The objectives of this study were to obtain a reliable index for the evaluation of the S nutrition status in soybean [Glycine Max (L.) Merr.] and to identify the critical S level in relation to seed yield and quality. Two Oxisols were used: A‐horizon soil from Serra dos Gerais, and A‐ and B‐horizon soils from Sambaiba in Maranhão State, Brazil. Soybean plants in pots were grown in a greenhouse with the supply of 0 to 80 mg S kg−1 soil. The seed S concentration was a more reliable index of seed yield because of the higher correlation between S concentration and yield. In the plants with visible symptoms of S deficiency, the seeds contained 1.5 g S kg−1, and the seed yield was 60% of the control. Electrophoresis analysis indicated that the critical seed S concentration for deficiency of protein components was 2.0 g kg−1 when the yield was 80% of the control. The S concentration was 2.3 g kg−1 or higher for >90% yield when the composition of the protein components was identical with that in the original seeds obtained under sufficient S fertilization. We classified the S concentration in the seeds as: deficient (S < 1.5 g kg−1), very low (1.5 ≤ S < 2.0 g kg−1), low (2.0 ≤ S < 2.3 g kg−1), and normal (2.3 g kg−1 ≤ S). Because of stable S concentration, easy sampling, and sufficient time for planning of fertilizer application for the subsequent cropping, seed analysis is preferable to leaf analysis.
No abstract
Six field crops and 7 forage crops were compared in the response to lime and/or superphosphate applications in a field with a soil low in pH and available phosphorus, and the following results were obtained.1. Barley, sugar-beet and alfalfa are very susceptible, and orchard grass, field bean and oat are tolerant to low pH (most probably AI toxicity).2. Red-top, alfalfa and red clover are susceptible, and soybean is tolerant to low P. 3. Tolerance to low pH and that to low P are not associated with each other. When low pH and low P conditions are combined, the adverse effects of these conditions are magnified.4. The adverse effects of these conditions decline with time elapsed after sowing. Thus, in forage crops, except for species which are very susceptible to these adverse conditions, the positive effect of applications of lime and/or superphosphate declines after establishment.
Critical micronutrient concentrations in soils and plants have not been clearly determined for marginal soils where deficiencies are likely to occur. The objective of this study was to develop a reliable method for assessing micronutrient deficiency in soils and plants. Soybean plants [Glycine max (L.) Merr.] were grown in the A and B horizons of two Brazilian Ustoxes and watered with a complete nutrient solution (i.e., control) or solutions lacking one of the following micronutrients: Mn, Zn, B, or Cu. Soybean plants were repeatedly grown in the same soils until maturity. The cumulative frequency of deficient plants where the relative seed dry weight was significantly decreased was recorded. The percent relative cumulative frequency (PRCF) is calculated as: cumulative frequency ÷ total number of tested plants × 100. A linear‐plateau regression line was fitted to the PRCF as a function of the micronutrient concentrations in the soil, the uppermost mature leaf, or seed. Critical concentrations (mg kg−1) for deficiency indicated as transition points of regression lines are: 6.4 for Mn (reference), 1.0 for Zn, 0.2 for B, and 0.2 for Cu in the soil (Mehlich‐I extraction for Mn, Zn, and Cu; hot 0.005 mol L−1 BaCl2 extraction for B); 63 for Mn, 34 for Zn, 25 for B, and 4 for Cu in the uppermost mature leaf; 55 for Mn, 42 for Zn, 14 for B, and 5 for Cu in seeds. Thus, this determination method can clearly identify the critical values for micronutrient deficiency in soils and in plant tissues.
Sulfur deficiency symptoms are more often observed in crops at early stages of growth since S can be easily leached from the surface soil. The objectives of this study were to evaluate some of the popular rotation crops grown in Brazil for tolerance to low external S levels and to determine the critical tissue concentration for S deficiency during early stages of growth. Germinated seedlings of soybean [Glycine max (L.) Merr.], rice (Oryza sativa L.), maize (Zea mays L.), field bean (Phaseolus vulgaris L.), wheat (Triticum aestivum L.), cotton (Gossypium spp.), sorghum (Sorghum bicolor L.), and sunflower (Helianthus annuus L.) were transferred to water culture with 0.0 to 32.0 mg S L–1 and were grown for 29 d. The minimum S concentration required in nutrient solutions was 2.0 mg L−1 for sunflower; 1.0 mg L−1 for cotton, sorghum, wheat, and soybean; and 0.5 mg L−1 or less for field bean, rice, and maize. All crops achieved optimum growth at 2.0 mg S L−1. Critical shoot S concentration at early stages of growth was 0.8 g kg−1 in maize and soybean; 1.1 to 1.3 g kg−1 in cotton, sorghum, and rice; and 1.4 to 1.6 g kg−1 in wheat, sunflower, and field bean. Our results demonstrate that the tolerance to low external S (<2.0 mg L−1) and the critical tissue S levels for deficiency varied significantly among crop species tested.
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