Long-Term Nitrogen Addition Decreases Soil Carbon Mineralization in an N-Rich Primary Tropical Forest

Anthropogenic elevated nitrogen (N) deposition has an accelerated terrestrial N cycle, shaping soil carbon dynamics and storage through altering soil organic carbon mineralization processes. However, it remains unclear how long-term high N deposition affects soil carbon mineralization in tropical forests. To address this question, we established a long-term N deposition experiment in an N-rich lowland tropical forest of Southern China with N additions such as NH4NO3 of 0 (Control), 50 (Low-N), 100 (Medium-N) and 150 (High-N) kg N ha−1 yr−1, and laboratory incubation experiment, used to explore the response of soil carbon mineralization to the N additions therein. The results showed that 15 years of N additions significantly decreased soil carbon mineralization rates. During the incubation period from the 14th day to 56th day, the average decreases in soil CO2 emission rates were 18%, 33% and 47% in the low-N, medium-N and high-N treatments, respectively, compared with the Control. These negative effects were primarily aroused by the reduced soil microbial biomass and modified microbial functions (e.g., a decrease in bacteria relative abundance), which could be attributed to N-addition-induced soil acidification and potential phosphorus limitation in this forest. We further found that N additions greatly increased soil-dissolved organic carbon (DOC), and there were significantly negative relationships between microbial biomass and soil DOC, indicating that microbial consumption on soil-soluble carbon pool may decrease. These results suggests that long-term N deposition can increase soil carbon stability and benefit carbon sequestration through decreased carbon mineralization in N-rich tropical forests. This study can help us understand how microbes control soil carbon cycling and carbon sink in the tropics under both elevated N deposition and carbon dioxide in the future.

Higher Biochar Rate Can Be Efficient in Reducing Nitrogen Mineralization and Nitrification in the Excessive Compost-Fertilized Soils

The effects of a high biochar rate on soil carbon mineralization, when co-applied with excessive compost, have been reported in previous studies, but there is a dearth of studies focusing on soil nitrogen. In order to ascertain the positive or snegative effects of a higher biochar rate on excessive compost, compost (5 wt. %) and three slow pyrolysis (>700 °C) biochars (formosan ash (Fraxinus formosana Hayata), ash biochar; makino bamboo (Phyllostachys makino Hayata), bamboo biochar; and lead tree (Leucaena leucocephala (Lam.) de. Wit), lead tree biochar) were applied (0, 2 and 5 wt. %) to three soils (one Oxisols and two Inceptisols). Destructive sampling occurred at 1, 3, 7, 28, 56, 84, 140, 196, 294, and 400 days to monitor for changes in soil chemistry. The overall results showed that, compared to the other rates, the 5% biochar application rate significantly reduced the concentrations of inorganic N (NO3−-N + NH4+-N) in the following, decreasing order: lead tree biochar > bamboo biochar > ash biochar. The soil response in terms of ammonium and nitrate followed a similar declining trend in the three soils throughout the incubation periods, with this effect increasing in tandem with the biochar application rate. Over time, the soil NO3−-N increased, probably due to the excessive compost N mineralization; however, the levels of soil NO3−-N in the sample undergoing the 5% biochar application rate remained the lowest, to a significant degree. The soils’ original properties determined the degree of ammonium and nitrate reduction after biochar addition. To reduce soil NO3−-N pollution and increase the efficiency of compost fertilizer use, a high rate of biochar application (especially with that pyrolyzed at high temperatures (>700 °C)) to excessively compost-fertilized soils is highly recommended.

Comparison of nonlinear models for the description of carbon mineralization in soils treated with pig slurry

One of the strategies to reduce environmental impacts caused by pig slurry is its application to soils for agricultural productions. Carbon mineralization curves can be used to determine the best periods for the use of organic matter for an adequate management of soils and growing plants. The objective of this study was to evaluate the fit of nonlinear models for soil carbon mineralization. The experiment was conducted using a randomized block design with four replications and four treatments. The treatments consisted of monthly applications of pig slurry at rates of 0, 7.5, 15.0, and 30.0 m3 ha-1 ofpig slurry. Soil samples were collected and incubated for 26 days; then, seven observations of mineralized carbon volume were made over time. The description of the carbon mineralization followed the Stanford and Smith, Cabrera, and Juma models, considering the structure of autoregressive errors AR (1), when necessary; the fits were compared using the Akaike Information Criterion (AIC). The description of carbon mineralization in the treatments by nonlinear models was, in general, adequate. Juma was the most adequate model to describe the treatment with rate of 0. Stanford and Smith was the most adequate model to describe the treatments with rates of 7.5 and 15.0 m3 ha-1. Cabrera was the most adequate model to describe the treatment with rate of 30.0 m3 ha-1.

Changes in Some Soil Chemical and Biological Properties on the Growing Season of Sesame in Çukurova Region

In present study, some soil characteristics of Sesamum indicum L. (Sesame) and its adjacent blank field (control) were compared in a growing season as pre (PreC and PreS) and post (PostC and PostS) harvest in Adana, Turkey. Soil macro (C, N, P and K) and micronutrients (Cu, Zn, Mn and Fe), carbon (Cmin) and nitrogen mineralizations and soil aerobic bacteria and fungi counts were determined in before and after harvest soils. Soils were humidified at 80% of their field capacity and then monitored for 45 days at 28 °C to determine soil carbon (Cmin) and nitrogen (Nmin) mineralization. Generally, macro and micronutrients (Cu, Zn, Mn and Fe) were higher in control than sesame field except phosphorus (P2O5) and there were found significant differences between them before and after harvest. Aerobic bacteria and fungi populations were decreased after harvest while fungi populations were increased in sesame soils compared to control. Soil CO2-C evolution was higher in sesame field than control. Rates of carbon mineralization was in order as following PostC < PreC < PostS< PreS. Rate of Nmin was significantly higher in sesame soils before harvest but it was lower after harvest compared to control. Carbon mineralization rates in sesame grown soils were significantly decreased and it was in order as following PostC < PreC < PostS < PreS. Decrease in soil carbon mineralization after harvest can be explained with decrease in soil microbial populations in short term.