Jay D. Jabro

FIELD EVALUATION AND PERFORMANCE COMPARISON OF SOIL MOISTURE SENSORS

Agricultural producers who choose to supplement their crops’ water requirement are able to determine irrigation scheduling practices better when the soil water content of their fields is known. The objective of this study was to statistically evaluate numerous sensors for their ability to accurately estimate water content in a 90-cm soil profile, based on calibrated neutron probe measurements. The sensors tested were Irrometers, Watermarks, EnviroScan, Troxler Sentry, AquaTel, AquaFlex, Trime, AquaPro, and GroPoint. The sensors were field tested at different water content levels and a variety of irrigation frequencies over a 3-year period in a Warden silt loam soil (Coarse-silty, mixed, mesic, Xerollic Camborthids) planted to alfalfa. The default factor calibration was used to estimate the soil water content from all sensors except the neutron probe, which was calibrated for the soil using the gravimetric moisture content method. The Irrometer and Watermark sensors utilized a local soil water retention relationship in order to convert soil water potential into volumetric water content. The results suggest that most sensors were able to follow the general trends successfully as soil water content changed during the growing season, and there was significant correlation between the sensors and the neutron probe readings. Although sensor trends were similar, visual and statistical analyses indicated that the actual measured values varied significantly between the sensors and the calibrated neutron probe measurements. Therefore, a soil specific calibration of each sensor would have been necessary to obtain a high degree of absolute accuracy in soil water content measurements. The results suggest that irrigators can still use uncalibrated sensors to improve their watering schedules by setting irrigation trigger points that may relate only to a specific sensor in a specific soil. These trigger points cannot easily be related to different soils, different sensors, and other sources of information such as extension fact sheets and research publications, however, because the actual water content measurements may not be correct.

Tillage Depth Effects on Soil Physical Properties, Sugarbeet Yield, and Sugarbeet Quality

Tillage depth influences the soil–water–plant ecosystem, thereby affecting crop yield and quality. The effects of tillage depth on soil physical properties and sugarbeet (Beta vulgaris L.) yield and quality were evaluated. A field study composed of two tillage depths [10 cm, referred to as shallow (ST), and 20 cm, referred to as deep (DT)] was conducted on a Lihen sandy loam soil in spring 2007 at the Agricultural Research Service (ARS) irrigated research farm near Williston, North Dakota. Soil bulk density (ρb), gravimetric water content (θw), and saturated hydraulic conductivity (Ks) were measured three times during the growing season at four depth increments to 40 cm deep. Samples were taken approximately 0.5 m apart within the crop row of irrigated sugarbeet. Soil air-filled pore volume (εa) was calculated from soil bulk density and water content data. Soil penetration resistance (PR) was also measured in 2.5-cm increments to a depth of 35 cm. Roots were hand-harvested from each plot, and each sample consisted of the roots within an area consisting of two adjacent rows 1.5 m long. Soil ρb was greater in ST than in DT, whereas Ks was greater with DT than with ST. Soil PR was significantly greater in ST than in DT at the 0- to 20-cm depth. Soil θw and εa were slightly greater in DT than those under ST. Although tillage depth had no significant effect on sugarbeet population, root yield, or sucrose content, a small difference in sucrose yield between two depths of tillage may be attributed to reduced ρb, increased water intake, improved aeration, and increased response to nitrogen uptake under DT than under ST. It was concluded that tillage depth enhanced soil physical quality and had little effect on sugarbeet yield or quality.

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.

Estimation of CO2 diffusion coefficient at 0-10 cm depth in undisturbed and tilled soils

Diffusion coefficients (D) of CO2 at 0–10 cm layers in undisturbed and tilled soil conditions were estimated using the Penman (Penman HL. 1940. Gas and vapor movement in soil, 1. The diffusion of vapours through porous solids. J Agric Sci. 30:437–463), Millington–Quirk (Millington RJ, Quirk JP. 1960. Transport in porous media. In: Van Baren FA, editor. Transactions of the 7th International Congress of Soil Science. Vol. 1. Amsterdam: Elsevier. p. 97–106), Ridgwell et al. (Ridgwell AJ, Marshall SJ, Gregson K. 1999. Consumption of atmospheric methane by soils: A process-based model. Global Biogeochem Cy. 13:59–70), Troeh et al. (Troeh FR, Jabro JD, Kirkham D. 1982. Gaseous diffusion equations for porous materials. Geoderma. 27:239–258) and Moldrup et al. (Moldrup P, Kruse CW, Rolston DE, Yamaguchi T. 1996. Modeling diffusion and reaction in soils: III. Predicting gas diffusivity from the Campbell soil–water retention model. Soil Sci. 161:366–375) models. Soil bulk density and volumetric soil water content (θv) at 0–10 cm were measured on 14 April, 2 June and 12 July 2005 at 0–10 cm depth in no-till (NT) and conventional till (CT) malt barley and undisturbed soil grass–alfalfa (UGA) systems. Air-filled porosity (ε) was calculated from total soil porosity and θv measurements. Both soil air porosity and estimated CO2 diffusivity at the 0–10 cm depth were significantly affected by tillage. Results of CO2 diffusion coefficients in the soil followed trends similar to those for soil ε data. The CT tended to have significantly greater estimated soil CO2 diffusion coefficients than the NT and UGA treatments. The relationship between D/D 0, and air-filled porosity was well described by a power (R 2 = 0.985) function. The model is useful for predicting CO2 gas-diffusion coefficients in undisturbed and tilled soils at various ranges of ε where actual gas D measurements are time-consuming, costly and infeasible.

Long-term tillage influences on soil physical properties under dryland conditions in northeastern Montana

We evaluated the effect of long-term (>20 years) tillage (no-till [NT], spring till [ST], and fall and spring till [FST]) under continuous spring wheat on soil penetration resistance (PR), bulk density (ρb), water content (θm) and saturated hydraulic conductivity (Ks) under dryland cropping systems. Soil PR was significantly greater in the NT than in ST and FST treatments at 0–10 cm depth, but was greater in FST than in NT and ST at a depth deeper than 10 cm. Soil PR generally increased to a depth of 10–15 cm and then decreased beyond this depth. Long-term tillage reduced soil compaction in the surface (0–10 cm), but increased in the subsurface at a depth >10 cm due to the traffic intensity induced by tillage mechanism. Soil ρb was not affected by tillage and averaged 1.59, 1.58, and 1.61 Mg m−3 for NT, ST, and FST, respectively. Similarly soil θm was not influenced by tillage and generally decreased with increased intensity of soil manipulation and tillage frequency. Soil Ks generally decreased with increased tillage frequency. The results showed that soil ρb, θm, and Ks were minimally influenced by tillage intensity after 22 years of treatment imposition.

Tillage Effects on Dryland Soil Physical Properties in Northeastern Montana

We evaluated the effect of no tillage (NT) and conventional tillage (CT) on soil penetration resistance (PR), bulk density (BD), gravimetric moisture content (MC), and saturated hydraulic conductivity (Ks) during the fallow phase of a spring wheat–fallow rotation. The study was conducted on two soils mapped as Williams loam at the Froid and Sidney sites. Soil measurements were made on 19 May, 23 June, and 4 August 2005 at the Froid site and on 6 June and 8 July 2005 at the Sidney site. Tillage had no effect on either soil properties except on the PR at Sidney. However, soil PR, MC, and BD varied significantly with depth regardless of tillage and location. Further, soil PR and MC varied with the date of sampling at both locations, and PR generally increased with decreased MC at all soil depths. Soil Ks was slightly influenced by tillage at both locations.

Deficit Irrigation and Partial Rootzone Drying Compared in Fuji Apples: Fruit Yield, Fruit Quality and Soil Moisture Trends

Increase in competing demands for water from cities, recreational users, and nenvironmental groups are prompting the need to find new approaches to irrigation management that nmaintain yield, save water and reduce environmental degradation. The objective of this study was to nevaluate the impact of Deficit Irrigation (DI) and Partial Rootzone Drying (PRD) on apple yield and nsize as compared to a well-watered control (CI). Fuji apple trees received 609 mm, of irrigation in nthe CI; 385 mm in the DI; and 357 mm in the PRD per year averaged over the 2001, 2002 and 2003 ngrowing seasons. Fruit weight per tree was reduced by 10% in the DI treatment as compared to the nCI and PRD treatments. Also, the individual fruit size was reduced by 9.0% in the DI and 4.0% in the nPRD as compared to the CI treatment. However, the only statistically significant difference was nobserved in 2002 in which the CI’s fruit weight per tree was found to be greater than the DI. As for nfruit quality, the deficit irrigated treatments produced higher soluble solids and greater firmness than nthe control treatment. Finally, soil water content monitoring showed that more water was preserved nin the soil profile under PRD than under DI regime in 2001 and 2003 while the soil moisture in 2002 nwas nearly equal at the end of the growing season. This project demonstrated that a 35 to 45% nreduction in irrigation resulted in minimal apple yield and size reduction when implementing DI and nPRD irrigation strategies.

Pesticide Movement under Drip Chemigation: Model Simulations and Field Measurements

Soil pesticide samples were collected and analyzed from a field experiment under drip chemigation. Drip nchemigation of the systemic insecticide, imidacloprid, was used to protect muskmelon (cantaloupe) plants from cucumber nbeetles. After the efficacy in controlling the insect pest was determined, the finite element model LEWASTE was nconfigured to simulate: 1) drip chemigation of a pesticide in raised beds under plastic mulch, 2) advective/dispersive nmovement of pesticide from rainwater infiltration and drip irrigation, and 3) root extraction of pesticide with soil water. nThe model was executed using available input parameters to simulate soil distribution of pesticide during the period of nefficacy. A linear regression analyses between measured and predicted soil pesticide concentrations indicated a strong nrelationship between the model and the field study with a slope of 0.89, an intercept of –7.05 ppb and a r2 of 0.97. The nmodel and soil samples also showed that the pesticide, imidacloprid, did not leach during the time frame of evaluation and nthat 70% of the pesticide was still located in the root zone when efficacy ceased. In addition, the model simulated that nonly 11% of the applied pesticide was absorbed by the muskmelon plants during the period of efficacy. These results nsuggest that as the plants developed from 9 to 800 g, the muskmelons outgrew the source of the pesticide instead of the npesticide source being depleted for use by the plant via leaching, uptake, and degradation.