Banded phosphorus effects on alfalfa seedling growth and productivity after temporary waterlogging

Phosphorus applied in a band below alfalfa (Medicago sativa L.) seed can increase seedling growth. A field study was conducted to evaluate the effect of banded-P and temporary flooding stress on alfalfa seedling growth in the autumn and subsequent productivity. Experiments were seeded in late August 1994 and 1995 at two locations in Ohio on soils having P levels typical for the region. Fertilizer treatments included no fertilizer P and 27 kg P ha^-1 (62 kg P₂O₅ ha^-1) banded under the seed. Flooded and unflooded treatments were imposed 21 to 26 d after seeding. Flooding was maintained for 11 to 18 d, then plots were allowed to drain naturally. Before flooding was imposed, banded-P increased seedling dry weight by an average of 60%. Flooding reduced seedling dry weight regardless of P treatment. At end of the flooding period, seedlings with banded-P were larger than the flooded, no-P controls at three of the four locations. In November, flooded seedlings with banded-P had greater root dry weight at two locations and greater shoot dry weight at one location compared with the flooded, no-P controls. Flooding in the autumn reduced dry matter yield the next year at two locations. In 1995, banded-P increased yield the year after seeding ~15% in the unflooded treatment at one location and ~15% in the flooded treatment at the other location. Although banded-P increased seedling growth in the autumn regardless of flooding treatment, its effect on stand density and yield the year after establishment was minimal.