Proceedings - Soil Science Society of America最新文献

Soil carbon (C) is important to support sustainable agriculture, affect global C cycling, and influence the climate system. Manure fertilization is an important and widely used practice to increase agricultural productivity and soil organic carbon (SOC) pools, whereas its effect on soil inorganic carbon (SIC) and total C in deep soils is not reported. This knowledge gap restricts our ability to accurately evaluate C budget in agricultural soils because SIC in deep soils accounts for more than half of the global soil C pools, while current earth system models rarely take them into account. Herein, we examined changes of soil C along 0- to 3.0-m depth after 35 years of application of manure in a dryland agricultural ecosystem. We also measured C concentrations in soil samples (0–0.2 m) from 1985 to 2019 to evaluate C dynamics in topsoils. The objective was to understand how SIC and SOC in deep soils respond to manure fertilization in semiarid ecosystem, where SIC accounts for a large fraction of total C. We showed a divergent effect of 35 years of manure application on SOC and SIC in 0–3.0 m soil from a dryland agricultural ecosystem. Either within or across the two cropping systems examined, manure increased SOC in top 0.8 m layer but decreased SIC in 0.8–3.0 m layer, which offset SOC increase and resulted in 63.8 Mg ha⁻¹ decrease of total C in 0–3.0 m soil layer. Given the importance of soil C for sustainable agriculture and that drylands contain 80% of the global SIC and ∼50% of world cropland, immediate attention should be paid to such divergent effects in both mechanisms understanding and model prediction.

Currently barrens communities only represent about 1% of their original area in the Great Lakes region. To maintain or restore barrens vegetation, prescribed fire is often applied to limit the regeneration of undesirable species and shrubs. Vegetation community response is a combination of direct fire effects on the vegetation vitality and the indirect effect of soil nitrogen (N) loss that favors nutrient-poor adapted barren communities. In this study, we assessed forest floor and upper mineral soil (0–5 cm) pools of carbon (C), N, and mercury (Hg) before and after prescribed fire of the Moquah Barrens in northwest Wisconsin. Although we took measurements in four distinct cover types, we found no relationship between cover type and soil pools. Across all cover types, prescribed fire led to considerable emissions of C, N, and Hg in the forest floor but only Hg in the upper mineral soils (0–5 cm), presumably because maximum fire temperatures were met for Hg volatilization. We classified fire severity and soil surface temperatures at the quadrat scale, but no discernable relationships with emissions were observed. The lack of detectable relationships is likely the result of a mismatch between the scales of response variables and predictors. As a result, we calculated ecosystem-scale fire emissions based on the total area burned because we could not discern other smaller scale predictors. Overall emissions from dormant, spring season prescribed fires at the Moquah Barrens were approximately 11,000 Mg (5.5 Mg ha⁻¹) for C, 350 Mg for N (0.17 Mg ha⁻¹), and 4,500 g for Hg (2.3 g ha⁻¹).

There has been an ongoing discussion about whether using functionalized biochar nanoparticles for pollutant removal is practical. The existing uncertainty surrounding functionalized biochar nanoparticles raises questions regarding their effectiveness in unraveling this problem. In this study, functionalized biochar nanoparticles were produced from corn (Zea mays L.) residues and Conocarpus erectus L. wood at 400°C and 700°C using the H₂SO₄/HNO₃ treatment. The synthesized nanoparticles were used to explore their sorption properties for Pb²⁺. Various adsorption kinetic and isotherm models were evaluated using linear and nonlinear regression techniques. The functionalized biochar nanoparticles originated from wood at 400°C had the largest (80.74 mg g⁻¹) Pb²⁺ adsorption capacity due to their highest O/C and the most negative zeta potential. In comparison, nanoparticles fabricated from corn residues at 700°C showed the lowest (70.47 mg g⁻¹) Pb²⁺ adsorption capacity. Pyrolysis temperature affected the sorption process. Functionalized biochar nanoparticles produced at 400°C were more successful in sorbing the pollutant than those fabricated at 700°C. Linear and nonlinear pseudo-second-order kinetic models described Pb²⁺ adsorption kinetics well, indicating the rate-controlling step. The nonlinear Freundlich model described the equilibrium relationship between adsorbate concentration and capacity, elucidating adsorption site heterogeneity and biochar nanoparticles' affinity for Pb²⁺. Our study shows that functionalized biochar nanoparticles could help develop procedures for remediating polluted environments.

Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] is the predominant forest plantation species in the Pacific Northwest (PNW), with site productivity and fertilizer response influenced by climate and soil variations. This study investigates the utility of in situ 12-week supply measurements of nitrogen (N), calcium (Ca), and phosphorus (P) to ion-exchange resins (specifically Plant Root Simulator [PRS] probes) to estimate carbon (C):N ratios, soil nutrient contents (0–1 m), foliar nutrient concentrations, Douglas-fir productivity (site index and basal area mean annual increment), and fertilizer volume response. PRS nutrient supply rates were correlated with N, Ca, and P soil nutrient contents (0–1 m), C:N ratios, and foliar nutrient concentrations. Low PRS NO₃ supply rates (<25 mg N·m⁻²·burial period⁻¹) were correlated with lower Douglas-fir productivity and greater fertilizer volume response. PRS NO₃ supply rates performed as well as total soil N contents and foliar N concentrations at estimating volume growth response to fertilizer. Twelve weeks after fertilization, PRS NO₃, NH₄, and Ca supply rates were significantly elevated compared to the unfertilized treatment. This research found that PRS probes were an effective in situ tool and are recommended for understanding N, Ca, and P nutrient availabilities, site productivity, and fertilizer response in Douglas-fir plantations and for developing fertilizer prescriptions.

Phosphorus (P) recovery from waste streams can increase food system P use efficiency while simultaneousl mitigating point source P losses. Phytin is a P-rich waste product generated from maize grain biorefineries, largely located in the US Midwest. However, since the majority of P in phytin is organic, phytin-P is likely to have limited crop availability in soil following application, as it must first be mineralized to orthophosphate-P by soil phosphatases. To evaluate the fertilizer potential of phytin recovered from a maize wet milling plant and test hypothesized mechanisms of P mineralization, a five-step gradient of phytin substitution for monoammonium phosphate (MAP) (0%, 25%, 50%, 75%, and 100% substitution) was evaluated for maize (Zea mays L.) and soybean (Glycine max L.) growth in a P-deficient Aquic Argiudoll. Irrespective of crop species, aboveground biomass at end of vegetative growth (VT stage) was similar for up to 75% phytin substitution as MAP, but was 21% lower for maize and 49% for soybean when phytin was fully substituted for MAP. Soil microbial biomass carbon (C), nitrogen (N), and P, as well as activities of phosphomonoesterase and phosphodiesterase were invariant across the phytin substitution gradient, suggesting negligible mineralization of phytin P. Full substitution of MAP with phytin lowered soil microbial biomass C:N by 121% for maize and by 153% for soybean, and soil phosphatase activities per unit microbial biomass C were 24% higher under soybean. Our results indicate that phytin can be partially substituted for highly water-soluble P fertilizers for the two major crop species of the US Midwest in which phytin waste generation is co-located.

The degradation of soil quality in intensive cropping systems demands urgent attention to preserve soil health and sustain crop productivity. A 2-year field experiment conducted in the loamy sand soil of Gujarat's Plains and Hills explored integrated nutrient management (INM) effects on nutrient dynamics, soil attributes, and microbial populations in maize (Zea mays L.)–sesame (Sesamum indicum L.) cropping. Using a randomized block design with three replications and 12 treatments, notable enhancements in soil physical conditions were observed following the integrated application of organic manure and inorganic fertilizers. Specifically, the application of 75% recommended dose of fertilizer (RDF) and 25% recommended dose of nutrient (RDN) through vermicompost, added with an NPK consortium via soil application, significantly increased N, P, and K uptake in the maize crop as compared with other treatments. The application of 75% RDF and 25% RDN through farmyard manure, added with an NPK consortium via soil application, led to a substantial increase of organic carbon levels and nitrogen availability in the soil post-maize and sesame harvests, as well as with a marked increase in soil microbial populations. Correlation analysis representing the degree of association among all the traits underscores the potential of INM strategies to mitigate soil quality degradation and enhance nutrient cycling within maize–sesame cropping systems, thereby promoting agricultural sustainability in this specific agro-climatic region.

Nitrogen (N) depolymerization and mineralization in soils are catalyzed by extracellular enzymes, notably proteolytic and chitinolytic enzymes. However, there is limited knowledge of pH optima of these N-hydrolytic soil enzymes, potentially missing insights to soil pH effects on N cycling and requiring assumptions on pH optima in enzyme activity assays. We evaluated pH optima of five N-hydrolytic enzymes (casein protease, leucine aminopeptidase, glycine aminopeptidase, alanine aminopeptidase, N-acetyl-β-glucosaminidase) in soils under long-term (145-year) fertilization and crop rotation treatments, as well as a restored prairie, on an Aquic Argiudoll. We additionally tested the pH dependency of three types of non-enzymatic interferences in order to assess the relative importance of controls in determining N-hydrolytic enzyme activity pH optima. For all enzymes, pH–activity relationships varied by soil and exhibited secondary pH optima, though primary pH optima generally agreed with values reported for purified, non-soil enzymes. Enzyme activity pH optima did not reflect soil pH, though soil pH ranged 6.2–7.4 across 145-year treatments. Nonenzymatic interference was generally pH-dependent and soil-specific for protease and N-acetyl-β-glucosaminidase. Though omitting controls for dissolved organic matter tended to have the largest effect on pH optima misestimation, controlling for all three sources of interference had appreciable effects on estimated pH optima values. This study provides a benchmark of empirically determined pH optima of multiple hydrolytic enzymes that catalyze soil N depolymerization. We demonstrate that soil N-hydrolytic enzyme activities exhibit pH optima that generally vary most by enzyme type, and specifically between proteolytic versus chitinolytic enzymes. Because pH optima of these soil enzyme activities can vary among soils differing in management and land use, pH optima should be determined a priori.

Agricultural practices alter the organic carbon dynamics in soil. An experiment was conducted to study the effect of carbon amendments, tillage, and cover cropping on permanganate oxidizable carbon (POXC), total organic carbon (TOC), and wet aggregate stability (WAS) in a 2-year crop sequence (corn–cover crop–cotton–cover crop) at the Texas A&M Research Farm. Two carbon amendments (biochar and composted biosolid) were applied at the rate of 500 kg C ha⁻¹, along with a control. Two tillage practices were evaluated: conventional tillage (CT) and no-tillage (No-Till). A cover crop (CC) mixture of oat, mustard, and pea and no cover crop (No-CC) were also evaluated. Treatments were arranged in a split-split plot design with four replications. Amending the soil with carbon as composted biosolid or biochar affected POXC at both the 0- to 5- and 5- to 15-cm depths. The POXC was significantly higher for the biochar treated plots for corn and CC after corn but significantly lower POXC was observed after cotton with biochar-treated plots. The POXC increased under No-Till compared with CT and CC plots relative to No-CC plots. The TOC was not sensitive to soil management practices. The POXC and TOC both decreased with depth. The WAS greater under No-Till and CC plots. The POXC and WAS were influenced by soil management practices and can be useful indicators to assess short-term soil health improvements. The POXC and WAS were positively related, suggesting that one may be used to predict the other.

An expanded description of particle morphology and the analysis of its relationships with physical properties may help to optimize the selection of raw materials and particle size fractions used as growing media constituents. Previous works have described the outlines of these relations based mostly on sieving procedures to characterize particle size distribution. They have shown limited and sometimes contradictory results due to the different methods used, size fractions selected, and physical properties measured. Also, sieve analysis, which separates particles based on their width, is less accurate for non-spherical particles, which is the case for most growing media constituents. Recent works have promoted the use of dynamic image analysis (DIA) to precisely analyze both particle length and width. Five raw materials were chosen (white and black peats, coir, pine bark, and wood fiber) and sieved to obtain various particle size fractions. For each particle size fraction and the raw materials, the mean weight diameter (MWD), derived from sieving, was calculated, whereas mean particle length and width were determined using a DIA tool, the QicPic device. Also, physical properties were assessed from water retention curves established using Hyprop systems. The statement that the larger the particle size, the higher the air-filled porosity (AFP), the lower the water holding capacity (WHC) was more precisely redefined. Large variations in WHC and AFP mainly occurred for finest particle size fractions, whereas changes were conversely very small or non-existent for larger particle sizes. From data obtained for each particle size fractions, regression models were established to relate mean particle length and width (both determined using DIA) and MWD (determined from sieving) with WHC and AFP. Mean particle length was identified as the most relevant parameter for predicting WHC and AFP of the raw materials tested.

Soil bulk density (BD) is important for measuring changes in soil chemical, physical, and biological properties; however, the measurement is tedious to collect and requires specialized equipment. Database measurements for soil surface BD do not always correspond to present field conditions as field management can alter BD in time. Saturation percentage (SP) is a routine lab measurement. The objectives of this study are to (1) understand if a relationship between BD and SP can be developed and (2) build a model that predicts BD based on a routine low-cost lab analysis. We collected 83 soil samples from different experimental sites around California's Central Valley. At each site, BD, SP, soil organic matter (OM), and soil total organic carbon were measured. A set of models were generated and compared based on their Akaike information criterion (AIC) and adjusted R². The best two models are presented in this paper, and their accuracy and precision in estimating BD were further compared by calculating the root mean square error (RMSE) and the R² of the predicted versus values measured in the field. We determined that a strong relationship between BD and SP exists (R² = 0.70) and that a cubic model that includes SP and OM resulted in the best model to predict BD in California soils. Inclusion of additional data may further strengthen this model or make it applicable for other grower regions.