Soil C, N and P bioavailability and cycling following amendment with shrub willow chips

Potato (Solanum tuberosum L.) crops are often cultivated in coarse-textured soils with low soil organic matter (SOM), and high nitrate leaching risk. Incorporating shrub willow chips into soil could enhance soil properties, while temporally immobilizing N and thus reducing N leaching. We performed a laboratory incubation study and a field experiment to evaluate the effects of shrub willow chips applied at increasing rates in the fall after the potato harvest on C, N and P cycling, soil pH and moisture, and on barley (Hordeum vulgare L.) yield in the following year. In comparison with the control, willow chip incorporation at the rates of 40 Mg ha-1 and 60 Mg ha-1 increased total C content, but it did not affect the activity of C cycling enzymes. Willow chip addition at these rates also induced nitrate immobilization and reduced barley grain yield and total N uptake, but increased the activity of N cycling enzymes (β-1,4-N-acetylglucosaminidase and leucine aminopeptidase). Mehlich-3 extractable P content and phosphomonoesterase activity were not affected by willow chip addition. Our results suggest that shrub willow chips increased total organic C and immobilized N following their incorporation and can thus mitigate nitrate leaching after the potato harvest. The N immobilization was short-lived and was not observed over second winter. We recommend to seed a forage legume in the spring following shrub willow chip incorporation. Willow chip incorporation is an effective means of increasing soil organic carbon.