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Estimating soil nitrogen (N) availability is important for developing effective N fertilizer recommendations for plant growth. We examined the ability of various soil biological properties to predict soil N availability, and plant dry matter and N uptake in two greenhouse trials with sorghum-sudangrass (Sorghum bicolor (L.) Moench ssp. Drummondii) as test crop using soils (0–10 cm) from 57 tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) pastures mostly in North Carolina and Virginia. Soil biological properties, the flush of CO2, cumulative carbon (C) mineralization, soil microbial biomass C, basal soil respiration, and plant available N were positively correlated with net N mineralization, plant dry matter, and N uptake in both the greenhouse trials. The flush of CO2, which is the measure of carbon dioxide released from dried and rewetted soil during the first 3 days of aerobic incubation, explained 77% and 72% of the variation in the plant N uptake in Greenhouse Trial 1 and 2, respectively. Total soil N and residual inorganic N in both trials and manganese in Trial 1 and particulate organic C in Trial 2 added minor contributions to explaining variation in plant N uptake. The flush of CO2 was reflective of management history and soil texture. We conclude that the flush of CO2 is a reliable predictor of soil N availability across diverse pasture soils because (a) it was highly correlated with net N mineralization, plant dry matter, and N uptake, and (b) it was less laborious and more cost-effective than other direct indicators of soil N availability. [ABSTRACT FROM AUTHOR]

Estimating soil nitrogen (N) availability is important for developing effective N fertilizer recommendations for plant growth. We examined the ability of various soil biological properties to predict soil N availability, and plant dry matter and N uptake in two greenhouse trials with sorghum-sudangrass (Sorghum bicolor (L.) Moench ssp. Drummondii) as test crop using soils (0–10 cm) from 57 tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) pastures mostly in North Carolina and Virginia. Soil biological properties, the flush of CO2, cumulative carbon (C) mineralization, soil microbial biomass C, basal soil respiration, and plant available N were positively correlated with net N mineralization, plant dry matter, and N uptake in both the greenhouse trials. The flush of CO2, which is the measure of carbon dioxide released from dried and rewetted soil during the first 3 days of aerobic incubation, explained 77% and 72% of the variation in the plant N uptake in Greenhouse Trial 1 and 2, respectively. Total soil N and residual inorganic N in both trials and manganese in Trial 1 and particulate organic C in Trial 2 added minor contributions to explaining variation in plant N uptake. The flush of CO2 was reflective of management history and soil texture. We conclude that the flush of CO2 is a reliable predictor of soil N availability across diverse pasture soils because (a) it was highly correlated with net N mineralization, plant dry matter, and N uptake, and (b) it was less laborious and more cost-effective than other direct indicators of soil N availability. [ABSTRACT FROM AUTHOR]

Aims: Cover crop species selection for soybean (Glycine max) production under no-tillage (NT) management may affect soil organic C sequestration by altering the quantity and quality of C inputs, thereby affecting cropping system sustainability. If so, the underlying mechanisms for such regulation are still unclear. Methods: We assessed changes in soil C and N fractions at 0-0.1 m depth and soil C stock at 0-0.6 m depth during the last three years of dry-season cover cropping in a soybean production system managed with NT for 9 years on a Rhodic Hapludox in Sao Paulo, Brazil. Dry-season management treatments were repeated yearly in a split-plot scheme. Main plots during the fall-winter were (1) ruzigrass (Urochloa ruziziensis), (2) grain sorghum (Sorghum bicolor), and (3) the intercropping of ruzigrass and sorghum. Subplots during spring prior to planting soybean were (a) pearl millet (Pennisetum glaucum), (b) sunn hemp (Crotalaria juncea), and (c) forage sorghum (Sorghum bicolor). Results: Soil C and N fractions were affected according to crop residue characteristics of the rotations. Higher soil C stocks in 2012 and 2015 (7 % an average) were observed at 0.2–0.4 m depth by ruzigrass compared to sorghum. High crop residue input with ruzigrass in the fall-winter sequestered 0.61 Mg C ha− 1 yr− 1 at 0-0.1 m soil depth compared with lower C sequestration using grain sorghum (0.29 Mg C ha− 1 yr− 1). Conclusions: The quantity and quality of crop residues impact its retention on soil surface controlling the dynamics of soil C and N fractions and can be considered relevant for soil C sequestration. These aspects could contribute to the mitigation of atmospheric CO2 in crop production systems. [ABSTRACT FROM AUTHOR]

In tropical integrated crop-livestock under no-till (NT) systems, the surface application/reapplication of lime and/or gypsum can reduce re-acidification rate of the soil and improve plant nutrition, crop yields, and profitability. This study was conducted in the Brazilian Cerrado, which has dry winters, and aimed to evaluate the effects of surface application/reapplication of lime and/or gypsum on soil improvement, plant nutrition and crop yield improvement, as well as the forage dry matter (DM) yield, estimated meat production, and economic results. The crop rotation used between November 2004 and August 2008 was as follows: peanut (Arachis hypogaea) and white oat (Avena sativa) cultivated alone (on the first and second spring/summer and autumn/winter, respectively) and corn (Zea mays) intercropped with palisade grass [Urochloa brizantha cv. 'Marandu'] and pasture (on the third and fourth spring/summer and autumn/winter, respectively). The experimental design was a randomized block with four replications. The treatments consisted of natural conditions of a sandy clay loam kaolinitic and thermic Typic Haplorthox (control) and the surface application of lime and/or gypsum in October 2002 and reapplication in November 2004. Surface liming was an efficient practice for increasing pH and reducing the exchangeable acidity (H + Al) and concentration of Al extending to a depth of 0.60 m. Gypsum application increased Ca2+ levels through the soil profile. Liming (with or without gypsum) had a positive effect on the nutrient acquisition by peanut, white oat, and corn crops, producing on average 48%, 52%, and 61% more pod and grain yield, respectively, than that obtained in the absence of soil amendments and with gypsum alone. The surface application of lime + gypsum also promoted forage DM yield of corn-palisade grass intercropping 22% higher than lime application and 164% higher than control; estimated meat production 26% higher than lime application and 225% higher than control, and increased economic results during four growing seasons. The surface application of lime + gypsum is an essential tool for food production in NT tropical agriculture with high soil acidity. [ABSTRACT FROM AUTHOR]

Urochloa spp. grow vigorously in the dry-season of the tropics, and have been used successfully to provide abundant surface residue as cover crop for no-till soybean (Glycine max). Nitrogen (N) fertilizer application could enhance cover crop biomass production and its ground cover and accelerate residue decomposition, but how these cascading factors affect nutrient availability to the subsequent soybean crop is not known. We evaluated nutrient cycling and soybean nutrition and yield components following different timings of N application to living and desiccated Urochloa cover crops. The experiment was conducted in two growing seasons at Botucatu, São Paulo State, Brazil. Treatments consisted of two cover crop grasses (Urochloa brizantha and Urochloa ruziziensis) and six N management systems [control (no N application); N application at soybean sowing (40 kg N ha−1) plus topdressing (60 kg N ha−1 at V5 stage); N application 20 days before desiccation (DBD) of cover crops, N application 10 DBD; N application 5 DBD; and N application 1 day before sowing of soybean, using the rate of 100 kg N ha−1 in the latter four treatments]. Both cover crops produced high amount of shoot biomass (> 9.7 Mg ha−1), but U. brizantha was 48% more productive than U. ruziziensis. Nutrient accumulation in cover crop straw was enhanced due to greater biomass production in treatments with N applied 20 and 10 DBD. Soybean grain yield was 17% greater following U. brizantha than following U. ruziziensis. Nitrogen application at different times did not affect soybean grain yield. These results suggest that Urochloa biomass, macronutrient accumulation, and subsequent release rates can be enhanced with N application, but it had little short-term impact on soybean yield components. [ABSTRACT FROM AUTHOR]

Large-scale biochar field trials have been conducted worldwide to test for "carbon negative strategy" in the event of carbon credit and if other subsidies become enacted in the future. Once amended to the soil, biochar engages in complex organo-mineral interactions, fragmentation, transport, and other aging mechanisms exhibiting interactions with treatments including the irrigation and fertilizer application. As a result, quantitative tracing of biochar carbon relying on the routinely measured soil parameters, e.g., total/particulate organic carbon, poses a significant analytical uncertainty. This study utilized two biochar field trial sites to calibrate for the biochar carbon structure and quantity based on the infrared- and fluorescence-based chemometrics: (1) slow pyrolysis biochar pellets on kaolinitic Greenville fine sandy loam in Georgia and (2) fast pyrolysis biochar powder on Crider silt loam in Kentucky. Partial least squares-based calibration was constructed to predict the amount of solvent (toluene/methanol)-extractable fluorescence fingerprint (290/350 nm excitation and emission peak) attributed to biochar based on the comparison with the authentic standard. Near-infrared-based detection was sensitive to the C-H and C-C bands, as a function of biochar loading and the particulate organic carbon content (< 53 μm) of the bulk soil. Developed chemometrics could be used to validate tarry carbon structures intrinsic to biochar additives, as the impact of biochar additives on soil chemical properties (pH, electric conductivity, and dissolved organic carbon) becomes attenuated over time. [ABSTRACT FROM AUTHOR]