Three experimental systems to evaluate phosphorus supply from enhanced granulated manure ash
Three experimental systems were used to evaluate a new P fertilizer since residual P levels at typical farm sites may make response detection unlikely. The systems were (i) greenhouse with low P soil, (ii) long-term research sites with preexisting soil P gradients, and (iii) agricultural fields with prior P fertilization based on agronomic recommendations. The new fertilizer (animal waste by-product, AWP: 5% N, 28% P2O5, 4% K2O, and 1% S) is an enhanced granulated manure ash. Corn (Zea mays L.), wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.] growth, P uptake, and residual soil Mehlich-3 P were measured with agronomic rates of AWP or triple superphosphate (TSP). Greenhouse corn and wheat P uptake, and soil Mehlich-3 P increased similarly with either fertilizer at rates equivalent to 0, 10, 20, 40, and 80 kg P ha–1. In long-term research sites, grain yield increased with P fertilization in 8 of 12 tests, and was greater with TSP than with AWP in 3 of 12 tests. Plant P uptake increased in all 12 tests, and was greater with TSP in 1 of 12 tests. In previously fertilized agricultural fields, soil Mehlich-3 P, but not yield, increased due to P fertilization. Fertilizer source differences were infrequent and relatively minor, but possibly due to lower water soluble P content of the AWP (70% versus 78% for TSP). Evaluation of such products requires an appropriate experimental system with low P soils that may be difficult to find on typical North Carolina farms.