Multiple soil health indicators are responsive to summer cover crops on an irrigated organic farm

Abstract

While cover crops (CC) are known to enhance soil health, outcomes are often subtle and confined to a shallow surface soil layer. We assessed 15 soil health indicators over three CC trials with a 15-species Blend polyculture, a Mustard biculture {white [Sinapsis alba L.] and brown [Brassica juncea (L.) Czern.] mustards}, Buckwheat (Fagopyrum esculentum Moench), and Faba bean (Vicia faba L.) monocultures, and a Weedy fallow (no CC, weeds allowed to grow) on an organic farm in southern Alberta. Soil sampling times included (i) summer pre-termination; (ii) fall post-termination; and (iii) spring post-termination of CC. Twelve of 15 soil health indicators showed significant effects of CC treatment for at least one sampling time. Soil organic C (SOC) ranked highest with 80% of sampling times showing significant CC effects. N-related indicators [total N (TN), nitrate-N)] were also quite sensitive, being significantly affected by CC treatment at 60% of sampling times. Three soil health indicators [acid phosphomonoesterase (AcP), wet aggregate stability, and free-living nematodes (FLN)] were consistent in their non-responses to CC treatment at all sampling times. Comparing CC treatments with a Weedy fallow, showed that not all enhancements of soil health were explained by inclusion of a CC, with Weedy fallow as effective for some indicators. A polyculture Blend significantly enhanced soil health over a monoculture CC or Weedy fallow in 46% of instances of soil health indicator improvement. While CC led to enhancement of soil health, results were not always consistent, being contingent on specific indicators.