Effects of different fertilization patterns on microbial biomass carbon and nitrogen in greenhouse vegetable soil

Objectives A fixed-site greenhouse vegetable fertilization experiment has been carried out with rotation of tomato in spring season and celery in autumn-winter season in Tianjin city since 2009. The effects of different fertilization patterns on soil microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were investigated in order to provide a scientific fertilization basis for sustainable and high-efficient vegetable production in greenhouse.

Methods The experiment comprises eight treatments: 1) No nitrogen input (No N); 2) Complete chemical nitrogen fertilizer (4/4CN); 3) 3/4 N from chemical fertilizer, 1/4 from pig manure (3/4CN + 1/4PN); 4) 2/4 N from chemical fertilizer, 2/4 from pig manure (2/4CN + 2/4PN); 5) 1/4 N from chemical fertilizer, 3/4 from pig manure (1/4CN + 3/4PN); 6) 2/4 N from chemical fertilizer, 1/4 from pig manure and 1/4 from straw (2/4CN + 1/4PN + 1/4SN); 7) 2/4 N from chemical fertilizer, 2/4 from straw (2/4CN + 2/4SN); and 8) Conventional fertilization (CF). Except for No nitrogen and CF treatments, all the treatments were applied with the same amounts of N, P₂O₅ and K₂O nutrients, but varied proportion of nitrogen from different sources. Until this investigation, it was the ninth harvest for autumn-winter season celery and the tenth harvest for spring season tomato. 0–20 cm surface soil samples were collected, the soil MBC and MBN contents were measured at different growth stages of celery and tomato growing seasons, and their correlations with vegetable yields were analyzed.

Results 1) Soil MBC and MBN contents in different treatments increased first and then decreased during the studied periods. The relatively higher values for soil MBC and MBN contents respectively appeared at 90 and 60 days after transplanting of celery, and at 20–80 days for soil MBC and 60 days for soil MBN after transplanting of tomato. 2) In the celery season when it was in autumn-winter, the soil MBC and MBN contents were respectively 185.0–514.6 and 34.3–79.1 mg/kg, with increases of 15.1%–81.7% and 24.5%–100.0% in treatments of combined application of manure and/or straw with chemical fertilizers, compared to the 4/4CN treatment, and the highest increases for the contents of MBC and MBN in straw-incorporated treatments were 62.0%–81.7% and 81.1%–100.0%, respectively. In the tomato season when it was in spring, the soil MBC and MBN contents in the combined application of manure and/or straw with chemical fertilizers were respectively 120.7–338.0 and 25.5–68.8 mg/kg, with increases of 16.9%–86.9% and 12.2%–109.3%, compared to the 4/4 CN treatment, and the highest increase values in straw-applied treatments were 61.4%–86.9% and 78.2%–109.3%, respectively. 3) Significant correlation relationships were found between the soil MBC, MBN contents and the corresponding vegetable yield of current season and total yield since the start of the experiment.

Conclusions Under the same input of nutrients, the increase effects in soil MBC, MBN contents are significantly higher in the fertilization patterns of combined application of manure and/or straw with chemical fertilizers. Soil MBC, MBN contents are positively and significantly correlated with the growing season and the total greenhouse vegetable yields. Therefore, the combined use of organic and inorganic fertilizers is capable of increasing the soil MBC, MBN contents and keeping the soil fertility and sustainability in greenhouse vegetable production.