Nitrogen dynamics as a function of soil types, compaction, and moisture.

In this study, the complex interactions between soil types, compaction, and moisture on nitrogen (N) transformation processes such as ammonia (NH3) volatilization, ammonification, nitrification, and denitrification were examined over a 30-day period using a simulated column approach. Two soil types: loam, and sandy loam, were subjected to three compaction treatments-control, surface, and sub-surface compaction-and two moisture regimes, dry and wet. Liquid urea ammonium nitrate (32-0-0) was used as the N fertilizer source at a rate of 200 kg N ha-1. Key indicators of N transformations were measured, including residual concentrations of ammonium (NH4-N) and nitrate (NO3-N), NO3-N leaching, NH3 volatilization, and nitrous oxide (N2O) emissions. Findings revealed that compaction significantly increased residual NH4-N concentrations in deeper soil profiles, with the highest 190.80 mg kg-1 recorded in loam soil under sub-surface compaction and dry conditions. Nitrification rates decreased across both soil types due to compaction, evidenced by elevated residual NH4-N levels. Increased NO3-N leaching was observed in loam soil (178.06 mg L-1), greater than sandy loam (81.11 mg L-1), due to initial higher residual NO3- in loam soil. The interaction of compaction and moisture most affected N2O emissions, with the highest emissions in control treatments during dry weather at 2.88 kg ha -1. Additionally, higher NH3 volatilization was noted in moist sandy loam soil under control conditions at 19.64 kg ha -1. These results highlight the necessity of considering soil texture, moisture, and compaction in implementing sustainable N management strategies in agriculture and suggest recommendations such as avoiding broadcast application in moist sandy loam and loam soil to mitigate NH3 volatilization and enhance N use efficiency, as well as advocating for readjustment of fertilizer rate based on organic matter content to reduce potential NO3-N leaching and N2O emissions, particularly in loam soil.

Ferrihydrite enrichment in the rhizosphere of unsaturated soil improves nutrient retention while limiting arsenic and uranium plant uptake.

Improvement of nutrient use efficiency and limiting trace elements such as arsenic and uranium bioavailability is critical for sustainable agriculture and food safety. Arsenic and uranium possess different properties and mobility in soils, which complicates the effort to reduce their uptake by plants. Here, we postulate that unsaturated soil amended with ferrihydrite nanominerals leads to improved nutrient retention and helps reduce uptake of these geogenic contaminants. Unsaturated soil is primarily oxic and can provide a stable environment for ferrihydrite nanominerals. To demonstrate the utility of ferrihydrite soil amendment, maize was grown in an unsaturated agricultural soil that is known to contain geogenic arsenic and uranium. The soil was maintained at a gravimetric moisture content of 15.1 ± 2.5%, typical of periodically irrigated soils of the US Corn Belt. Synthetic 2-line ferrihydrite was used in low doses as a soil amendment at three levels (0.00% w/w (control), 0.05% w/w and 0.10% w/w). Further, the irrigation water was fortified (~50 µg L-1 each) with elevated arsenic and uranium levels. Plant dry biomass at maturity was ~13.5% higher than that grown in soil not receiving ferrihydrite, indicating positive impact of ferrihydrite on plant growth. Arsenic and uranium concentrations in maize crops (root, shoot and grain combined) were ~ 20% lower in amended soils than that in control soils. Our findings suggest that the addition of low doses of iron nanomineral soil amendment can positively influence rhizosphere geochemical processes, enhancing nutrient plant availability and reduce trace contaminants plant uptake in sprinkler irrigated agroecosystem, which is 55% of total irrigated area in the United States.

A longitudinal study on morpho-genetic diversity of pathogenic Rhizoctonia solani from sugar beet and dry beans of western Nebraska.

BACKGROUND: Root and stem rot caused by Rhizoctonia solani is a serious fungal disease of sugar beet and dry bean production in Nebraska. Rhizoctonia root rot and crown rot in sugar beet and dry bean have reduced the yield significantly and has also created problems in storage. The objective of this study was to analyze morpho-genetic diversity of 38 Rhizoctonia solani isolates from sugar beet and dry bean fields in western Nebraska collected over 10 years. Morphological features and ISSR-based DNA markers were used to study the morphogenetic diversity. RESULTS: Fungal colonies were morphologically diverse in shapes, aerial hyphae formation, colony, and sclerotia color. Marker analysis using 19 polymorphic ISSR markers showed polymorphic bands ranged from 15 to 28 with molecular weight of 100 bp to 3 kb. Polymorphic loci ranged from 43.26-92.88%. Nei genetic distance within the population ranged from 0.03-0.09 and Shannon diversity index varied from 0.24-0.28. AMOVA analysis based on ΦPT values showed 87% variation within and 13% among the population with statistical significance (p < 0.05). Majority of the isolates from sugar beet showed nearby association within the population. A significant number of isolates showed similarity with isolates of both the crops suggesting their broad pathogenicity. Isolates were grouped into three different clusters in UPGMA based cluster analysis using marker information. Interestingly, there was no geographical correlation among the isolates. Principal component analysis showed randomized distribution of isolates from the same geographical origin. Identities of the isolates were confirmed by both ITS-rDNA sequences and pathogenicity tests. CONCLUSION: Identification and categorization of the pathogen will be helpful in designing integrated disease management guidelines for sugar beet and dry beans of mid western America.

Optimum rates of surface-applied coal char decreased soil ammonia volatilization loss.

Fertilizer N losses from agricultural systems have economic and environmental implications. Soil amendment with high C materials, such as coal char, may mitigate N losses. Char, a coal combustion residue, obtained from a sugar factory in Scottsbluff, NE, contained 29% C by weight. A 30-d laboratory study was conducted to evaluate the effects of char addition on N losses via nitrous oxide (N2 O) emission, ammonia (NH3 ) volatilization, and nitrate (NO3 -N) leaching from fertilized loam and sandy loam soils. Char was applied at five different rates (0, 6.7, 10.1, 13.4, and 26.8 Mg C ha-1 ; char measured in C equivalent) to soils fertilized with urea ammonium nitrate (UAN) at 200 kg N ha-1 . In addition, there were two negative-UAN control treatments: no char (no UAN) and char at 26.8 Mg C ha-1 (no UAN). Treatment applied at 6.7 and 10.1 Mg C ha-1 in fertilized sandy loam reduced NH3 volatilization by 26-37% and at 6.7, 10.1, and 13.4 Mg C ha-1 in fertilized loam soils by 24% compared with no char application. Nitrous oxide emissions and NO3 -N leaching losses were greater in fertilized compared with unfertilized soil, but there was no effect of char amendment on these losses. Because NO3 -N leaching loss was greater in sandy loam than in loam, soil residual N was twofold higher in loam than in sandy loam. This study suggests that adding coal char at optimal rates may reduce agricultural reactive N to the atmosphere by decreasing NH3 volatilization from fertilized soils.

Can char carbon enhance soil properties and crop yields in low-carbon soils?

Restoring soil carbon (C) lost due to intensive farming is a long-term endeavor under current conservation management practices. Application of coal combustion residue (293 g C kg-1 ) from a sugar beet (Beta vulgaris L.) processing factory, hereafter referred to as char, could rapidly restore soil C and productivity in degraded croplands, but data on this potential strategy are unavailable. We assessed the impacts of char application to two relatively low-C soils (10.1 and 12.2 g C kg-1 ) and one relatively high-C soil (17.3 g C kg-1 ) on soil C, soil physical and fertility properties, and crop yields in no-till systems in the Great Plains after 2 yr. Char was disked to 15 cm soil depth at char-C application rates ranging from 0 to 19.7 Mg C ha-1 , corresponding to char application rates ranging from 0 to 67.3 Mg ha-1 . The highest char rate increased C concentration in all soils but increased C stock only in low-C soils. Char did not affect soil penetration resistance, available water, aggregate stability, most nutrients, and crop yields. Char application at high rates increased sulfate, Ca, Mg, and Na concentrations but did not influence other properties. Carbon recovery of the char applied at the highest rate varied among soils from 50 to 85%, but the mechanisms for such differences need further investigation. Short-term duration, low char C concentration, and low application rates may explain the limited char effects. Overall, char application at 19.7 Mg char-C ha-1 (i.e., 67.3 Mg char ha-1 ) increased soil C concentration but had negligible effects on other soil properties and crop yields after 2 yr.

Digital soil mapping in the Bara district of Nepal using kriging tool in ArcGIS.

Digital soil mapping has been widely used to develop statistical models of the relationships between environmental variables and soil attributes. This study aimed at determining and mapping the spatial distribution of the variability in soil chemical properties of the agricultural floodplain lands of the Bara district in Nepal. The study was carried out in 23 Village Development Committees with 12,516 ha total area, in the southern part of the Bara district. A total of 109 surface soil samples (0 to 15 cm depth) were collected and analyzed for pH, organic matter (OM), nitrogen (N), phosphorus (P, expressed as P2O5), potassium (K, expressed as K2O), zinc (Zn), and boron (B) status. Descriptive statistics showed that most of the measured soil chemical variables (other than pH and P2O5) were skewed and non-normally distributed and logarithmic transformation was then applied. A geostatistical tool, kriging, was used in ArcGIS to interpolate measured values for those variables and several digital map layers were developed based on each soil chemical property. Geostatistical interpolation identified a moderate spatial variability for pH, OM, N, P2O5, and a weak spatial variability for K2O, Zn, and B, depending upon the use of amendments, fertilizing methods, and tillage, along with the inherent characteristics of each variable. Exponential (pH, OM, N, and Zn), Spherical (K2O and B), and Gaussian (P2O5) models were fitted to the semivariograms of the soil variables. These maps allow farmers to assess existing farm soils, thus allowing them to make easier and more efficient management decisions and maintain the sustainability of productivity.

Anhydrous Ammonia Injection Depth Does Not Affect Nitrous Oxide Emissions in a Silt Loam over Two Growing Seasons.

Anhydrous ammonia (AA) is a major fertilizer source in North America that can promote greater emissions of nitrous oxide (NO) than other nitrogen (N) fertilizers. Previous studies found that injection of AA at a shallow depth (0.1 m) decreased NO in a rainfed clay loam but increased NO in an irrigated loamy sand compared with the standard injection depth of 0.2 m. The objective of this study was to evaluate the effects of AA injection depth in a silt loam soil used for corn ( L.) production and managed under two contrasting tillage regimes over two consecutive growing seasons (2010 and 2011) in Minnesota. In contrast with previous studies, AA placement depth did not affect NO emissions in either tillage system or in either growing season. Tillage by itself affected NO emissions only in the drier of two seasons, during which NO emissions under no tillage (NT) exceeded those under conventional tillage (CT) by 55%. Soil moisture content under NT was also greater than under CT only in the drier of the two seasons. Effects of AA placement depth and long-term tillage regime on NO emissions exhibit intersite as well as interannual variation, which should be considered when developing NO mitigation strategies. Further study is needed to identify specific soil, climate, or other factors that mediate the contrasting responses to management practices across sites.