Organic materials improved the soil fertility in Carya cathayensis forest lands

Objectives  The great differences in soil productivity and soil fertility are existed among the forest soils with low-yielding and high-yielding Carya cathayensis. Comparing the differences of organic materials on the improvement of soil acidity and fertility will provide a theoretical guidance for the effective application of organic materials.

Methods  Carya cathayensis forest lands originated from red soil (low-yielding) and limestone soil (high-yielding) were chosen for the two independent incubation experiments. Four kinds of organic materials, bio-organic fertilizer (BF), potassium humate (KH), bamboo-char (BC) and biogas residue (BR), were supplied into the soils by the rate of 1% accounting for total soil weights, and incubated at a constant temperature of 25℃. Soil samples were collected at 0, 30, 60, 90 and 180 d to measure the soil pH, available N, available P, available K and available micronutrients of Fe, Mn, Cu and Zn, respectively.

Results  1) Red soil after incubation of 180 days, organic materials affected nutrient availabilities in different levels. Available N was only significantly increased in the BR treatment and was 52.85 mg/kg higher than control (P < 0.05); all of four organic materials increased soil available P, and those in the BF and KH treatments were significantly higher than in the BC and BR treatments, and were 13.21 mg/kg and 12.07 mg/kg higher than the control (P < 0.05), respectively. All the four organic materials significantly increased soil available K (P < 0.05), and that in KH treatment was significantly higher than those in the others, and was 136.00 mg/kg higher than control. Only the KH demonstrated significant increase of soil available Fe and that was 71.59 mg/kg higher than the control (P < 0.05), the BC significantly increased soil available Zn and that was 0.94 mg/kg higher than control, and no organic materials increased soil available Mn and Cu. 2) In limestone soil after incubation of 180 days, four organic materials did not improve the soil available N, but significantly increased soil available P (P < 0.05). The soil available P in the BF treatment was significantly higher than those in the other three ones (P < 0.05), and was 4.67 mg/kg higher than control (P < 0.05). The soil available K in the KH treatment was significantly higher than those in the other three ones (P < 0.05), and was 94.00 mg/kg higher than control (P < 0.05). Both the BF and the KH treatments significantly increased soil available Fe, and resulted in an increase of 190.61 mg/kg and 249.43 mg/kg than the control (P < 0.05) . The soil available Mn in the BF, KH and BC treatments were significantly increased by 135.74 mg/kg, 155.96 mg/kg and 51.51 mg/kg (P < 0.05), respectively. Soil available Cu in both the BF and the KH treatments were also significantly increased, and were 1.79 mg/kg and 2.99 mg/kg higher than the control. Available Zn was only significantly increased in the BR treatment, and was 3.23 mg/kg higher than the control (P < 0.05). 3) In red soil (pH 4.46), only BR increased soil pH, and reduced soil exchangeable Al³⁺ by 3.04 cmol/kg than the control (P < 0.05). By contrast, in limestone soil (pH 6.13), all the four organic materials significantly increased soil pH (P < 0.05), but did not greatly affect the exchangeable Al³⁺ content.

Conclusions  Different organic materials exhibit different regulatory roles in improving the soil fertility in Carya cathayensis forest lands with different yield levels. Application of organic materials improves soil nutrient supply in the forest soils with high-yielding, and could significantly increase soil available nutrients, soil pH, and reduce the toxicity of aluminum in the forest soils with a low-yielding.