Manure applications combined with chemical fertilizer improves crop yield and soil functionality

The current farming system is highly reliant on synthetic fertilizers,
which adversely affect soil quality, the environment, and crop production.
Improving crop productivity on a sustainable basis is a challenging issue
in the current agricultural system. To address this issue, we assumed that
the combined use of manure and chemical fertilizers (CF) could improve
rice grain yield and soil properties without the expense of the
environment. Therefore, a two-year field experiment was conducted to
explore optimal fertilizer management strategies using a combination of CF
and organic fertilizer in the form of cattle manure (CM) or poultry manure
(PM). Manure was added at two levels and soil microbial biomass
production, enzyme activities, nutrient content, as well as grain yield of
rice were measured. The study consisted of six treatments: no N fertilizer
control (Neg-Con); 100% chemical fertilizer (Pos-Con); 60% CM + 40% CF
(High-CM); 30% CM + 70% CF (Low-CM); 60% PM + 40% CF (High-PM), and 30% PM
+ 70% CF (Low-PM). Results showed that the addition of manure
significantly increased soil enzymatic activities such as soil invertase,
acid phosphatase, urease, catalase, ꞵ-glucosidase, and cellulase as
compared to sole chemical fertilizer application. Similarly, the combined
fertilizers application led to significant increases in soil microbial
biomass carbon (MBC), microbial biomass nitrogen (MBN), soil pH, soil
organic carbon (SOC), total nitrogen (TN), available nitrogen (AN),
available phosphorous (AP) and rice yield. Average increases in soil MBC,
MBN, SOC AN, and AP in the 0–20 cm soil depth were 62.2%, 54.5%, 29.2%,
17.4%, and 19.8%, respectively, across the years in the High-CM treatment
compared with the Pos-Con. In addition, the linear regression analysis
showed that soil enzymatic activities were highly positively correlated
with soil MBC and MBN. The PCA and linear regression analyses showed that
the increased soil enzyme activities and microbial biomass production
played a key role in the higher grain yield of rice. Overall, the results
of this study demonstrate that the combined use of synthetic fertilizer
and organic fertilizer in paddy fields could be beneficial for the farmers
in southern China by improving soil functionality and yield of rice on a
sustainable basis.