Biochar application to the soil can improve soil quality and nutrient leaching loss from swine manure adapted soils. Our working hypothesis was that the biochar-incubated with manure could be a better soil amendment than conventional manure application. The manure-biochar application to the soil would decrease nutrient leaching from manure and increase plant-available nutrients. The study objectives were to 1) assess the physicochemical properties of the manure-biochar mixture after lab incubation and 2) evaluate the impact of biochar-treated swine manure on soil total C, N, and other major and minor nutrients in comparison to conventional manure application to soil. Three biochars 1) neutral pH red-oak (RO), 2) highly alkaline autothermal corn (Zea mays) stover (HAP), and 3) mild acidic Fe-treated autothermal corn stover (HAPE) were incubated with swine manure for a month. The biochar-manure mixture was applied in triplicate to soil columns with an application rate determined by the P2O5-P content in manure or manure-biochar mixtures after the incubation. The ammonium (NH4+), nitrate (NO3‒), and reactive P concentrations in soil column leachates were recorded for eight leaching events. Soil properties and plant-available nutrients were compared between treatments and control manure and soil. Manure-(HAP&HAPE) biochar treatments significantly increased soil organic matter (OM), and all biochar-manure mixture increased (numerically) soil total C, N, and improved soil bulk density. Concentrations of NH4+ and NO3‒ significantly increased in MHAPE column leachates during this 4-week study and the KCl-extractable NH4+ and NO3‒ in the soil at the end of the experiment. A significant reduction in soil Mehlich3 Cu was also observed for the manure-HAPE mixture compared with the manure control. The manure-red oak biochar significantly increased the soil Mn availability than other manure-biochar treatments or manure control. Overall, the manure-biochar incubation enabled biochar to stabilize the C and several nutrients from manure. The subsequent manure-biochar mixture application to soil improved soil quality and plant nutrient availability compared to conventional manure application. This proof-of-the-concept study suggests that biochars could be used to solve both environmental and agronomic challenges and further improve the sustainability of animal and crop production agriculture.

The Conservation Reserve Program (CRP) is a U.S. federal land conservation program that incentivizes grassland reestablishment on marginal lands. Although this program has many environmental benefits, two critical questions remain: does reestablishing grasslands via CRP also result in soil health recovery, and what parts of restored fields (i.e., topographic positions) recover the fastest? We hypothesized that soil health will recover over time after converting cropland to CRP grassland and that recovery will be greatest at higher topographic positions. To test this, we sampled 241 midwestern U.S. soils along a grassland chronosequence (0-40 yr, including native grasslands) and at four topographic positions (i.e., a chronotoposequence). Soils were measured for bulk density, maximum water holding capacity (MWHC), soil organic C (SOC), extractable inorganic N, potentially mineralizable C (PMC), and N. Native grasslands had superior soil health compared with cropland and most CRP soils, and even 40 yr since grassland reestablishment was not adequate for full soil health recovery. Topographic position strongly influenced soil health indicators and often masked any CRP effect, especially with MWHC and SOC. However, PMC (a measure of active C) responded most rapidly to CRP and consistently across the landscape and was 26-34% greater 19-40 yr after grassland reestablishment. Reestablishing grasslands through CRP can improve soil health, although topographic position regulates the recovery, with greatest improvements at shoulder slope positions. Patience is needed to observe changes in soil health, even in response to a drastic management change like conversion of cropland to CRP grassland.

No abstract

Core Ideas Water filled porosity (WFP) controlled N dynamics in the drainfields. Sand layer was hotspot for nitrification due to 0.07–0.32 WFP. Soil layer was hotspot for denitrification due to 0.55–0.91 WFP. Organic N was mobile in the vadose zone and leached below drainfields. Onsite wastewater treatment systems (OWTS), commonly known as septic systems, are increasingly recognized as a potential source of nitrogen in the shallow groundwater. Our objective was to investigate the effect of hydrological and biogeochemical factors in the vadose zone on the fate of effluent‐borne N in the drainfields of a drip‐dispersal OWTS. Three lysimeters (152.4 cm long, 91.4 cm wide, and 91.4 cm high) were constructed using pressure‐treated wood to mimic OWTS drainfields. Each lysimeter had three distinct layers of gravel–sand mixture, soil, and commercial sand. A drip tube, which was covered with commercial sand before planting St. Augustine grass (Stenotaphrum Trin.) on the top and sides of the lysimeters, dispersed 9 L of septic tank effluent (STE) per day on top of the stacked layers. Each lysimeter was instrumented with 10 multi‐probe sensors to determine the water content, electrical conductivity (EC), and temperature in the center and sides of sand and soil layers. Leachate samples were collected over 67 events, which consisted of one sample every 24 h for 15 d (n = 15) and weekly flow‐weighted composite samples (n = 52). In all events, the pH, EC, and chloride were lower in the leachate than STE. Daily multi‐probe data showed that EC was greater in the center than sides of the lysimeters due to more STE interaction. Sensor water content data were used to calculate water filled porosity (WFP), which was greater in the soil (0.55–0.9) than sand (0.07–0.32) due to the textural differences. Mean total N was 70 mg L−1 in the STE, which reduced to 27.4 mg L−1 in the leachate likely due to the denitrification in the soil layer. The dominance of NOx–N in the leachate (61%) as compared to STE (0.6%) was attributed to the nitrification in the sand layer. Higher proportion of organic N in the leachate (39%) than STE (16%) suggests that organic N was mobile in the vadose zone and leached below the drainfields. We conclude that hydrological and biogeochemical controls in the vadose zone play an important role in N transformations and transport of NOx–N and organic N below OWTS drainfields.

Biochar application to the soil can improve soil quality and nutrient leaching loss. Recent studies have reported that surficial application of biochar to stored swine manure can reduce emissions of odorous compounds and reduce the volatilization loss of ammonia. Our working hypothesis was that the biochar-treated manure application to the soil would decrease nutrient leaching from manure and increase plant-available nutrients. The study objectives were to evaluate the impact of biochar-treated swine manure on soil total C, N, and other major and minor nutrients. Three biochars (i) neutral pH red-oak (RO), (ii) highly alkaline autothermal corn (Zea mays) stover (HAP), and (iii) mild acidic Fe-treated autothermal corn stover (HAPE) were incubated with swine manure for a month. The biochar-manure mixture was applied in triplicate to soil columns with application rate determined by the P2O5-P content in manure or manure-biochar mixtures after the incubation. The ammonium (NH4+), nitrate (NO3-), and reactive P concentrations in soil column leachates were recorded for eight leaching events. Soil properties and plant-available nutrients were compared between treatments and control manure & soil. Manure-(HAP&HAPE) biochar treatments significantly increased soil organic matter (OM) and increased soil total C, N, and improved soil bulk density. Concentrations of KCl-extractable NH4+ and NO3- significantly increased in HAPE column leachates during this 4-week study and in the soil after the experiment. A significant reduction in soil Mehlich3 Cu was also observed for the manure-HAPE mixture compared with the control. Overall, the manure-biochar incubation enabled biochar to sorb nutrients from manure, and the subsequent manure-biochar mixture application to soil improved soil quality and plant nutrient availability in comparison to conventional manure application to soil. This proof-of-the-concept study suggests that biochars could be used to solve both environmental and agronomic challenges and further improve the sustainability of animal and crop production agriculture.

Biochar application to the soil can improve soil quality and nutrient leaching loss. Recent studies have reported that surficial application of biochar to stored swine manure can reduce emissions of odorous compounds and reduce the volatilization loss of ammonia. Our working hypothesis was that the biochar-treated manure application to the soil would decrease nutrient leaching from manure and increase plant-available nutrients. The study objectives were to evaluate the impact of biochar-treated swine manure on soil total C, N, and other major and minor nutrients. Three biochars (i) neutral pH red-oak (RO), (ii) highly alkaline autothermal corn (Zea mays) stover (HAP), and (iii) mild acidic Fe-treated autothermal corn stover (HAPE) were incubated with swine manure for a month. The biochar-manure mixture was applied in triplicate to soil columns with application rate determined by the P2O5-P content in manure or manure-biochar mixtures after the incubation. The ammonium (NH4+), nitrate (NO3-), and reactive P concentrations in soil column leachates were recorded for eight leaching events. Soil properties and plant-available nutrients were compared between treatments and control manure & soil. Manure-(HAP&HAPE) biochar treatments significantly increased soil organic matter (OM) and increased soil total C, N, and improved soil bulk density. Concentrations of KCl-extractable NH4+ and NO3- significantly increased in HAPE column leachates during this 4-week study and in the soil after the experiment. A significant reduction in soil Mehlich3 Cu was also observed for the manure-HAPE mixture compared with the control. Overall, the manure-biochar incubation enabled biochar to sorb nutrients from manure, and the subsequent manure-biochar mixture application to soil improved soil quality and plant nutrient availability in comparison to conventional manure application to soil. This proof-of-the-concept study suggests that biochars could be used to solve both environmental and agronomic challenges and further improve the sustainability of animal and crop production agriculture.

Maize (Zea mays L.) stover can be harvested for multiple uses or left in the field to sustain soil organic carbon (SOC), cycle essential plant nutrients, and protect soil health. This 13-year field study quantified effects of no (0 Mg ha -1 y -1 ), low (1.0 to 1.4 Mg ha -1 y -1 ), moderate (3.5 to 4.0 Mg ha -1 y -1 ), or high rates (4.7 to 5.4 Mg ha -1 y -1 ) of stover harvest from either continuous maize or maizesoybean [Glycine max. (L.) Merr.] rotation on grain yield, plant nutrient concentrations, and multiple soil properties at two sites in Iowa, USA. Stover harvest increased plant macro-and micro-nutrient removal, but did not affect average grain yields of either crops. Soil inorganic carbon (IC), SOC, bulk density, pH, and cation exchange capacity (CEC) showed no significant differences due to stover harvest. Plant tissue and soil-test nutrient concentration effects were also minor and site-specific.Stover harvest significantly (p<0.05) decreased exchangeable K and Ca concentrations by 8.3 to 23.8% and 0.3 to 22.5% but overall soil health indicator effects were minimal. Overall, based on crop yields, plant nutrient and soil-test concentrations, soil health indicators, and carbon sequestration estimates, maize stover harvest can be sustainable provided: (i) grain yields consistently exceed 11 Mg ha -1 , (ii) stover removal does not exceed 40% of the above-ground biomass (i.e., 3.5 to 4.0 Mg ha -1 y -1 ), and (iii) plant nutrients (especially K) are closely monitored.

Loss of nitrate-nitrogen (NO 3 À -N) from Midwestern U.S. agricultural fields can impair water quality and be an economic loss to farmers. Winter cover crops have shown promise as a remedy, but low adoption illustrates the need for alternatives. Here, we tested whether adding a carbon (C)-rich soil amendment (i.e., crude glycerol, a biodiesel byproduct) can increase soil microbial biomass (MB) and promote N immobilisation under various conditions and then determined whether and when immobilised N would be released. We conducted a laboratory incubation with a full factorial combination of four glycerol rates (0, +117, +468 and +1872 mg C kg À1 soil), three supplemental NO 3 À -N rates (0, +10 and +40 mg N kg À1 ) and two soils (Clarion clay loam and Sparta loamy sand). Soil inorganic N (NH 4 + -N and NO 3 À -N) and MB were measured at seven and three time points, respectively, across the 98 days incubation period. Across all treatments, glycerol increased MBN in both short term (7 days; 4%-1137% compared to no glycerol addition) and long term (98 days; 10%-169%) and decreased NO 3 À -N with increasing rate of glycerol.Adding glycerol caused net N immobilisation of 21%-61% (+117 mg C kg À1 addition) and $100% (+468 and +1872 mg C kg À1 addition) compared to the control. Some of that immobilised inorganic N was likely released through MB turnover, but timing and rate of release depended on the soil and added N rate.Adding 40 mg N kg À1 with no glycerol showed nearly twice the net N mineralisation rate than with the low or no applied Nproviding evidence for soil N priming. Overall, glycerol has the potential for use as a soil amendment to increase MB and temporarily immobilise NO 3 À -N and then make some of that N crop available through MB turnover. Highlights• Crude glycerol, a biodiesel by-product, was evaluated as a soil amendment to reduce soil nitrate. • Glycerol strongly increased soil microbial biomass and decreased nitrate under all conditions.