Long-term tillage, cropping sequence, and nitrogen fertilization effects on soil carbon and nitrogen dynamics

Management practices that may increase soil organic matter (SOM) storage include conservation tillage, especially no till (NT), enhanced cropping intensity, and fertilization. My objectives were to evaluate management effects on labile [soil microbial biomass (SMB) and mineralizable, particulate organic matter (POM), and hydrolyzable SOM] and slow (mineral-associated and resistant organic) C and N pools and turnover in continuous sorghum [Sorghum bicolor (L.) Moench.], wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.], sorghum-wheat/soybean, and wheat/soybean sequences under convent ional tillage (CT) and NT with and without N fertilization. A Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochepts) in southern central Texas was sampled at three depth increments to a 30-cm depth after wheat, sorghum, and soybean harvesting. Soil organic C and total N showed similar responses to tillage, cropping sequence, and N fertilization following wheat, sorghum, and soybean. Most effects were observed in surface soils. NT significantly increased SOC. Nitrogen fertilization significantly increased SOC only under NT. Compared to NT or N addition, enhanced cropping intensity only slightly increased SOC. Estimates of C sequestration rates under NT indicated that SOC would reach a new equilibrium after 20 yr or less of imposition of this treatment. Labile pools were all significantly greater with NT than CT at 0 to 5 cm and decreased with depth. SMB, mineralizable C and N, POM, and hydrolyzable C were highly correlated with each other and SOC, but their slopes were significantly different, being lowest in mineralizable C and highest in hydrolyzable C. These results indicated that different methods determined various fractions of total SOC. Results from soil physical fractionation and 13C concentrations further supported these observations. Carbon turnover rates increased in the sequence: ROC < silt- and clayassociated C < microaggregate-C < POM-C. Long-term incubation showed that 4 to 5% of SOC was in active pools with mean residence time (MRT) of about 50 days, 50% of SOC was in slow pools with an average MRT of 12 years, and the remainder was in resistant pools with an assumed MRT of over 500 years

Soil Texture and Cultivar Effects on Rice (Oryza sativa, L.) Grain Yield, Yield Components and Water Productivity in Three Water Regimes

The objective of this study was to determine the effects of water regime/soil condition (continuous flooding, saturated, and aerobic), cultivar ('Cocodrie' and 'Rondo'), and soil texture (clay and sandy loam) on rice grain yield, yield components and water productivity using a greenhouse trial. Rice grain yield was significantly affected by soil texture and the interaction between water regime and cultivar. Significantly higher yield was obtained in continuous flooding than in aerobic and saturated soil conditions but the latter treatments were comparable to each other. For Rondo, its grain yield has decreased with soil water regimes in the order of continuous flooding, saturated and aerobic treatments. The rice grain yield in clay soil was 46% higher than in sandy loam soil averaged across cultivar and water regime. Compared to aerobic condition, saturated and continuous flooding treatments had greater panicle numbers. In addition, panicle number in clay soil was 25% higher than in sandy loam soil. The spikelet number of Cocodrie was 29% greater than that of Rondo, indicating that rice cultivar had greater effect on spikelet number than soil type and water management. Water productivity was significantly affected by the interaction of water regime and cultivar. Compared to sandy loam soil, clay soil was 25% higher in water productivity. Our results indicated that cultivar selection and soil texture are important factors in deciding what water management option to practice

Soil Carbon and Material Fluxes Across the Eroding Alaska Beaufort Sea Coastline

Carbon, nitrogen, and material fluxes were quantified at 48 sampling locations along the 1957 km coastline of the Beaufort Sea, Alaska. Landform characteristics, soil stratigraphy, cryogenic features, and ice contents were determined for each site. Erosion rates for the sites were quantified using satellite images and aerial photos, and the rates averaged across the coastline increased from 0.6 m yr-1 during circa 1950-1980 to 1.2 m yr-1 during circa 1980-2000. Soils were highly cryoturbated, and organic carbon (OC) stores ranged from 13 to 162 kg OC m-2 in banks above sea level and averaged 63 kg OC m-2 over the entire coastline. Long-term (1950-2000) annual lateral fluxes due to erosion were estimated at -153 Gg OC, -7762 Mg total nitrogen, -2106 Tg solids, and -2762 Tg water. Total land area loss along the Alaska Beaufort Sea coastline was estimated at 203 ha yr-1. We found coastal erosion rates, bank heights, soil properties, and material stores and fluxes to be extremely variable among sampling sites. In comparing two classification systems used to classifying coastline types from an oceanographic, coastal morphology perspective and geomorphic units from a terrestrial, soils perspective, we found both systems were effective at differentiating significant differences among classes for most material stores, but the coastline classification did not find significant differences in erosion rates because it lacked differentiation of soil texture

Impact of Excess Magnesium Salt Supply on Rice Yield, Physiological Response, and Grain Mineral Content

Magnesium nutrition in plants has remained largely unexplored compared to other essential elements. Although the impact of magnesium deficiency on plants has been reported from numerous studies, the responses of plants to excess magnesium salt levels have received less attention. Using five different magnesium levels (0, 500, 1000, 1500, and 2000 ppm) and two magnesium sources (MgSO4 and MgCl2), this study evaluated the effect of excess magnesium salts on rice production and associated physiological processes on a hybrid rice cultivar ‘XP 753’. Rice morphological and physiological parameters, including plant growth, biomass, root morphological features, tissue and grain mineral concentrations, membrane injury (MI), chlorophyll, malondialdehyde (MDA) concentrations, proline concentrations, as well as gas exchange parameters, were evaluated. A dose-dependent reduction in above- and below-ground shoot and root morphological features was observed under the application of magnesium salts on the soil substrate. Analysis of physiological parameters demonstrated that an inhibition in plant growth, biomass, and yield was due to the decrease in total chlorophyll content, net photosynthesis rate, and membrane stability in rice. Furthermore, this study showed that the application of magnesium salts to soil interfered with the uptake and translocation of minerals and significantly increased reactive oxygen species (ROS), malondialdehyde (MDA), and proline levels, indicating the toxic effects of excess magnesium salts on rice plants

Optimizing Conditions for the Measurement of Soil Inorganic Nitrogen with a Micro-Plate Reader

There are numerous methods for measuring inorganic nitrogen (N) in soils, but many of these are complex or require expensive equipment. In order to seek an accurate and rapid measurement method, we optimized the conditions for soil inorganic nitrogen (N) (NH4+-N and NO3–N) determination with a micro-plate reader; a systematic study was carried out. The effects of extraction regent concentrations, ratios of extraction solution to the soil, extraction time, extracted solution storage methods and time, and reaction time on soil inorganic N measurement were investigated. Results showed that all tested conditions except the storage method had a significant effect on the determination of soil NH4+-N and NO3–N. Compared with the non-stored treatment, the value of the measured soil nitrate-nitrogen increased after being stored in a refrigerator for seven weeks, while that for ammonium-nitrogen content was reduced. The appropriate protocol was using extracting solution directly to determine the content of NH4+-N and NO3–N in soil (otherwise, keep it at room temperature), 1.0 mol/L KCl as the extraction regent, solution/soil ratio with 10:1, extraction for 45 min, and reaction for 25 min (only for NH4+-N). The recovery rate of adding standard solution was above 99% as it met the detection requirements

Effect of Cover Crop Type and Application Rate on Soil Nitrogen Mineralization and Availability in Organic Rice Production

In drill-seeded, delay-flooded organic rice production, reliable predictions of N supply from cover crop (CC) residues to subsequent rice are still a challenge. An incubation was conducted to determine the effects of CC types (clover, ryegrass, clover and ryegrass mixtures, and fallow), residue application rates (0, 0.6, 1.2, 1.8, and 2.4%) and incubation time on soil CO2 evolution and N mineralization and availability. The cumulative CO2 evolution linearly increased with increasing residue rate. Compared to the control, adding CCs residue significantly increased the cumulative CO2 emission, which was greatest in soils with clover or mixtures of clover and ryegrass, followed by fallow, and lowest in soils with ryegrass. The modeling results indicated clover had the greatest initial C and N mineralization rates and the shortest half-lives. A temporary decrease in soil mineral N caused by immobilization occurred at the initial incubation stage in all treatments. However, the trend reversed progressively, with the clover treatment requiring the shortest time to meet the crossover point. The results suggested clover was the optimal CC type, 0.6% was the optimal residue rate, and a minimum of 27 days between CC termination and rice planting was required to maximize mineral N supply for organic rice

Effect of Cover Crop Type and Application Rate on Soil Nitrogen Mineralization and Availability in Organic Rice Production

In drill-seeded, delay-flooded organic rice production, reliable predictions of N supply from cover crop (CC) residues to subsequent rice are still a challenge. An incubation was conducted to determine the effects of CC types (clover, ryegrass, clover and ryegrass mixtures, and fallow), residue application rates (0, 0.6, 1.2, 1.8, and 2.4%) and incubation time on soil CO2 evolution and N mineralization and availability. The cumulative CO2 evolution linearly increased with increasing residue rate. Compared to the control, adding CCs residue significantly increased the cumulative CO2 emission, which was greatest in soils with clover or mixtures of clover and ryegrass, followed by fallow, and lowest in soils with ryegrass. The modeling results indicated clover had the greatest initial C and N mineralization rates and the shortest half-lives. A temporary decrease in soil mineral N caused by immobilization occurred at the initial incubation stage in all treatments. However, the trend reversed progressively, with the clover treatment requiring the shortest time to meet the crossover point. The results suggested clover was the optimal CC type, 0.6% was the optimal residue rate, and a minimum of 27 days between CC termination and rice planting was required to maximize mineral N supply for organic rice

Soil Carbon Sequestration in Sorghum Cropping Systems: Evidence From Stable Isotopes and Aggregate-Size Fractionation

Abstract: Management practices can influence both the quantity of soil organic carbon (SOC) and its distribution into different fractions or pools. We investigated SOC sequestration potentials of cropping systems in nearsurface (0-5 cm) samples through soil size and density fractionation coupled with acid hydrolysis and natural abundance of stable isotopes (δ C values for soils from SWSoy varied from −20‰ to −22‰, reflecting a mixed input from C 3 -derived and C 4 -derived residue input. For whole soil and all aggregate-size fractions, SOC concentrations were significantly higher for NT than conventional tillage. However, the effects of cropping system and N fertilization on SOC interacted with tillage. Greater SOC for enhanced cropping (SWSoy) or N fertilization was observed only under NT. The fraction of &lt;53 μm represented a greater proportion of soil than other aggregate-size fractions. Our long-term study indicated that SOC and its various fractions, including more resistant, can be increased by NT with enhanced cropping and N fertilization

Spatial Variation of Tundra Soil Organic Carbon Along the Coastline of Northern Alaska

Coastal erosion plays an important role in the terrestrial-marine-atmosphere carbon cycle. This study was conducted to explore the spatial variation of soil organic carbon (SOC) and other soil properties along the coastline of northern Alaska. A total of 769 soil samples, from 48 sites along over 1800-km of coastline in northern Alaska, were collected during the summers of 2005 and 2006. A geological information system (GIS) and a geostatistical method (ordinary kriging) were coupled to investigate the spatial variation of SOC along the coastline. SOC have a big variation ranging from 0.8 to 187.4 kg C m(-2) with the greatest value observed in the middle and lowest in the northeastern coastline. Compared to the I-D model or the I-D model with shortcut distance, the 2-D model was more reasonable to describe SOC along the coastline. The Gaussian correlation structure model had less prediction error than other examined geostatistical models. All mapping results also indicate that soils of the northwestern coastline stored greater SOC than those of the northeastern coastline. The estimation of total SOC along the coastline of northern Alaska was 6.86 10(7) kg m(-1). The prediction errors indicated that greater errors were observed in both ends of the coastline than were observed in other fractions, although the range was from 0.739 to 0.779. Our study suggests that the isotropic 2-D model without a trend, with the nugget effect and the Gaussian correlation structure is a useful tool to investigate SOC in large scale. Results of stable isotope of organic matter indicate that SOC are mainly derived from C3 plant, which ranged from - 30 parts per thousand. to - 22 parts per thousand.. (C) 2009 Elsevier B.V. All rights reserved

The effect of soil texture on rice production.

<p>The effect of soil texture on rice production.</p