Species and termination method effects on phosphorus loss from plant tissue

Cover crops are often recommended as a best management practice to reduce erosion, weed pressure, and nutrient loss. However, cover crops may be sources of phosphorus (P) to runoff water after termination. Two greenhouse trials were conducted to determine the effects of cover crop species, termination method, and time after termination on water-extractable P (WEP) release from crop biomass. Treatments were structured in a 3 × 3 × 3 factorial and arranged in a randomized complete block design with six replicates. Treatments included three cover crop species (triticale [× Triticosecale; Triticum × Secale 'Trical'], rapeseed [Brassica napus L. 'Winfred'], and crimson clover [Trifolium incarnatum L.]); three termination methods (clipping, freezing, and herbicide); and three WEP extraction times (1, 7, and 14 d after termination). Rapeseed consistently resulted in the least WEP when exposed to the same method of termination and at the same extraction time as the other species. For both trials, terminating crop tissue via freezing increased concentrations of WEP compared with other termination methods. The WEP release from cover crop tissue increased as the time after extraction increased, but the effect was greater for herbicide- and freeze-terminated cover crops and less for clipping-terminated cover crops. Future studies on WEP release from cover crops should pay close attention to the effects of extraction timing. Producers may be able to reduce P loss from cover crop tissue by selecting cover crop species with low WEP and minimizing the amount of biomass exposed to freezing conditions.