Bermudagrass management in the southern Piedmont USA. II. Soil phosphorus

Plant production can be limited by low levels of available P due to high P-fixation capacity in soils of the southeastern USA. On the other hand, there is increasing concern about excessive application of P to soil, especially when manure application is based upon N content. We evaluated changes in Mehlich-1 extractable soil P during 5 yr of bermudagrass [Cynodon dactylon (L.) Pers.] management varying in fertilization [inorganic and broiler chicken (Gallus gallus) litter] and harvest strategy (unharvested, low and high cattle (Bos taurus) grazing pressure, and haying). Broiler litter supplied eight times more P than inorganic fertilization to meet the N requirement. At a depth of 0 to 6 cm, Mehlich-1 extractable soil P increased 0.8 +/- 1.6 mg kg(-1) yr(-1) (4 +/- 8% of total P added) with inorganic-only fertilization,2.4 +/- 3.0 mg kg(-1) yr(-1)(9 +/- 11% of total P added) with clover (Trifolium incarnatum L.) cover crop plus inorganic fertilization, and 8.7 +/- 9.8 mg kg(-1) yr(-1) (6 +/- 7% of total P added) with broiler litter. Haying kept Mehlich-1 extractable soil P constant with time due to removal of P with harvest of biomass. At the end of 5 yr of broiler litter application to grazed land, Mehlich-1 extractable soil P was 135, 50,22, and 4 mg kg(-1) higher than with inorganic fertilization at depths of 0 to 3, 3 to 6, 6 to 12, and 12 to 20 cm, respectively. Broiler litter fertilization was effective at increasing Mehlich-1 extractable soil P to an agronomically productive level (50 to 60 mg kg(-1) 15 cm(-1)), but continued application could lead to excessive P accumulation that could threaten water quality from surface runoff unless appreciable soil fixation or removal of forage biomass were to occur.