Soil health indicators impacted by long-term cattle manure and inorganic fertilizer application in a corn-soybean rotation of South Dakota.

Manure impacts labile pools of soil organic carbon (SOC) and nitrogen (N) which can influence soil microbial composition (MCC) and enzyme activities, and hence soil health. The present study was conducted to investigate the impacts of long-term dairy manure and inorganic fertilizers (INF) on soil carbon (C) as well as nitrogen (N) fractions, enzyme activities, and microbial community structure in different time horizons at planting (P), one month after planting (1MAP), and after harvesting (H) under corn (Zea mays L.)-soybean (Glycine max L.) rotation. Study treatments included three manure application rates (low, phosphorus-based recommended rate; medium, nitrogen-based recommended rate; and high, the double rate of medium nitrogen based recommended rate), two INF rates (medium only nitrogen additions; and high nitrogen, phosphorus, potassium, zinc, and sulfur additions) and a control (no application of manure and/or inorganic fertilizer). In comparison to the INF, the dairy manure not only significantly increased chemical fractions of C and N but also impacted the enzyme activities. Average urease activity after manure was applied was shown to be 26.8% higher than it was with INF applied at planting. The ß-Glucosidase activity was 6 and 14% higher with manure than it was with INF at 1MAP and harvesting, respectively. The cold-water extractable nitrogen (CWEN) was enhanced with high manure rate at all timings of sampling compared to the high fertilizer rate (53%), and CK (90%). Principal component analysis indicated that MCC under manure differed from those under the INF treatments. The total bacteria/total fungi ratio at planting was increased with the INF compared to the manure addition. Pearson's correlation analysis showed that CWEC, CWEN, and enzyme activities especially ß-Glucosidase activity were the key determinants of MCC. Data from this study showed that, compared to inorganic fertilizers, manure can be beneficial in enhancing soil health indicators.

Analyzing the impacts of three types of biochar on soil carbon fractions and physiochemical properties in a corn-soybean rotation.

Biochar is a solid material obtained when biomass is thermochemically converted in an oxygen-limited environment. In most previous studies, the impacts of biochar on soil properties and organic carbon (C) were investigated under controlled conditions, mainly laboratory incubation or greenhouse studies. This 2-year field study was conducted to evaluate the influence of biochar on selected soil physical and chemical properties and carbon and nitrogen fractions for two selected soil types (clay loam and a sandy loam soil) under a corn (Zea mays L.)-soybean (Glycine max L.) rotation. The three plant based biochar materials used for this study were corn stover (CS), ponderosa pine (Pinus ponderosa Lawson and C. Lawson) wood residue (PW), and switchgrass (Panicum virgatum L.) (SG). Data showed that CS and SG significantly increased the pH of acidic soil at the eroded landscape position but produced no significant change in soil pH at the depositional landscape position. The effects of biochar treatments on cold water extractable C (WSC) and nitrogen (WSN) fractions for the 0-7.5 cm depth were depended on biochar and soil type. Results suggested that alkaline biochars applied at 10 Mg ha-1 can increase the pH and WSC fraction of acidic sandy loam soil, but the 10 Mg ha-1 rate might be low to substantially improve physical properties and hot water extractable C and N fractions of soil. Application of higher rates of biochar and long-term monitoring is needed to quantify the benefits of biochar under field conditions on soils in different environmental conditions.