Crop production in acid soils may be limited by several factors, including low pH. Development of acid‐tolerant cultivars requires information about differences in tolerance to low pH among crop genotypes. To determine whether differential responses to nutrient solution pH occurred among seven maize (Zea mays L.) genotypes, seedlings were grown in a growth chamber in flowing solutions at pH levels ranging from 3.3 to 6.7. Top weights, root lengths and weights, and concentrations of Ca, Mg, Fe, Zn, and Mn in plant tops were determined after 12 d. All genotypes grew well with pH of 4.0 to 5.5, with maximum dry weights of plant tops at pH 4.6 for most of the genotypes. However, all genotypes had necrotic root tips and decreased root lengths at pH 3.3, with relative root lengths (length at pH 3.3/maximum length) ranging from 0.26 to 0.55. Root weights were relatively unaffected by solution pH, but top weights decreased markedly at both pH extremes. Iron concentrations of all genotypes were decreased at pH 6.7, and interveinal chlorosis, resembling Fe deficiency, appeared in the younger leaves. Relative top weights (weight at pH 3.3/maximum weight) averaged 0.79 for Trinidad Grpl&2 and ‘PDMR Comp 1’ and 0.58 for ‘UPCA Varl’, ‘PDMR3’, Kalimpos, and Dikit at pH 3.3, and relative top weights among genotypes were positively correlated (r = 0.85) with Mn concentrations in tops. Based on relative top weight at pH 3.3, the former two genotypes were relatively more tolerant of extremely low pH than those in the latter group.

No abstract

Responses of soybean (Glycine max L.), mung bean (Vigna radiata L.), and corn (Zea mays L.) to CO(NH2)2, CaCO3, Ca(H2PO4)2·H2O, and CaSO4, and of legumes to single strain Rhizobium inoculants on a Vertisol was determined during the dry season at Los Banōs, Philippines. Irrigation well water and precipitation were used to maintain soil moisture slightly below saturation in 6‐kg crocks. Relevant chemical analyses were made on soils, water, and plants. Inoculation increased N concentration of soybean tops. Soybean yield was greater with seed inoculation before planting than without, but mung bean did not respond to seed inoculation before planting. Neither legume responded to 30 kg N/ha as urea. Nodules on legume roots were greatly increased by 40 kg P/ha. All yields were more than doubled by addition of 40 kg P/ha. Increased yield of corn and soybeans resulted from the addition of 20 kg S/ha. The addition of sulfur as CaSO4 resulted in an increased soil S concentration as measured by dilute NH4C2H3O2, CH3COOH extraction.