William B. Stevens

Soil carbon dioxide emission and carbon content as affected by irrigation, tillage, cropping system, and nitrogen fertilization.

Management practices can influence soil CO(2) emission and C content in cropland, which can effect global warming. We examined the effects of combinations of irrigation, tillage, cropping systems, and N fertilization on soil CO(2) flux, temperature, water, and C content at the 0- to 20-cm depth from May to November 2005 at two sites in the northern Great Plains. Treatments were two irrigation systems (irrigated vs. non-irrigated) and six management practices that contained tilled and no-tilled malt barley (Hordeum vulgaris L.) with 0 to 134 kg N ha(-1), no-tilled pea (Pisum sativum L.), and a conservation reserve program (CRP) planting applied in Lihen sandy loam (sandy, mixed, frigid, Entic Haplustolls) in western North Dakota. In eastern Montana, treatments were no-tilled malt barley with 78 kg N ha(-1), no-tilled rye (Secale cereale L.), no-tilled Austrian winter pea, no-tilled fallow, and tilled fallow applied in dryland Williams loam (fine-loamy, mixed Typic Argiborolls). Irrigation increased CO(2) flux by 13% compared with non-irrigation by increasing soil water content in North Dakota. Tillage increased CO(2) flux by 62 to 118% compared with no-tillage at both places. The flux was 1.5- to 2.5-fold greater with tilled than with non-tilled treatments following heavy rain or irrigation in North Dakota and 1.5- to 2.0-fold greater with crops than with fallow following substantial rain in Montana. Nitrogen fertilization increased CO(2) flux by 14% compared with no N fertilization in North Dakota and cropping increased the flux by 79% compared with fallow in no-till and 0 kg N ha(-1) in Montana. The CO(2) flux in undisturbed CRP was similar to that in no-tilled crops. Although soil C content was not altered, management practices influenced CO(2) flux within a short period due to changes in soil temperature, water, and nutrient contents. Regardless of irrigation, CO(2) flux can be reduced from croplands to a level similar to that in CRP planting using no-tilled crops with or without N fertilization compared with other management practices.

Soil greenhouse gas emissions affected by irrigation, tillage, crop rotation, and nitrogen fertilization.

Management practices, such as irrigation, tillage, cropping system, and N fertilization, may influence soil greenhouse gas (GHG) emissions. We quantified the effects of irrigation, tillage, crop rotation, and N fertilization on soil CO, NO, and CH emissions from March to November, 2008 to 2011 in a Lihen sandy loam in western North Dakota. Treatments were two irrigation practices (irrigated and nonirrigated) and five cropping systems (conventional-tilled malt barley [ L.] with N fertilizer [CT-N], conventional-tilled malt barley with no N fertilizer [CT-C], no-tilled malt barley-pea [ L.] with N fertilizer [NT-PN], no-tilled malt barley with N fertilizer [NT-N], and no-tilled malt barley with no N fertilizer [NT-C]). The GHG fluxes varied with date of sampling and peaked immediately after precipitation, irrigation, and/or N fertilization events during increased soil temperature. Both CO and NO fluxes were greater in CT-N under the irrigated condition, but CH uptake was greater in NT-PN under the nonirrigated condition than in other treatments. Although tillage and N fertilization increased CO and NO fluxes by 8 to 30%, N fertilization and monocropping reduced CH uptake by 39 to 40%. The NT-PN, regardless of irrigation, might mitigate GHG emissions by reducing CO and NO emissions and increasing CH uptake relative to other treatments. To account for global warming potential for such a practice, information on productions associated with CO emissions along with NO and CH fluxes is needed.

Development of Strip Tillage on Sprinkler Irrigated Sugarbeet

A project to evaluate new technologies for strip tillage of small seeded crops was initiated in fall 2003 near Sidney, Montana, for sprinkler irrigated sugarbeet (Beta vulgaris L.) to be grown in 2004. Strip till treatments were compared to conventional grower tillage practices in fifty-six 15- × 25-m (48- × 80-ft) side-by-side plots. Both treatments were flat planted with no ridges or beds. All strip tillage and fertilization was done in the fall after removal of a malt barley crop. Conventional tillage was done in the fall at the Sidney site and in the spring at the Nesson site. Thirty-centimeter (12-in.) wide strips were tilled directly into the straw residues about 20 cm (8 in.) deep using straight and paired fluted coulters and a modified parabolic ripping shank followed by a crows-foot packer wheel. Toothed-wheel row cleaners were installed in front of the straight coulter to move loose residue to the side to avoid plugging. At the same time, dry fertilizer was shanked (banded) about 8 to 13 cm (3 to 5 in.) below the anticipated seed placement location. Sugarbeet were planted about 2.5 cm (1 in.) deep with 60-cm (24-in.) spacing between rows in the spring. Toothed-wheel row cleaners were also placed in front of each row on the planter to move any residue displaced by winter storms. Operation of the strip tillage machine required about 25 tractor horsepower per row, but substantial fuel savings were realized with this system by reducing the number of tractor equipment field passes by up to 75%. In 2004, 2006, 2007, and 2008 there were no significant differences in yields or sugar production between the two tillage treatments; however, in 2005 the strip tilled plots produced about 17% greater yields (tonnage and gross sugar). This benefit in 2005 was primarily due to the standing straw stubble in the strip tilled plots that protected sugarbeet seedlings from blowing soil during a spring wind storm that severely damaged seedlings in the conventionally tilled plots where there was no surface crop residue. It was concluded that strip tillage must be considered as part of a larger cropping system that affects timing and equipment choices for planting, cultivation, spraying, and harvesting as well as tillage and other cultural practices. Based on these results, it is generally recommended that strip tillage should be performed in the fall on clay soils in eastern Montana where it has been shown to result in better seedbed conditions than spring strip tillage. Whereas lighter, sandy soils would probably produce equally well when strip tilled in the spring, which could then be combined with planting into a single pass tillage, fertilizing, and planting operation. Banding fertilizer is highly recommended under strip till to increase fertilizer use efficiencies and reduce input costs. RTK-GPS guided steering in combination with some type of mechanical steering assistance on the implements are also recommended for both strip tilling, planting, and cultivation (if needed).

Tillage Effects on Physical Properties in Two Soils of the Northern Great Plains

Tillage practices profoundly affect soil physical and hydraulic properties. It is essential to select a tillage practice that sustains the soil physical properties required for successful growth of agricultural crops. We evaluated the effects of conventional (CT) and strip (ST) tillage practices on bulk density (rho(b)), gravimetric water content (theta(w)), and saturated hydraulic conductivity (K(s)) at the soil surface and at 10- to 15-cm depth in two soils of the Northern Great Plains (NGP). Soil cores were collected from each plot at 0- to 10- and 10- to 20-cm depths under each tillage practice at both sites to measure rho(b) and theta(w). In-situ K(s) measurements at the soil surface and at 10- to 15-cm depth were determined using a pressure head infiltrometer (PHI) and a constant head well permeameter (CHWP), respectively, at two sites, one in North Dakota (Nesson, mapped as Lihen sandy loam) and one in Montana (EARC, mapped as Savage clay loam). The K(s) measurements were made approximately 1 m apart in the center of crop rows within CT and ST plots of irrigated sugarbeet ( Beta vulgaris L.). Tillage treatments significantly affected soil rho(b) and theta(w) in clay loam soil at the EARC site, while rho(b) and theta(w) did not differ between CT and ST in sandy loam at the Nesson site. The log-transformed K(s) at the soil surface did not differ significantly between CT and ST practices at either site. The effect of tillage on log-transformed K(s) at the 10- to 15-cm depth was significant in both sandy loam and clay loam soils at P < 0.10 and 0.05 levels, respectively. The K(s) values at 10- to 15-cm depth were 23% and 138% greater for ST than for CT at Nesson and EARC sites, respectively. Differences in soil compaction as evaluated through rho(b) data at 10- to 20-cm depth explain K(s) variations between the CT and ST systems at both sites. It was concluded that the CT operations increased soil compaction, which consequently altered rho(b), thereby reducing K(s) in the soil.

Net Global Warming Potential and Greenhouse Gas Intensity Influenced by Irrigation, Tillage, Crop Rotation, and Nitrogen Fertilization

Little information exists about how global warming potential (GWP) is affected by management practices in agroecosystems. We evaluated the effects of irrigation, tillage, crop rotation, and N fertilization on net GWP and greenhouse gas intensity (GHGI or GWP per unit crop yield) calculated by soil respiration (GWP and GHGI) and organic C (SOC) (GWP and GHGI) methods after accounting for CO emissions from all sources (irrigation, farm operations, N fertilization, and greenhouse gas [GHG] fluxes) and sinks (crop residue and SOC) in a Lihen sandy loam from 2008 to 2011 in western North Dakota. Treatments were two irrigation practices (irrigated vs. nonirrigated) and five cropping systems (conventional-till malt barley [ L.] with N fertilizer [CTBN], conventional-till malt barley with no N fertilizer [CTBO], no-till malt barley-pea [ L.] with N fertilizer [NTB-P], no-till malt barley with N fertilizer, and no-till malt barley with no N fertilizer [NTBO]). While CO equivalents were greater with irrigation, tillage, and N fertilization than without, NO and CH fluxes were 2 to 218 kg CO eq. ha greater in nonirrigated NTBN and irrigated CTBN than in other treatments. Previous years crop residue and C sequestration rate were 202 to 9316 kg CO eq. ha greater in irrigated NTB-P than in other treatments. Compared with other treatments, GWP and GWP were 160 to 9052 kg CO eq. ha lower in irrigated and nonirrigated NTB-P. Similarly, GHGI and GHGI were lower in nonirrigated NTB-P than in other treatments. Regardless of irrigation practices, NTB-P may lower net GHG emissions more than other treatments in the northern Great Plains.

CHARACTERIZATION OF SPATIAL VARIABILITY OF SOIL ELECTRICAL CONDUCTIVITY AND CONE INDEX USING COULTER AND PENETROMETER-TYPE SENSORS

Assessment and management of spatial variability of soil chemical and physical properties (e.g., soil texture, organic matter, salinity, compaction, and nutrient content) are very important for precision farming. With current advances in sensing technology, soil electrical conductivity (EC) mapping is considered the most efficient and inexpensive method that can provide useful information about soil variability within agricultural fields. The objectives of this research study were to determine if Coulter and penetrometer-type EC sensors produce similar descriptions of soil variability, and if EC and cone index (CI) measured using a penetrometer-type sensor are correlated. The spatial variability of apparent EC (ECa) and penetration resistance expressed as CI for soil compaction were investigated with Coulter and penetrometer sensing technologies. The study was conducted in April 2005 at the research farm located near Williston, North Dakota, on a Lihen sandy loam (sandy, mixed, frigid Entic Haplustoll). The ECa and CI values generated by the penetrometer sensor were averaged over a 0- to 30-cm depth for comparison with values measured using the Coulter sensor over the same 0- to 30-cm depth. Classical and spatial statistics were used to evaluate spatial dependency and assess the overall soil variability within the experimental site. The statistical results indicated that the ECa data from both Coulter and penetrometer sensors exhibited similar spatial trends across the field that may be used to characterize the variability of soil for a variety of important physical and chemical properties. The coefficients of variation (CVs) of log-transformed ECa data from Coulter and penetrometer sensors were 11.3% and 18.9%, respectively. The mean difference, Md, of log-transformed ECa measurements between these two devices was also significantly different from zero (Md = 0.44 mS/m; t = 31.5, n = 134; P < 0.01). Soil ECa and CI parameters were spatially distributed and presented strong to medium spatial dependency within the mapped field area. Results from this study indicate the effectiveness of the ECa and CI sensors for identifying spatial variability of soil properties, and thus, the sensors may be useful tools for managing spatial variability in agricultural fields.

Passive Capillary Sampler for Measuring Soil Water Drainage and Flux in the Vadose Zone: Design, Performance, and Enhancement

Various soil water samplers are used to monitor, measure, and estimate drainage water, fluxes, and solute transport in the vadose zone. Passive capillary samplers (PCAPs) have shown potential to provide better measurements and estimates of soil water drainage and fluxes than other lysimeters designs and field sampling methods. Twelve automated PCAPs with sampling surface dimensions of 31 cm width × 91 cm long and 87 cm in height were designed, constructed, and tops of the samplers were placed 90 cm below the soil surface in a Lihen sandy loam (sandy, mixed, frigid Entic Haplustoll). The PCAPs were installed to continually quantify the amount of drainage water and fluxes occurring under sugarbeet (Beta vulgaris L.) and malting barley (Hordeum vulgare L.) crops treated with 30 mm (low replacement) and 15 mm (high replacement) irrigation frequencies. Drainage water was extracted, collected, and measured periodically (weekly from May to mid-August, biweekly until late September, and monthly thereafter until mid-November). This design incorporated Bluetooth wireless technology to enable an automated datalogger to transmit drainage water and flux data simultaneously every 15 min to a remote host. Real-time seamless monitoring and measuring of drainage water and fluxes was thus possible without the need for costly time-consuming supportive operations. The mean difference (Md) values between manually extracted and logged drainage water for high frequency (Md = 0.80 mm) and low frequency (Md = 0.26 mm) irrigations were small and not significantly different from zero. The Root Mean Square Error (RMSE) of 2.46 and 7.83 mm for high frequency and low frequency irrigations, respectively, were also small. Despite small variations in drainage water results, our novel PCAP design provided an accurate and convenient way to measure water drainage and flux in the vadose zone. Moreover, it offered a significantly larger coverage area (2700 cm2) than similarly designed vadose zone fluxmeters or PCAPs. In the course of one years field testing, we incorporated several additional enhancements such as PCAP container, tipping bucket and datalogger unit, all of which we recommend for optimal performance.

Development of combined site-specific MESA and LEPA methods on a linear move sprinkler irrigation system.

A site-specific controller, hardware and software systems were developed with the capability to switch between either mid-elevation spray application (MESA) or low-energy precision application (LEPA) methods. These systems were field tested and used to manage site-specific irrigations under a linear move sprinkler system and simultaneously varied water application depths by plot as the machine traveled back and forth across the field. The controller and modifications to the water application methods utilized off-the-shelf components as much as possible. The linear move system was modified so that every plot could be irrigated using either MESA or LEPA methods. A programmable logic controller (PLC)-based control system was utilized to activate grouped networks of electric over air-activated control valves. Both the depth and method of irrigation were varied depending on the location of each plot in the field as provided by a low-cost WAAS enabled GPS system mounted on the machine. When not being used, low-cost pneumatic cylinders lifted the LEPA heads above the MESA heads to avoid spray interference when the MESA mode was operating over a specified plot width and length. The control system was used on fifty-six 15- × 24.4-m (50- × 80-ft) plots as well as several other adjacent research projects in which there were a mix of crops and a prescribed set of management experiments. While this particular application was designed specifically for a large, complex agronomic research project to address artificially imposed spatial variability water management, the same controllers, valves and general software could be easily adapted to field scale commercial irrigation.

Spatial Variability and Correlation of Selected Soil Properties in the Ap Horizon of a CRP Grassland

Knowledge of the spatial variability of soil properties in agricultural fields is important for implementing various precision agricultural management practices. This article examines spatial variation of selected soil physical and chemical properties and explores their spatial correlation in the Ap horizon of a Lihen sandy loam soil (sandy, mixed, frigid Entic Haplustoll) within a field of grass-alfalfa Conservation Reserve Program (CRP) land. Soil measurements were made on a 16 x 36-m grid sampling pattern. Soil properties including penetration resistance (PR), bulk density (rho b), and gravimetric water content (theta m) were measured by collecting undisturbed soil cores from 5- to 10-cm and 20- to 25-cm depths. Additional disturbed soil samples were collected for particle size distribution, electrical conductivity (EC(e)), and pH analysis. The two depths were averaged for the assessment of spatial distribution, relationships and interpolation of soil properties. Soil saturated hydraulic conductivity (K(s)) and total porosity (epsilon(T)) for the 0- to 25-cm depth were estimated from rho b , theta m , and volumetric water content at field capacity (FC) level. Soil properties were analyzed using both classical and geostatistical methods that included descriptive statistics, semivariograms, cross-semivariograms, spatial kriged and co-kriged prediction maps and interpolation. Results indicated that small to moderate spatial variability existed across the field for soil properties studied . Furthermore, cross-semivariograms exhibited a strong negative spatial interdependence between soil PR and theta m, epsilon(T), and lnK(s). Spatial variability of soil theta(m), rho b, PR, ECe, pH, and clay content and their spatial correlation in the Ap horizon of the CRP grassland were attributed to a combination of previous farming practices, topographic characteristics, vegetation history, soil erosion, and weather conditions at this site.

Use of nitrous oxide as a purge gas for automated nitrogen isotope analysis by the Rittenberg technique

An apparatus that operates with an isotope-ratio mass spectrometer to automatically perform nitrogen isotope analyses by the Rittenberg technique was modified to permit the use of nitrous oxide (N2O) instead of Freon (CCl2F2 or CHClF2) for the purging of air prior to hypobromite oxidation of ammonium-N to N2 in a plastic microplate. Analytical performance was unaffected by the modifications. Up to 768 samples can be processed in a single loading, at a rate of 6 to 12 samples/h. Within the range of 0.2 to 20 atom % 15N, isotope-ratio analyses of 50 to 200 μg of N using the automated Rittenberg apparatus (ARA) with a double-collector mass spectrometer were accurate to within 0.7%, as compared to manual Rittenberg analyses of 1 mg of N using the same mass spectrometer with a dual-inlet system. Automated analyses of 20μg of N were accurate to within 2%, and automated analyses of 10 μg of N were accurate to within 7%. The relative standard deviation for measurements at the natural abundance level (10 analyses, 20-200 μg of N) was < 0.04 %.