc
• phosphorus
• iron chlorosis

Notes

The Laboratory of Biomedical and Environmental Sciences is operated for the U.S. Department of Energy by the University of California under Contract No. DE‐ACO3–76‐SF00012.