Nodule and Plant Development in the Soyabean, Glycine max (L.) Merr.: Growth Response to Nitrogen, Phosphorus and Sulfur

The effects over a wide range of interaction of sulfur (S) (5 levels) × phosphorus (P) (5) × nitrogen (N) (6) on nodulation and development of the soybean growing in a nutrient-deficient soil are described for three growth stages: flowering, pod-fill and seed maturity. There were consistent main effects for all three nutrients, but interactions changed from nil at flowering to a few P × N and P × S at pod-fill; and then to predominant P × S at maturity for the principal plant parts. Nodulation was extremely sensitive to levels of nutrient combination, with extremes of nutrient imbalance reducing nodulation almost to zero. Conversely, well-balanced combinations favoured nodulation right through growth until maturity, the best nodulation occurring at high levels of all three nutrients. The yield of seed was not affected by nitrogen supply when sulfur and phosphorus were adequate for an effective nitrogen symbiosis. Introduction