Nutrient release from living and terminated cover crops under variable freeze–thaw cycles

Abstract

Cover crops (CC) are planted into fields during the non-grow-ing season as a best management practice (BMP) for agronomic and environmental benefits. However, freeze–thaw cycles (FTC) may increase the availability of water extractable P (WEP) from damaged plant tissues, leading some to question their efficacy as a nutrient BMP due to their potential to release P during snowmelt. The objectives of this study were to experimentally determine the influence of: (1) FTC magnitude (4°C, −4 to 4°C, –18 to 4°C, and –18 to 10°C), (2) CC species [cereal rye (Secale cereale L.), oilseed radish (Raphanus sativus L. var. oleoferus Metzg Stokes), red clover (Trifolium pratense L.), oat (Avena sativa L.), and hairy vetch (Vicia villosa Roth)], and (3) termination using herbicide on the magnitude of WEP, NH+4, and NO -3 release. Shoot tissue clippings underwent five FTC followed by extraction. Large magnitude FTC from –18 to 4 and –18 to 10°C (heavy frost) elevated WEP release, whereas the −4 to 4°C (light frost) treatment did not. Responses varied with plant type, where frost-intolerant species released more WEP than frost-tolerant species. In contrast, NH+4, and NO -3 release did not increase following FTC. Termination elevated WEP and NH +4 release across all temperature treatments. The use of CC as a nutrient BMP should be used with caution in some regions, but in areas with mild winter climates, growing frost tolerant species without termination may reduce the risk of P leaching from vegetation in winter and early spring.