J. D. Jabro

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.

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.

Technical Note: Bulk Density, Water Content, and Hydraulic Properties of a Sandy Loam Soil Following Conventional or Strip Tillage

Tillage produces a more favorable soil physical environment for seed germination and plant growth. A 2‐year study was carried out to compare effects of conventional (CT) and strip (ST) tillage practices on soil bulk density ( b), water content ( w), final infiltration rate (Ir) and saturated hydraulic conductivity (Ks) for a Lihen sandy loam where sugarbeet (Beta vulgaris L.) was grown during the 2007 and 2008 growing seasons. Under each tillage system, we measured b and w using soil cores collected from the center of crop rows in all plots at soil surface (0 to 10 cm) and 10‐to 30‐cm depths. At both depths under each tillage system, we measured in‐situ Ir using a pressure ring infiltrometer (PI) and in‐situ Ks using a constant head well permeameter (CHWP). Although we noted a significant difference in b between CT and ST plots at 10‐ to 30‐cm depth in 2007, soil w did not differ significantly between CT and ST plots in 2007. In 2008, soil b and w did not differ significantly between CT and ST plots at both depths. The log‐transformed Ir was affected by tillage practice at P 0.1 in 2007 but was not significantly affected in 2008. The effects of tillage on log‐transformed Ks were significant at P 0.05 in 2007 and P 0.1 in 2008. Soil Ks values were 68% and 56% greater for ST than for CT in 2007 and 2008, respectively. We concluded that ST reduced soil compaction in the row, consequently increased total porosity, reduced b, and thereby increased Ir and Ks in the soil. Keyword. Bulk density, Infiltration, Hydraulic conductivity, Strip tillage, Sugarbeet, Soil compaction. illage is one of the most influential agricultural management practices affecting soil physical and hydraulic characteristics (Lal and Shukla, 2004). In this study, we introduced two types of tillage, the conventional tillage (CT), which consists of several separate operations using different tillage implements following the harvest of one crop in preparation for the next crop, and strip tillage (ST), which involves a single operation with specialized equipment (Evans et al., 2010) that provides alternating strips of tilled and untilled soil. Whether tillage is accomplished by CT or ST, the results of its application are unpredictable, and its effects on soil structure, macropore modifications, and other physical properties at the field scale are known to be contradictory (Lal and Van Doren, 1990; Coutadeur et al., 2002). Moreover, there is little information available regarding the effect of ST on soil physical and hydraulic properties. Tillage has been shown to temporarily improve soil porosity by creating temporary macropores that consequently increase water movement in the soil (Ahuja Submitted for review in February 2011 as manuscript number SW 9065; approved for publication by the Soil & Water Division of ASABE in May 2011. The authors are Jay David Jabro, ASABE Member, Research Soil Scientist, William Bart Stevens, Research Agronomist, William M. Iversen, Physical Scientist, and Robert G. Evans, Agricultural Engineer; Northern Plains Agricultural Research Laboratory, USDA‐ARS, Sidney, Montana. Corresponding author: Jay David Jabro, Northern Plains Agricultural Research Laboratory, USDA‐ARS, 1500 N. Central Avenue, Sidney, MT 59270; phone: 406‐433‐9442; e‐mail: jay.jabro@ars.usda.gov. et al., 1989; Ankeny et al., 1990; Bouma, 1991). On the other hand, tillage has been shown to destroy established aggregates and macropores and disrupt soil pore continuity, thus reduce water flow between the plow layer and subsoil (Bouma, 1991). Beneficial effects of tillage on pore size distribution are temporary because pore spaces that are created either collapse or are sealed during the growing season as a result of raindrop impact and wetting and drying cycles (Topaloglu, 1999). Such inconsistency of results demonstrates the need for additional studies regarding the effect of various tillage practices on soil physical properties. Infiltration rate and saturated hydraulic conductivity are considered the most important parameters describing water flow and chemical transport phenomena in soils (Reynolds and Elrick, 2002). Hydraulic conductivity is affected by bulk density and effective porosity, two commonly measured physical properties of soil fundamental to soil compaction and related agricultural management issues (Strudley et al., 2008). While tilled soil has been shown to have a lower bulk density, higher effective porosity and superior Ks than non‐tilled soil (Rosenberg and McCoy, 1992), tilled soils can also exhibited a higher bulk density, lower effective porosity, and inferior Ks than non‐tilled soils (Chan and Mead, 1989; Dao, 1996). In view of inconsistency of results and the lack of literature about the effect of ST on soil physical and hydraulic properties, objectives of our research were to compare the effects of both CT and ST on four important parameters‐‐bulk density (ρb), gravimetric water content ( w), final infiltration rate (Ir), and saturated hydraulic conductivity (Ks)‐‐in a T

Spatial Variability of Apparent Electrical Conductivity and Cone Index as Measured with Sensing Technologies: Assessment and Comparison

Assessment and interpretation of spatial variability of soil chemical and physical properties are very important for precision farming. The spatial variability of apparent electrical conductivity

Performance Evaluation and Accuracy of Passive Capillary Samplers (PCAPs) for Estimating Real-Time Drainage Water Fluxes

Successful monitoring of pollutant transport through the soil profile requires accurate, reliable, and appropriate instrumentation to measure amount of drainage water or flux within the vadose layer. We evaluated the performance and accuracy of automated passive capillary wick samplers (PCAPs) for their ability to monitor and estimate real-time drainage water fluxes by comparing amounts of drainage recorded by the datalogger from the tipping buckets with manually collected drainage amounts. Drainage water fluxes were online estimated and manually collected below the rootzone of a sugarbeet-potato-barley using five years of data.

Field performance of three real-time moisture sensors in sandy loam and clay loam soils

ABSTRACT The study was conducted to evaluate HydraProbe (HyP), Campbell Time Domain Reflectometry (TDR) and Watermarks (WM) moisture sensors for their ability to estimate water content based on calibrated neutron probe (NP) measurements. The three sensors were in-situ tested under natural weather conditions over a 3-yr period in a sandy loam and clay loam soils planted to grass. The HyP, TDR and WM sensors were evaluated for their ability to estimate soil moisture contents by comparing their outputs with those of NP measurements. Results showed that HyP, TDR and WM provided different estimates of soil moisture contents in both soils. Nevertheless, our work suggests that soil moisture sensors including those used in this study can be made suitable for irrigation scheduling without in-situ calibrations by simply setting the upper and lower irrigation trigger limits for each sensor and each soil type. The upper trigger point occurs directly after irrigation event (near field capacity) and the lower trigger point is based on about 50% depletion of available water in the crop rootzone and is occurs prior to irrigation refill. This approach can significantly help irrigators to achieve their irrigation scheduling and productivity goals without consuming any time onsite or soil specific calibrations.

REPEATABILITY OF SOIL APPARENT ELECTRICAL CONDUCTIVITY MEASURED BY A COULTER SENSOR

Apparent electrical conductivity (ECa) measured using an on-the-go coulter sensor offers advantages for mapping soil variability because detailed data can be collected easily and inexpensively using on-the-go ECa sensors. However, there has been little research investigating the repeatability of these sensors, which may be defined as their ability to reproduce the same ECa measurement when operated in the same location under the same operating and field conditions. If the output of the coulter ECa sensor is not repeatable, the accuracy and reliability of the resulting maps and management decisions would be compromised. Therefore, the objective of this study was to evaluate the repeatability of the coulter sensor by comparing ECa data from two passes in barley stubble at two 1.6-ha sites, one with a sandy loam soil texture (Nesson site) and the other, a clay loam soil texture (Montana State University Eastern Agricultural Research Center site). Sampling points were approximately 1.45 m apart in the direction of travel for both passes. The ECa measurements from both passes were compared at shallow (0-30 cm) and deep (0-90 cm) soil depths. The coefficients of variation of ECa measurements for shallow and deep depths from pass 1 were higher than those from pass 2 at both sites. The root mean square error values of ECa measurements between pass 1 and pass 2 at shallow and deep depths for the Nesson site were 0.76 and 0.51 mS m−1, respectively, whereas the root mean square errors for the Montana State University Eastern Agricultural Research Center site were 4.06 and 2.93 mS m−1 at shallow and deep depths, respectively. The repeatability was evaluated using a 95% confidence interval for the differences between ECa measurements of the two passes. Results demonstrate marginally acceptable repeatability between the two passes at shallow depths and acceptable repeatability at deep depths. The reasons for lack of agreement between pass 1 and pass 2 in ECa measurements at shallow depths could have resulted from soil disturbance and compaction caused by the coulter sensor during the pass 1 process. Regardless of discrepancies for shallow depths, the results indicate that the on-the-go ECa sensors can be useful and provide reliable data for describing field spatial variability in precision farming. This study was conducted to represent field conditions under which this equipment will likely be used, and further work is needed to confirm the repeatability of the coulter at shallow depths.

In-Situ Soil-Water Retention and Field Water Capacity Measurements in Two Contrasting Soil Textures

The primary objective of this study was to estimate the in-situ field water capacity (FWC) from the soil-water retention curve developed from volumetric water content, ? and water matric potential, ? data collected in the field using soil moisture sensors in two soils. The soils are Lihen sandy loam and Savage clay loam. Six 117 cm × 117 cm metal frames, 30 cm in height were inserted 5- to 1 0 cm into soil. Two Time Domain Reflectrometry (TDR) sensors were installed in the center of the frame and two Watermark (WM) sensors were installed in the SW corner at 15 and 30 cm depths to continuously monitor soil ? and ?, respectively. A neutron probe (NP) access tube was installed in the NE corner of each frame to measure soil ? used for TDR calibration. The soil inside each frame was saturated by applying approximately 18 to 20 cm of water intermittently to saturate the upper 50 to 60 cm of soil. Frames were