Partial substitution of
inorganic fertilizers with organic amendments is an important agricultural
management practice. An 11-year field
experiment (22 cropping periods) was carried out to analyze the impacts of
different partial substitution treatments on crop yields and the transformation
of nitrogen fractions in greenhouse vegetable soil. Four treatments with equal N, P2O5,
and K2O inputs were selected, including complete inorganic
fertilizer N (CN), 50% inorganic fertilizer N plus 50% pig manure N (CPN), 50%
inorganic fertilizer N plus 25% pig manure N and 25% corn straw N (CPSN), and
50% inorganic fertilizer N plus 50% corn straw N (CSN). Organic substitution treatments tended to
increase crop yields since the 6th cropping period compared to the CN
treatment. From the 8th to the 22nd
cropping periods, the highest yields were observed in the CPSN treatment where
yields were 7.5–11.1% greater than in CN treatment. After 11-year fertilization, compared to CN,
organic substitution treatments significantly increased the concentrations of
NO3–-N, NH4+-N, acid hydrolysis
ammonium-N (AHAN), amino acid-N (AAN), amino sugar-N (ASN), and acid hydrolysis
unknown-N (AHUN) in soil by 45.0–69.4, 32.8–58.1, 49.3–66.6, 62.0–69.5,
34.5–100.3, and 109.2–172.9%, respectively.
Redundancy analysis indicated that soil C/N and OC concentration
significantly affected the distribution of N fractions. The highest concentrations of NO3–-N,
AHAN, AAN, AHUN were found in the CPSN treatment. Organic substitution treatments increased the
activities of β-glucosidase, β-cellobiosidase, N-acetyl-glucosamidase,
L-aminopeptidase, and phosphatase in the soil.
Organic substitution treatments reduced vector length and increased
vector angle, indicating alleviation of constraints of C and N on soil
microorganisms. Organic substitution
treatments increased the total concentrations of phospholipid fatty acids
(PLFAs) in the soil by 109.9–205.3%, and increased the relative abundance of G+ bacteria and fungi taxa, but decreased the relative abundance of G– bacteria, total bacteria, and actinomycetes.
Overall, long-term organic substitution management increased soil OC concentration,
C/N, and the microbial population, the latter in turn positively influenced
soil enzyme activity. Enhanced
microorganism numbers and enzyme activity enhanced soil N sequestration by
transforming inorganic N to acid hydrolysis-N (AHN), and enhanced soil N supply
capacity by activating non-acid hydrolysis-N (NAHN) to AHN, thus improving
vegetable yield. Application of
inorganic fertilizer, manure, and straw was a more effective fertilization
model for achieving sustainable greenhouse vegetable production than
application of inorganic fertilizer alone.
