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Soil bulk density and moisture content are dynamic properties that vary with changes in soil and field conditions and have many agricultural, hydrological and environmental implications. The main objective of this study was to compare between a soil core sampling method (core) and the CPN MC-3 EliteTM nuclear gauge method (radiation) for measuring bulk density (ρB) and volumetric moisture content (θv) in a clay loam soil. Soil ρB and θv measurements were determined using the core and radiation methods at 0 - 10 and 10 - 20 cm soil depths. The mean values of soil ρB obtained using the core method (1.454, 1.492 g·cm−3) were greater than those obtained using the radiation method (1.343, 1.476 g·cm−3) at the 0 - 10 and 10 - 20 cm depths, respectively. Mean ρB and θv values averaged across both depths (referred to as the 0 - 20 cm depth) measured by the core method were 4.47% and 22.74% greater, respectively, than those obtained by the radiation method. The coefficients of variation (CV) of soil ρB values measured by the core method were lower than the CV values of those measured by the radiation method at both depths; however, the CV’s of ρB values for both methods were larger at the 0 - 10 cm depth than those measured at the 10 - 20 cm depth. Similarly, the CV values of soil θv values measured by the core method were lower than the CV values of those measured by the radiation method at both depths. There were significant differences between two methods in terms of ρB and θv, with the core method generating greater values than the radiation method at the 0 - 20 cm depth. These discrepancies between the two methods could have resulted from soil compaction and soil disturbance caused by the core and radiation techniques, respectively, as well as by other sources of error. Nevertheless, the core sampling method is considered the most common one for measuring ρB for many agricultural, hydrological and environmental studies in most soils.

Soil inorganic carbon (SIC) constitutes a large proportion of soil total carbon (STC) under dryland cropping systems in arid and semiarid regions. Information on the effect of management practices on SIC is scarce. We evaluated the effect of 1‐ to 4‐yr no‐till diversified crop rotations on SIC at the 0‐ to 120‐cm depth in Sidney and Friod, MT. The SIC increased from the soil surface to 90‐cm depth and then declined. Crop rotations did not affect SIC and STC, except at 90–120 cm in Sidney where barley (Hordeum vulgare L) and winter wheat (Triticum aestivum L) in rotation with pea (Pisum sativum L.) had higher SIC than other crop rotations. The SIC contributed from 0% of STC at 0–15 cm for most crop rotations to 78% at 60–90 cm for barley–pea rotation. Long‐term studies are needed to evaluate the effect of dryland crop rotations on SIC in the northern Great Plains.

Accounting of N inputs and outputs and N retention in the soil provides N balance that measures agroecosystem performance and environmental sustainability. Because of the complexity of measurements of some N inputs and outputs, studies on N balance in long-term experiments are scanty. We examined the effect of 8 years of tillage, crop rotation, and cultural practice on N balance based on N inputs and outputs and soil N sequestration rate under dryland cropping systems in the northern Great Plains, USA. Tillage systems were no-tillage (NT) and conventional tillage (CT) and crop rotations were continuous spring wheat (Triticum aestivum L.) (CW), spring wheat–pea (Pisum sativum L.) (W–P), spring wheat–barley (Hordeum vulgaris L.) hay–pea (W–B–P), and spring wheat–barley hay–corn (Zea mays L.)–pea (W–B–C–P). Cultural practices were traditional (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and improved (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height). Total N input due to N fertilization, pea N fixation, atmospheric N deposition, crop seed N, and nonsymbiotic N fixation was greater with W–B–C–P than CW, regardless of tillage and cultural practices. Total N output due to aboveground biomass N removal and N losses due to denitrification, volatilization, plant senescence, N leaching, gaseous N (NOx) emissions, and surface runoff were not different among treatments. Nitrogen sequestration rate at 0–20 cm from 2004 to 2011 varied from 29 kg N ha−1 year−1 in CT with W–P to 89 kg N ha−1 year−1 in NT with W–P. Nitrogen balance varied from − 39 kg N ha−1 year−1 in NT with CW and the improved practice to 41 kg N ha−1 year−1 in CT with W–P and the traditional practice. Because of legume N fixation and increased soil N sequestration rate, diversified crop rotations reduced external N inputs and increased aboveground biomass N removal, N flow, and N balance compared with monocropping, especially in the CT system. As a result, diversified legume–nonlegume crop rotation not only reduced the cost of N fertilization by reducing N fertilization rate, but also can be productive by increasing N uptake and N surplus and environmentally sustainable by reducing N losses compared with nonlegume monocropping, regardless of cultural practices in dryland agroecosystems.

Diversified crop rotation and management strategies may affect crop water and N productivity. We studied the effect of tillage, crop rotation, and management system on pre-plant and postharvest soil water storage, annualized crop yield, water use, and water and N productivity from 2005 to 2010 in the northern Great Plains, USA. Tillage were conventional tillage and no-tillage; crop rotations were continuous spring wheat (Triticum aestivum L.) (CW), spring wheat-pea (Pisum sativum L.) (WP), spring wheat-forage barley (Hordeum vulgare L.)-pea (WBP), and spring wheat-forage barley-corn (Zea mays L.)-pea (WBCP). Managements were traditional (a combination of recommended seeding rate, broadcast N fertilization, early planting, and short stubble height) and alternate (a combination of increased seeding rate, banded N fertilization, late planting, and tall stubble height) systems. Aboveground biomass was 16–85%, preplant soil water 23–118%, postharvest soil water 38–246%, and water productivity 28–61% greater with WBCP than CW in 3 out of 6 yr. Crop water use and biomass N accumulation varied with tillage, crop rotations, and management systems in various years. Grain yield was 26–41% and grain water productivity 25–32% lower with WBP than other crop rotations. Grain N accumulation was 20–52%, grain N productivity 23–60%, and grain and biomass N removal indices 18–153% greater with WP than CW and WBCP, but biomass N productivity was 98–110% lower with CW than other crop rotations. Diversified crop rotation with longer rotation length increased crop yield, soil water storage, and water productivity, but shorter rotation with legume increased grain and biomass N productivity and N removal.

Nitrogen balance provides a measure of agroecosystem performance and environmental sustainability by taking into accounts of N inputs and outputs and N retention in the soil. The objective of this study was to evaluate N balance based on N inputs and outputs and soil N sequestration after 7 yr in response to five dryland crop rotations (two 4-yr stacked and two 4-yr alternate-year rotations and one monocropping) and two cultural practices arranged in a split-plot design in the northern Great Plains, USA. Stacked rotations were durum ( Triticum turgidum L.)-durum-canola ( Brassica napus L.)-pea ( Pisum sativum L.) (D-D-C-P) and durum-durum-flax ( Linum usitatissimum L.)-pea (D-D-F-P). Alternate-year rotations were durum-canola-durum-pea (D-C-D-P) and durum-flax-durum-pea (D-F-D-P). Monocroppping was continuous durum (CD). Cultural practices were traditional (conventional till, recommended seed rate, broadcast N fertilization, and reduced stubble height) and ecological (no-till, increased seed rate, banded N fertilization, and increased stubble height). Total annual N input due to N fertilization, pea N fixation, atmospheric N deposition, crop seed N, and nonsymbiotic N fixation was lower in CD than other crop rotations, regardless of cultural practices. Total N output due to crop grain N removal and N losses due to denitrification, volatilization, plant senescence, N leaching, gaseous N (NO x ) emissions, and surface runoff was lower in traditional CD and D-F-D-P than traditional D-C-D-P and ecological D-C-D-P, D-D-C-P, and D-F-D-P. Nitrogen sequestration rate at 0–125 cm from 2005 to 2011 ranged from 40 kg N ha −1 yr −1 for ecological D-D-F-P to 52 kg N ha −1 yr −1 for ecological CD. Nitrogen balance ranged from −39 to −36 kg N ha −1 yr −1 with CD compared to 9–25 kg N ha −1 yr −1 with other crop rotations in both cultural practices. Because of reduced reliance on external N inputs and increased grain N removal, N flow, and N surplus, crop rotations with legumes, nonlegumes, and oilseed crops in the rotation can be productive and environmentally sustainable compared with monocropping, regardless of cultural practices.

One of today’s greatest challenges of irrigated agriculture is to produce more food and fiber with less water, which can be accomplished by maximizing crop water productivity (CWP). A study was conducted to evaluate and compare the effect of conventional tillage (CT) and strip tillage (ST) on crop water use (CWU) and CWP of sugarbeet (Beta vulgaris L.) on clay loam soil in the northern Great Plains (NGP). Seasonal CWU and CWP for sugarbeet root and sucrose yields were determined for the 2006, 2007, and 2008 growing seasons according to the water balance and CWP equations under CT and ST practices. No significant differences due to tillage were found for CWU of sugarbeet. In 2006, CWP for root yield was significantly greater in ST relative to CT due to wind damage early in the spring which reduced sugarbeet plant population in the CT. The mean CWP for root yield across three growing seasons was10% greater for ST than for CT due to the protected soil–plant environment under the ST. The ST greatly reduces wind erosion and the related plant damage. The ST system used 0.0093 m³ and 0.061 m³ of irrigation water less than CT system to produce 1 kg of sugarbeet root and 1 kg of sucrose yield, respectively, throughout the growing season. We concluded that ST can be used to produce sugarbeet root yield and CWP comparable to CT or even in some instances greater than CT in areas that are prone to wind damage to sugarbeet seedlings.

Published in Agron. J. 105:37–50 (2013) doi:10.2134/agronj2012.0203 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. S wheat (Triticum aestivum L., excluding durum wheat) was harvested on 5.35 million ha of croplands in the United States in 2011, with 89.1% occurring in the northern Great Plains (NGP) states including North Dakota, Montana, Minnesota, and South Dakota. Montana had the highest percentage of spring wheat acreage (31.3%) among all spring wheat production states (National Agricultural Statistics Service, 2011a). Th e 2007 Census of Agriculture showed that about half of the spring wheat acreage in Montana was under a continuous spring wheat production system, while the other half was in a 2-yr spring wheat–fallow system. Most of this spring wheat area (95.4%) was rainfed (National Agricultural Statistics Service, 2007). Th e lack of available water for crop growth is the primary factor aff ecting dryland spring wheat production in the NGP. A spring wheat yield trial conducted at Sidney, MT, with >70 cultivars during 2005 to 2009 showed that the yield of dryland wheat was about 30% less than that of the irrigated crop (J. Eckoff , personal communication, 2010). Brown et al. (1981) reported that spring wheat yield increased 135 kg ha–1 with every centimeter increase in plant water use in Montana and North Dakota. A similar relationship between spring wheat yield and plant-available water was also found in the inland Pacifi c Northwest (Schillinger et al., 2008). Winter wheat yields in the central Great Plains increased by 141 kg ha–1 for every centimeter increase in plant-available water in the soil at planting (Nielsen et al., 2002) and by 125 kg ha–1 for every centimeter of water uptake aft er 13 cm of water use (Nielsen et al., 2011). Various management strategies have been proposed and applied to cope with soil water shortage for dryland spring wheat production in the NGP, including no-till and reduced tillage with residue mulching and crop rotations. Fenster (1973) reported that the soil water storage effi ciency increased from 16 to 31% in Montana by adding surface residue cover during summer fallow. Nielsen and Vigil (2010) reported that precipitation storage effi ciency during the fallow period of a winter wheat–fallow system increased from 20% with conventional tillage fallow management to 35% for no-till management in Colorado. In general, a higher percentage of residue cover would lead to higher soil water storage (Tanaka and Aase, 1987). Lenssen et al. (2007) documented that zero tillage oft en provided higher soil water content at planting; however, Deibert et al. (1986) found that a diff erence in water storage between no-till and tilled fi eld in North Dakota was not evident ABSTRACT

Information is needed on novel management practices to increase dryland C sequestration and soil quality in the northern Great Plains, USA. We evaluated the effects of tillage, crop rotation, and cultural practice on dryland crop biomass (stems and leaves) yield, surface residue, and soil C fractions at the 0 - 20 cm depth from 2004 to 2008 in a Williams loam in eastern Montana, USA. Treatments were two tillage systems (no-tillage [NT] and conventional tillage [CT]), two crop rotations (continuous spring wheat [Triticum aestivum L.] [CW] and spring wheat-barley [Hordeum vulgaris L.] hay-corn [Zea mays L.]-pea [Pisum sativum L.] [W-B-C-P]), and two cultural practices (regular [conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height] and ecological [variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height]). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Crop biomass was 24% to 39% greater in W-B-C-P than in CW in 2004 and 2005. Surface residue C was 36% greater in NT than in CT in the regular practice. At 5 - 20 cm, SOC was 14% greater in NT with W-B-C-P and the regular practice than in CT with CW and the ecological practice. In 2007, POC and PCM at 0 - 20 cm were 23% to 54% greater in NT with CW or the regular practice than in CT with CW or the ecological practice. Similarly, MBC at 10 - 20 cm was 70% greater with the regular than with the ecological practice in NT with CW. Surface residue, PCM, and MBC declined from autumn 2007 to spring 2008. No-tillage with the regular cultural practice increased surface residue and soil C storage and microbial biomass and activity compared to conventional tillage with the ecological practice. Mineralization reduced surface residue and soil labile C fractions from autumn to spring.

Land use and management practices may influence plant C inputs and soil CO 2 emission. We evaluated the effect of a combination of irrigation, tillage, cropping system, and N fertilization on plant biomass C, soil temperature and water content at the 0- to 15-cm depth, and CO 2 emission in a sandy loam soil from April to October, 2006 to 2008, in western North Dakota. Treatments were two irrigation practices (irrigated and unirrigated) and six cropping systems (conventional-tilled malt barley [Hordeum vulgare L.] with N fertilizer [CTBFN], conventional-tilled malt barley with no N fertilizer [CTBON], no-tilled malt barley-pea [Pisum sativum L.] with N fertilizer [NTB-PN], no-tilled malt barley with N fertilizer [NTBFN], no-tilled malt barley with no N fertilizer [NTBON], and no-tilled Conservation Reserve Program [NTCRP]). Plant biomass C was greater in NTBFN than in NTBON in 2006 and 2007 but was greater in NTB-PN than in CTBON, NTBON, or NTCRP in 2008. Soil temperature was greater but water content was lower in NTCRP than in CTBFN and NTBFN. Soil CO 2 flux peaked immediately following heavy rain or irrigation (> 15 mm). Total CO 2 ftux from April to October was greater in the irrigated than in the unirrigated practice and greater in NTCRP than in annual cropping systems. Soil CO 2 emission was probably related more to soil temperature and water content or tillage than to aboveground plant C input. Because of reduced CO 2 flux compared with CTBON and NTCRP but similar biomass yield as NTBFN and CTBFN, NTB-PN may be used to reduce CO 2 emission from croplands in the northern Great Plains.

Novel management practices are needed to increase dryland soil organic matter and crop yields that have been declining due to long-term conventional tillage with spring wheat (Triticum aestivum L.)-fallow system in the northern Great Plains, USA. The effects of tillage, crop rotation, and cultural practice were evaluated on dryland crop biomass (stems + leaves) yield, surface residue, and soil organic C (SOC) and total N (STN) at the 0–20 cm depth in a Williams loam (fine-loamy, mixed, superactive, frigid, Typic Argiustolls) from 2004 to 2007 in eastern Montana, USA. Treatments were two tillage practices [no-tillage (NT) and conventional tillage (CT)], four crop rotations [continuous spring wheat (CW), spring wheat-pea (Pisum sativum L.) (W-P), spring wheat-barley (Hordeum vulgaris L.) hay-pea (W-B-P), and spring wheat-barley hay-corn (Zea mays L.)-pea (W-B-C-P)], and two cultural practices [regular (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and ecological (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height)]. Crop biomass and N content were 4 to 44% greater in W-B-C-P than in CW in 2004 and 2005 and greater in ecological than in regular cultural practice in CT. Soil surface residue amount and C and N contents were greater in NT than in CT, greater in CW, W-P, and W-B-C-P than in W-B-P, and greater in 2006 and 2007 than in 2004 and 2005. The SOC and STN concentrations at 0–5 cm were 4 to 6% greater in CW than in W-P or W-B-P in NT and CT from 2005 and 2007. In 2007, SOC content at 10–20 cm was greater in W-P and W-B-P than in W-B-C-P in CT but STN was greater in W-B-P and W-B-C-P than in CW in NT. From 2004 to 2007, SOC and STN concentrations varied at 0–5 cm but increased at 5–20 cm. Diversified crop rotation and delayed planting with higher seed rates and banded N fertilization increased the amount of crop biomass returned to the soil and surface residue C and N. Although no-tillage increased surface residue C and N, continuous nonlegume cropping increased soil C and N levels at the surface layer compared with other crop rotations. Continued return of crop residue from 2004 to 2007 may increase soil C and N levels but long-term studies are needed to better evaluate the effect of management practices on soil C and N levels under dryland cropping systems in the northern Great Plains.

Soil Sci. Soc. Am. J. 73:1488-1495doi:10.2136/sssaj2008-0405Received 9 Dec. 2008.*Corresponding author (upendra.sainju@ars.usda.gov).© Soil Science Society of America677 S. Segoe Rd. Madison WI 53711 USAAll rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Access to real-time information on soil chemistry would assist farmers in making decisions about nutrient management. Hand held Ion Selective Electrodes (ISE) are commercially available for testing pH, sodium (Na), potassium (K), and nitrate-nitrogen (NO3-N). To date, there has been some success in adapting hand held ISE devices for testing plant sap nutrient levels. The objective of our study was to determine if these devices could be used to directly measure ion content in soils. Two different soils, a Quincy sand and a Warden silt loam, made into slurries by adding water to achieve 50, 40, 30, 27.5, 25, 22.5, 20, 17.5, or 15% soil water content by volume. The slurries were directly applied to the hand held ISE (Cardy meter) five times for each soil texture and moisture content. In addition, soil solution was also sorbed onto absorbent paper and the paper placed directly on the Cardy meter surface. The results were compared to soil NO3-N, K, Na, and pH determined by conventional methods. The ha...

Eighteen pan lysimeters were installed at a depth of 1.2 m in a Hagerstown silt loam soil in a corn field in central Pennsylvania in 1988. In 1995, wick lysimeters were also installed at 1.2 m depth in the same access pits. Treatments have included N fertilizer rates, use of manure, crop rotation (continuous corn, corn-soybean, alfalfa-corn), and tillage (chisel plow-disk, no-till). The leachate data were used to evaluate a number of nitrate leaching models. Some of the highlights of the 11 years of results include the following: 1) growing corn without organic N inputs at the economic optimum N rate (EON) resulted in NO3–-N concentrations of 15 to 20 mg l-1in leachate; 2) use of manure or previous alfalfa crop as partial source of N also resulted in 15 to 20 mg l-1of NO3–-N in leachate below corn at EON; 3) NO3–-N concentration in leachate below alfalfa was approximately 4 mg l-1; 4) NO3–-N concentration in leachate below soybeans following corn was influenced by fertilizer N rate applied to corn; 5) the mass of NO3–-N leached below corn at the EON rate averaged 90 kg N ha-1(approx. 40% of fertilizer N applied at EON); 6) wick lysimeters collected approximately 100% of leachate vs. 40–50% collected by pan lysimeters. Coefficients of variation of the collected leachate volumes for both lysimeter types were similar; 7) tillage did not markedly affect nitrate leaching losses; 8) tested leaching models could accurately predict leachate volumes and could be calibrated to match nitrate leaching losses in calibration years, but only one model (SOILN) accurately predicted nitrate leaching losses in the majority of validation treatment years. Apparent problems with tested models: there was difficulty estimating sizes of organic N pools and their transformation rates, and the models either did not include a macropore flow component or did not handle macropore flow well.

The simulation accuracies of five water quality models, LEACHW, MACRO, NCSWAP, SLIM, and SOIL to predict the amount of drainage water were evaluated and compared to field data from a 5-yr leaching experiment. The study was conducted on Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalf). Drainage fluxes below the rooting zone of corn were measured with pan lysimeters in 1988-1989, 1989-1990, 1990-1991, 1991-1992, and 1992-1993. A series of 18 zero-tension pan lysimeters (0.465 m 2 area) were installed at a depth of 1.2 m to collect drainage water at approximately the rooting depth of corn. All five models were calibrated to the site conditions using data from 1989 to 1990. The calibrated inputs were then used to evaluate the models' simulating accuracy using 1988-1989, 1990-1991, 1991-1992, and 1992-1993 drainage data. The cumulative annual simulations of drainage water from each model were compared to the mean of pan efficiency corrected measured data for these five sampling years. Simulated results for all five models fell within 95% confidence intervals of the measured data. Validation simulations of drainage fluxes were about as accurate as calibration simulations. The statistical analyses indicated that all five models performed well and have the potential to accurately predict the amount of drainage fluxes below the 1.2 m depth under corn cropping system without the need to calibrate the model for each year. There were small differences among the overall performances of the models for simulating drainage losses, but these differences were not significant using one-way analysis of variance.

The accuracy of the Nitrogen and Carbon cycling in Soil, Water And Plant (NCSWAP) model to simulate (nitrate-nitrogen) NO 3 -N leaching from orchardgrass (Dactylis glomerata L.) pasture was evaluated using data collected from a 3-yr leaching experiment conducted in central Pennsylvania on Hagerstown silt loam soil (fine, mixed, mesic, Typic Hapludalf). Nitrate leaching losses below the 1-m depth from N-fertilized orchardgrass sod were measured with intact soil core lysimeters (0.6-m diam. by 1-m long). Five N-fertilizer treatments consisted of a control, urine application in the spring, urine application in the summer, urine application in the fall, and feces application in the summer were used to test the model. The model was calibrated using the data from 1993 to 1994 and then was validated using 1994 to 1995 and 1995 to 1996 water flow- and NO 3 -N leaching data. Statistical analysis indicated a good fit between field measured and predicted NO 3 -N leaching for most treatments in each year. The model simulations of water flow- and NO 3 -N leaching losses below the 1-m depth were compared with the mean of measured field data for these 3 yr. The results of this study showed that the NCSWAP model performed well and accurately simulated water flow and total annual NO 3 -N loss through leaching below the 1-m depth under orchardgrass pasture. However, the model failed to produce accurate simulations for the feces treatment in 1994 to 1995. The simulation error in the feces treatment seemed to be related to N mineralization process in the model. Generally, the results of this study suggest that the NCSWAP model can be used for predicting NO 3 -N leached annually from pastured orchardgrass.

The ability of the N submodel, LEACHN, of the Leaching Estimation And CHemical Model (LEACHM model) to simulate nitrate-nitrogen (NO 3 -N) leaching from orchardgrass (Dactylis glomerata L.) pasture was evaluated using field data from a 2-yr experiment. Leaching data were collected from an experiment conducted in central Pennsylvania on Hagerstown silt loam soil (fine, mixed, mesic, Typic Hapludalf). Nitrate losses below the 1-m depth from N-fertilized orchardgrass sod were measured with intact soil core lysimeters (0.6-m diam. by 1-m long). Five N fertilizer treatments consisted of a control, urine application in the spring, urine application in the summer, urine application in the fall, and feces application in the summer. Calibration N transformation rate constants from previous work with inorganic fertilizer and manure treatments under corn were used to evaluate the LEACHN model under pasture conditions. Statistical analysis indicated that the model accurately predicted annual NO 3 -N leaching below the 1-m depth for three to five of the five treatments in each year. The model failed to produce accurate predictions for the control and feces treatments in 1993 to 1994. The simulation error in these two treatments appeared to be related to soil N transformation rate constants in the model. Other reasons for discrepancies between measured and simulated NO 3 -N leaching for some months may have been due to restricted water flow associated with frozen soil or a heavy snowpack during winter. Results demonstrate the potential of the LEACHN model to predict NO 3 -N leaching under pasture conditions using N transformation rate constants determined through the calibration process from corn (Zea mays L.) fields on similar soils.

The abilities of the Richards and convection-dispersion equations approach (LEACHNR) and the capacity model approach (LEACHNA) of the nitrogen version (LEACHN) of the LEACHM model to simulate nitrate leaching were evaluated using field data from a 5-year nitrate leaching experiment conducted in central Pennsylvania on Hagerstown silt loam soil (fine, mixed, mesic, Typic Hapludalf). Nitrate leaching losses from N-fertilized and manured corn below the 1.2-m depth were measured with zero-tension pan lysimeters. Three N-fertilized and manured treatments for 1988-1989, 1989-1990, and 1990-1991 and two N-fertilized treatments for 1991-1992 and 1992-1993 were used from the leaching experiment to evaluate both approaches of LEACHN. The individual monthly simulations of nitrate leaching were compared with the mean of pan efficiency corrected-measured data for these 5 years. Both approaches of the model were calibrated to the site conditions using the data of 1989-1990 and were then evaluated using 1988-1989, 1990-1991, 1991-1992 and 1992-1993 nitrate leaching data. Simulated results for the calibration year for both models were reasonably accurate (31 of 36 months simulated within the experimental 95% confidence limits). The statistical analysis used in this study indicated that both LEACHNA and LEACHNR adequately (91 to 120 months within the 95% confidence limits) predicted nitrate leaching below the 1.2-m depth for treatments in the refinement years. Much of the simulation error in some treatments in the refinement years seemed to be related to the sub-routine controlling soil nitrogen transformation processes and their rate constants in the model. The large deviations in NO 3 - -N leached in some winter months may be related, in part, to problems with simulated water flow associated with the frozen soil conditions and snow accumulation. The addition of a dual-pore water flow option (LEACHNA) to the nitrogen version of LEACHM did not improve prediction of nitrate leaching beyond the rooting zone of corn under Pennsylvania conditions.

Agricultural system models are useful tools to synthesize field experimental data and to extrapolate the results to longer periods of weather and other cropping systems. The objectives of this study were: 1) to quantify the effects of crop management practices and tillage on soil water and spring wheat production in a continuous spring wheat system using RZWQM2 model under a dryland condition, and 2) to extend the results to longer term weather conditions and alternate cropping systems and management practices. Measured soil water content, crop yield, and total above ground biomass under different tillage and plant management practices were used to calibrate and validate the RZWQM2 model. The model showed inevident impacts of tillage and significant reduction in grain yield and biomass under late planting, in agreement with observed differences among treatments. The hydrologic analysis under long-term climate variability showed a large water deficit (32.3 cm) for the spring wheat crop; Fallowing the dryland every other year conserved 4.2 cm water for the following wheat year, of which only 1.7 cm water was taken up by wheat, resulting in a yield increase of 249 kg ha-1 (13.7%). However, the annualized average total yield decreased 782 kg ha-1 (43.1%) due to one year fallow; thus the spring wheat-fallow rotation was not economical. Other long-term simulations showed that optimal planting dates ranged from March 1 to April 10, and the seeding rate with optimum economic return was 3.71 and 3.95 × 106 seeds ha-1 for conventional and ecological management treatments, respectively.

Leaching of agricultural chemicals from the root and vadose zones into groundwater is an important environmental concern. To procure a better understanding of the movement and transport of agricultural chemicals through the soil profile, a field research study was conducted to estimate bromide leaching losses under saturated conditions where preferential flow is occurring. The field data were then used to evaluate the LEACHM model. Eighteen double-ring infiltrometers were used to apply a pulse (100 mm depth) of bromide tracer on two previously saturated soils located in a karst region of southeastern Pennsylvania. Internal drainage over the next seven days resulted in nearly 51% of the applied Br − being leached to a depth below 0.80 m. The LEACHM model was used to simulate the amount of bromide leached in each infiltrometer. The model predicted, accurately, an average of 46% of the applied Br − leached below the 0.80 m depth. Mean values of bromide concentration in the soil profile were predicted within two standard deviations of the measured mean for all depths except for the 0.20–0.40 m depth increment where the model overpredicted the bromide concentration. The model predictions of Br − leached were tested against field measurements using several statistical tests. The LEACHM model performed adequately under preferential flow conditions, perhaps because the infiltration rate at each site was used as a model input. This, actually, is some measure of the macropore flow process and suggests that simple models such as LEACHM can be used in the field, as long as a distribution of infiltration rates is used as an input.

[1] Preferential flow path development in the field is the result of the complex interaction of multiple processes relating to the soil's structure, moisture condition, stress level, and biological activity. Visualizing and characterizing the cracking behavior and preferential paths evolution with soil depth has always been a key challenge and a major barrier against scaling up existing hydrologic concepts and models to account for preferential flows. This paper presents a new methodology to quantify soil preferential paths in the field using liquid latex. The evolution of the preferential flow paths at different soil depths and moisture conditions is assessed. Results from different soil series (Savage clay loam soil versus Chalmers clay loam) and different vegetation covers and soil managements (corn/tilled field versus soybean no-till field in the Chalmers soil series) are presented.

The LEACHM model was evaluated using data from a field experiment conducted in Lancaster County, Pennsylvania, U.S.A. Many of the parameter input values were the means of determinations for soil samples from the field site. Measured nitrogen (N) uptake and nitrate (NO3-N) storage in the soil profile, as well as mineralization and nitrification rates were higher in 1987 than in 1988. The measured N removal by crops was taken as the simulated N uptake. A reasonably good agreement between simulated and measured values was obtained for NO3-N storage. However, higher rate constants had to be used for 1987 than for 1988 in order to match simulated with measured storage. The simulated soil solution NO3-N concentrations at 1.2-m depth agreed quite well with those measured in porous cup water samples, except for the highest ammonium nitrate treatment. In general, the simulation results indicated that the LEACHM model described the nitrogen dynamics fairly well.

Since laboratory and field measurement of soil hydraulic properties is time consuming and subject to large error, numerous models have been proposed to predict soil hydraulic properties from easily measurable soil properties such as particle size distribution, bulk density, effective porosity and carbon content. In this study a multiple linear regression model was developed to predict the saturated hydraulic conductivity of soils from their particle size distribution and bulk density data. Published data from 350 soil core samples of varying soils from different sources were used to develop the model. Stepwise regression selected the best model for prediction of soil hydraulic conductivity (R2 = 0.68, P < 0.0001) from the independent parameters of silt, clay, and bulk density. Additional field measured data were collected to test and validate the model using several statistical evaluation procedures. Based on the statistical evaluation criteria, the model performed fairly well and gave a satisfactory validation versus the field measured data.

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.

Among greenhouse gases, carbon dioxide (CO(2)) is one of the most significant contributors to regional and global warming as well as climatic change. A field study was conducted to (i) determine the effect of soil characteristics resulting from changes in soil management practices on CO(2) flux from the soil surface to the atmosphere in transitional land from perennial forages to annual crops, and (ii) develop empirical relationships that predict CO(2) flux from soil temperature and soil water content. The CO(2) flux, soil temperature (T(s)), volumetric soil water content (theta(v)) were measured every 1-2 weeks in no-till (NT) and conventional till (CT) malt barley and undisturbed soil grass-alfalfa (UGA) systems in a Lihen sandy loam soil (sandy, mixed, frigid Entic Haplustoll) under irrigated and non-irrigated conditions in western North Dakota. Soil air-filled porosity (epsilon) was calculated from total soil porosity and theta(v) measurements. Significant differences in CO(2) fluxes between land management practices (irrigation and tillage) were observed on some measurement dates. Higher CO(2) fluxes were detected in CT plots than in NT and UGA treatments immediately after rainfall or irrigation. Soil CO(2) fluxes increased with increasing soil moisture (R(2)=0.15, P0.01) while an exponential relationship was found between CO(2) emission and T(s) (R(2)=0.59). Using a stepwise regression analysis procedure, a significant multiple regression equation was developed between CO(2) flux and theta(v), T(s) (CO(2) flux = e(-3.477+0.123T(s)+6.381theta)(v); R(2)=0.68, Por= 0.01). Not surprisingly, soil temperature was a driving factor in the equation, which accounted for approximately 59% in variation of CO(2) flux. It was concluded that less intensive tillage, such as no-till or strip tillage, along with careful irrigation management will reduce soil CO(2) evolution from land being converted from perennial forages to annual crops.