Genetic gain from selection and potential for improving alfalfa phosphorus uptake and removal from soils heavily amended with poultry litter

Abstract

Alfalfa (Medicago Sativa L.) is increasingly adopted in the southeastern USA as a companion crop in bermudagrass (Cynodon dactylon L.) pastures, where poultry litter is excessively used as source of N fertilizer. This research explores the extent of genetic variation in phosphorus (P) accumulation and uptake in alfalfa germplasm grown in a soil heavily amended with poultry waste, and the expected genetic gain from selection for P accumulation and uptake. Eighteen commercial and experimental populations of alfalfa were evaluated in a soil, heavily amended with chicken litter. The soil pH was 6.8 and Mehlich-1 P content was 1039.7 kg ha−1. Significant genetic variation was observed in P accumulation, forage yield, and P uptake and removal (p < 0.01). Harvest dates effect was significant (p < 0.01), but little interaction of genotypes x harvest date. Narrow sense heritability estimates based on family-means were 0.50 for P concentration, 0.25 for biomass yield, and 0.74 for P uptake. Genetic gain from selection for forage yield based on family means was much higher than that of selection based on individual pots (40 vs. 16 %). For P uptake, gain from selection was 7 % higher using selection based on family means compared to individual pot basis (46 vs. 53 %, respectively). The data suggests that it is possible to make reasonable progress in improving P uptake in alfalfa by selection methods that take advantage of the additive genetic variation such as family selection, whether selecting indirectly for high forage yield or concurrently for P concentration and yield.