Objectives The impact of maize straw derived organic materials on soil fertility and maize yield was studied, to provide reference for efficient use of straw resources.

Methods A field experiment was conducted for five years in Gongzhuling City, Jilin Province. The treatments included: no-fertilizer control (CK), sole chemical fertilizer (NPK), NPK plus maize straw (NPK+ST), NPK plus straw biochar (NPK+BR), and NPK plus straw compost (NPK+CP). The three organic amendments had similar annual carbon input of 3200 kg/hm². Soil samples were collected in 0–20 cm and 20–40 cm depth for determining soil organic carbon (SOC), labile organic carbon (LOC), available nutrients and enzyme activities. Maize yield over time was also evaluated.

Results Compared with NPK, NPK+BR significantly increased SOC in 0–20 cm and 20–40 cm soil by 28.2% and 11.2%, respectively, while NPK+CP and NPK+ST only significantly increased the SOC at 0–20 cm soil by 15.5% and 7.6%. Organic amendments had significantly ( P 0.05) higher LOC contents than NPK at the two soil depths. The soil LOC contents at 0–20 cm depth of NPK+CP and NPK+ST treatments were 13.2% and 8.7% higher than that of NPK+BR, respectively. All the organically-based amendments significantly increased the available P content at 0–20 cm soil depth, but only NPK+CP and NPK+BR treatments did at 20–40 cm soil depth. Available N was higher in NPK+CP treatment at 0–20 cm soil depth than those in NPK+ST and NPK+BR. The three organically-based treatments significantly increased the activity of soil cellulase, invertase and phosphatase at 0–40 cm soil depth. The NPK+ST and NPK+BR treatments resulted into higher cellulase activity than NPK+CP treatment, whereas NPK+ST improved invertase activity than NPK+BR and NPK+CP treatments. Higher phosphatase activity was exhibited in NPK+ST and NPK+CP treatments. Application of the organically-based amendments increased maize yield during the five years. The average maize yield in order was: NPK+CP＞NPK+ST＞NPK+BR＞NPK＞CK.

Conclusions Biochar plus NPK markedly increased soil organic carbon at 0–40 cm soil depth, while straw and compost comparably enhanced the liable organic carbon content. Compost application resulted in higher soil available N than straw and biochar only at 0–20 cm soil layer but biochar and compost increased available P contents at 20–40 cm layer. Straw and biochar increased cellulase activity of soil at 0–40 cm, while straw and compost improved invertase and phosphatase activities. Therefore, biochar is recommended for the rapid enhancement of soil organic carbon content, while straw and compost are suitable for increasing the nutrient availability in Mollisol.