The earthworm species Pheretima hawayana influences organic wastes decomposition, nitrogen mineralization and maize N recovery

We investigated the influence of the anecic earthworm Pheretima hawayana (Rosa, 1891) on decomposition, nitrogen (N) mineralization and maize apparent N recovery from farmyard manure (M), wheat straw + M (WSM), maize straw + M (MSM), compost (CO), and slurry (SL) applied to a sandy loam soil. Results revealed that inoculation of earthworm in organic waste treatments significantly increased CO2 emission (P = 0.02). The earthworms' induced CO2 emission was the highest in MSM and the lowest in M treatment. Earthworms did not influence total dry matter yield or N uptake by maize (P > 0.05), however, organic wastes significantly affected these parameters (P < 0.01). Overall, earthworm enhanced apparent crop N recovery from M, CO and SL treatments by 543, 105, and 109%, respectively. Out of the total N applied, about 14, 8, 6, 2, and -11% was recovered in maize plants from M, SL, CO, MSM and WSM, respectively. The lower apparent N recovery in MSM and WSM could be attributed to the higher C:N ratio of these crop residues that may cause N immobilization. This was confirmed from the calculated N balance of WSM treatment, where net immobilization equal to 15% of the organic N was occurred. Despite of higher CO2 emission from WSM and MSM, earthworm could not increase maize N uptake or N recovery from crop straw treatments. Hence, in short interval-cropping systems like maize, earthworms may need an extra available N source to improve crop growth, where crop residues are part of fertilizer management strategy.