Pachic Haplustoll Research Articles

Influence of management systems on the nitrogen mineralization and fertilization of sugarcane

In Colombia, nitrogen fertilizer recommendations for sugarcane are based on data obtained with the WalkLey & Black method, but they do not always result in the best yield. In this sense, the present study aimed to compare the results of the determination of fast mineralizable nitrogen (amino sugars), performed with the Illinois Soil Nitrogen test (ISNT) and Direct Steam Distillation method (DSD) for nitrogen recommendations for crops. A complete randomized block design was used with six treatments, adding nitrogen through urea and compost to Pachic haplustoll soils in Valle del Cauca with organic and conventional production systems that were evaluated from 2011 to 2014. The results showed that higher nitrogen mineralization was estimated using ISNT and DSD methodologies than with the Walkley-Black method, and that its content was different depending on the management system. The best methodology that quantified mineralizable N was Direct Steam Distillation (DSD); however for conventional systems sugarcane was Illinois Soil Nitrogen Test (ISNT), showing differences for the variables associated with the production and yield between the tested systems.

Fine and Coarse Scale Sampling of Spatial Variability within a Switchgrass Field in Oklahoma

Aim: The objective of this study was to describe the spa tial patterns of selected soil properties and biomass yield at fine and coarse scale in a switchgrass field to determine the appropriate sampling approach to enable the calculation of means with minimum variance. Methodology: Spatial variability of biomas s yield and soil properties at fine (2.5 m sampling interval) and coarse (10 m sampling interval) scales were assessed through semivariogram analysis. The site located in Chickasha, Oklahoma, consisted of two soil types a Dale silt loam (fine - silty, mixed, superactive, thermic Pachic Haplustolls) and McLain silty clay loam (fine, mixed, superactive, thermic Pachic Argiustolls). Eighty soil samples were collected along two 100 m transects at 2.5 and 10 m intervals established across each soil type in both 20 12 and 2013. Results: The semivariograms revealed coarse scale organic carbon (OC) to be strongly correlated with range values from 56 – 78 m for both soils. Normalized difference vegetative index (NDVI) was

In Vitro Digestibility and Chemical Composition of Kikuyugrass as Influenced by Soil Silicon, Liming, and Genotype

Kikuyugrass (Pennisetum clandestinum Hochst. ex Chiov.) is an active silicon (Si) accumulator, and Si can reduce the organic‐matter digestibility of forage grasses. Calcium carbonate (crushed coral) applications to a low Si Maile silt loam soil (Acrudoxic Hydrudands) had no effect on the in vitro digestible organic matter (IVDOM) concentration of 3‐week‐old (4.5‐leaf‐per‐tiller stage of development) ‘Whittet’ kikuyugrass regrowth, whereas calcium silicate (wollastonite) applied at the calcium equivalent of the calcium carbonate rates produced a curvilinear (crescent‐shaped quadratic) IVDOM response. Whittet IVDOM decreased when grass Si concentration exceeded about 22 g kg−1 or when 0.5 M acetic acid–extractable soil Si exceeded about 230 mg kg−1. Common and ‘Hosaka’ kikuyugrass regrowth on the Maile soil had less Si and greater IVDOM concentrations than those observed for high‐Si Kohala (Humic Dystrustepts) and Waialua (Pachic Haplustolls) silty clay soils. Whittet had greater crude protein and IVDOM concentrations and lesser fiber concentrations than common.

Relationships between Immobilized Phosphorus Uptake in Two Grain Legumes and Soil Bioactive Phosphorus Pools in Fertilized and Manure‐Amended Soil

Mixing P‐immobilizing additives with manure has raised concerns of irreversible reduction in P availability to growing crops. A potted plant growth experiment was conducted to characterize cattle manure P mineralization as modified by iron amendments and uptake by pigeon pea (Cajanus cajan L. Millsp.) and soybean [Glycine max (L.) Merr.]. Triple superphosphate, untreated, or manure amended with Fe at 1:1 or 1:3 molar ratio of manure P:Fe, was applied to Dale silt loam (fine‐silty, mixed, superactive, thermic Pachic Haplustolls) at the rate of 20 mg kg−1. Whole plants were harvested at three stages of development (vegetative, flowering, and physiological maturity) to determine and correlate P uptake to changes in soil bioactive P pools over the growing season. Dry matter production was unaffected by Fe at both application rates. Phosphorus solubility and plant uptake were reduced at the 1:3 P:Fe molar ratio rate, in spite of the legumes' reported ability to secrete siderophores. Within‐season changes in bioactive P fractions indicated that P was taken up from the inorganic (water‐extractable P [WEP] + inorganic ligand‐exchangeable P [EEPi]) pools. Comparing soil P pools in cropped and noncropped soils, the decrease in the organic phosphohydrolase‐labile P (PHP) pool corroborated the fact that the PHP pool replenished the WEP + EEPi fractions. Although Mehlich 3 P and EEPi were related, the Mehlich 3 P pool showed no significant relationship with whole plant or any plant part P. The latter did not perform as well as the EEPi pool in assessing plant availability and enzymatically mediated turnover of immobilized P.

RESPONSE OF SELECTED SOIL PHYSICAL AND HYDROLOGIC PROPERTIES TO MANURE AMENDMENT RATES, LEVELS, ANDTYPES

Manure amendments affect several soil physical and hydrologic properties. The objectives of this study were to evaluate the effect of (i) manure amendment rates (0, 168, 336, and 672 kg total N ha -1 ), levels (one-time application, and two-time application), and types (chicken manure [CM], dairy manure [DM], and swine manure [SM]) on bulk density (ρ b ), total soil porosity (θ t ), and saturated hydraulic conductivity (K sat ) of a highly weathered tropical soil (Waialua gravely clay variant, isohyperthermic Pachic Haplustolls) and (ii) measuring instruments (tension infiltrometer [TI] and double-ring infiltrometers [DR]) on K sat . For the two-time application level, all the plots received additional manure to compensate for the amounts decomposed during the first growing season. The field was tilled to the top 15-cm depth before and after manure application during the two growing seasons. Measurements of ρ b and θ t were conducted on undisturbed soil core samples collected from the top 10 cm of soil from a field cultivated with sweet corn (Zea mays L. subsp. mays) and irrigated with a drip irrigation system for two consecutive growing seasons. Saturated hydraulic conductivity was calculated from steady state infiltration rates measured with TI and DR. Results show that the increased manure amendment rates and levels significantly (P < 0.01) decreased ρ b and consequently increased θ t . The values of K sat increased significantly (P < 0.01) with increase in CM and DM amendment rates and levels. For SM treatments, the values of K sat decreased with increase in manure amendment rates and levels; these results concur with those reported in literature on liquid manures. Saturated hydraulic conductivity calculated from DR data was slightly greater than that from TI data for CM and DM treatments. Opposite results were found for SM treatments. However, a good agreement (R2 = 0.90) was observed between K sat values calculated from TI and DR data across treatments. We conclude that the CM and DM amendments increased θ t and K sat and may also temporarily improve soil aggregation; however, SM amendments result in decreased K sat . Thus, it is not recommended that slurry SM be applied to the soils with low hydraulic conductivity because it could further inhibit water infiltration and increase surface runoff and soil erosion.

SOIL CARBON DYNAMICS DURING A LONG-TERM INCUBATION STUDY INVOLVING 13C AND 14C MEASUREMENTS

Soil organic matter is the earth's largest terrestrial reservoir of carbon (C). Thus, it serves as a major control on atmospheric carbon dioxide (CO2) levels. To better understand these controls, decreases in soil organic C (SOC), soil microbial biomass (SMB) C, and the role of SMB as a source of mineralizable C were measured during a long-term incubation (853 days) without added substrate. The 2 soils used were a Weld loam (fine montmorillonitic, mesic, Aridic Paleustoll) from near Akron, Colorado, and a Duroc loam (fine silty, mixed mesic Pachic Haplustoll) from near Sidney, Nebraska. The Akron soil was uniformly cropped to small grain crop-fallow rotations until 1989 when wheat (Triticum aestivum L.) in conventional (stubble mulch) till-fallow, reduced till-fallow, and no-till fallow treatments were adopted. On additional rotation plots, continuous corn (Zea mays L.) or no-till corn, fallow, wheat, and no-till corn in a 4-year rotation were grown. The Sidney soil was broken from native sod in 1970 and planted to wheat-fallow with no-till, plow-tillage, and sod-plot treatments. Moist soil samples were collected and refrigerated until plant material removal by sieving and picking. The SOC and SMB-C decreased during incubation and rates of loss measured. The results from this study allow insights into contributions of SMB and changes in soil isotope C ratios not previously available. Soil microbial biomass C contributed an average of 31% of the evolved CO2-C across all treatments between day 10 and day 79 of incubation and an average of about 20% during the more extended times between later measurements thereafter. Until day 160, evolution of 13CO2 during incubation indicated that evolved C came from plant residues and was soil derived thereafter, including from the native grassland SOC. Where corn was grown, evolution of evolved C is hypothesized to have had a less negative 13CO2 isotope signature from days 630 to 720 of the incubation because of the delayed microbial breakdown of the cob materials. After 853 days of incubation and across all plots, the SOC remaining averaged 67% and was similar to the amount of observed hydrolysis residue C. Acid hydrolysis and 14C dating were also used to characterize the resistant SOC fraction and showed increased 14C age with hydrolysis but not with long-term incubation.

Comparison of Fixed‐Wall and Pressurized‐Wall Minirhizotrons for Fine Root Growth Measurements in Eight Crop Species

Study of root growth is important for understanding C flow through plants to the soil and for modeling plant–soil interactions. Fine root growth can be observed through minirhizotrons (MRs), tubes installed in the field. We compared the use of fixed‐wall (F‐wall) MRs, 5.6 cm in diam., and pressurized‐wall (P‐wall) MRs, 9.6 cm in diam., with an inner cylinder and an outer wall of plastic sheeting kept under constant air pressure. Root growth was measured with a micro‐video camera for 3 yr in eight crop species growing on Pachic Haplustoll soil: canola, Brassica rapa L.; crambe, Crambe abysinnica Hochst. ex R.E. Fries; dry bean, Phaseolus vulgaris L.; dry pea, Pisum sativum L.; safflower, Carthamus tinctoris L.; spring wheat, Triticum aestivum L.; soybean, Glycine max (L.) Merr.; and sunflower, Helianthus anuus L. Midpoint depths of root length density profiles measured with P‐wall MRs were on average 20% greater than those from F‐wall MRs, and maximum rooting depths observed were 15% greater with P‐wall than with F‐wall MRs. Fixed‐wall MRs were forced into tight access holes to establish soil contact while the expectedly more uniform interfaces of P‐wall MRs apparently allowed more root penetration. Averages of total root lengths (TRL) over rootzones and of root length per MR area (for upper halves of rootzones) measured by F‐wall MRs were 47 and 32% greater, respectively, than those measured by P‐wall MRs. This is attributed to greater clarity and visibility in F‐wall MRs compared with P‐wall MRs. Significantly more effort is required to build and maintain P‐wall MRs compared with F‐wall MRs, but P‐wall MRs could be considered for use in problem soils with swelling clay content, stoniness, or gravel. In soils with fine‐textured, difficult subsoils, use of P‐wall MRs to supplement F‐wall MRs could increase the accuracy of root growth depth measures.

Management effects on soil CO 2 efflux in northern semiarid grassland and cropland

Soil respiration is a process influenced by land use, management practices, and environmental conditions. Our objectives were to evaluate relationships between management-induced differences in soil organic carbon (SOC) and soil CO 2 efflux from continuous no-till spring wheat ( Triticum aestivum L.), spring wheat-fallow under no-till, and a native mixed-grass prairie with grazing near Mandan, ND. A Werner–Sen–Chama soil complex (Entic Haplustoll, Typic Haplustoll, and Typic Calciustoll) was present at the grassland site and a Wilton silt loam (Pachic Haplustoll) at the cropping sites. Soil chambers were used to measure soil CO 2 effluxes about every 21 days starting 14 May 2001 to 1 April 2003. Soil water and soil temperature were measured at time of CO 2 efflux measurements. Soil organic carbon, microbial biomass carbon (MBC), and above and belowground plant biomass were measured in mid-July each year. Root biomass to 0.3 m depth of the undisturbed grassland was significantly greater (12.3 Mg ha −1) than under continuous wheat (1.3 Mg ha −1) and wheat-fallow (0.3 Mg ha −1). Grassland SOC content of 84 Mg ha −1 to 0.3 m soil depth was 1.2 times greater than continuous wheat and 1.3 times greater than wheat-fallow. The MBC of the grassland was 2.2 Mg ha −1, or 3.6 times greater than continuous wheat and 7.2 times greater than wheat-fallow treatments. Soil CO 2 efflux averaged 2.8 g CO 2–C m −2 day −1 for grassland, compared to 1.9 g CO 2–C m −2 day −1 for wheat fallow and 1.6 g CO 2–C m −2 day −1 for continuous wheat treatments. Although these CO 2 efflux rates were based on measurements made at intervals of about 21 days, the differences among treatments with time were rather consistent. Differences in soil CO 2 efflux among treatments could be attributed to differences in SOC and MBC, suggesting that land use plays a significant role in soil CO 2 efflux from respiration.

MANURE SOURCE EFFECTS ON SOIL PHOSPHORUS FRACTIONS AND THEIR DISTRIBUTION

Manure can be applied to soils as a major source of nutrients such as phosphorus (P). The environmental chemistry and plant availability of applied soil P are influenced by the chemical forms of P in the solid phase. The objectives of this study were to determine the amounts, availability, and chemical forms of P in a Hord silt loam soil (fine-silty, mixed, mesic Pachic Haplustoll) amended with beef and sheep feedlot, turkey house, and composted paunch manures. Manures were applied in alternate years from 1991 to 1997. In 1996, after three manure applications, total P in the manured 0-15-cm soil depth increased up to 14% and inorganic P up to 25% compared with nonmanured. Bray and Kurtz 1-P in 0-15-cm soil depth was almost 4 times greater in manured soil than in nonmanured (47.2 mg P kg -1 soil versus 12.7 mg P kg -1 soil). Soluble P was more than 4 times higher in the 0-15-cm depth of manured soils (13.9 mg P kg -1 soil) compared with nonmanured soil (3.2 mg P kg -1 soil). Nonoccluded P was more than 1.5 times higher in manure-amended soils (78.4 mg P kg -1 soil) than in nonmanured (46.8 mg P kg -1 soil) in the 0-15-cm soil depth. Occluded P in 0-15-cm soil depth was greatest in turkey manure-amended soil (45.2 mg P kg -1 soil), followed by beef manure-amended soil (36.7 mg P kg -1 soil). In 1997, all P fractions were higher in 0-7.5-cm depth than any other amended soil depth, and the same general trends among fractions held as in 1996. Although animal source of applied manure does have some influence on P fractionation and depth distribution, most P remains in the zone of application, emphasizing the need for conservation of the surface soil.

EFFECT OF SWINE LAGOON WATER APPLICATION RATE AND ALFALFA HARVEST FREQUENCY ON DRY MATTER PRODUCTION AND N HARVEST

Swine (Sus scrofa domesticus) lagoon water can supply valuable fertilizer nutrients for field crops. Reduced landavailability and increased swine operation size can potentially create situations where swine producers may over-applylagoon water and contaminate groundwater. This study was initiated in fall 1992 at the Haskell Agricultural Laboratory nearConcord, Nebraska, on a Blendon sandy loam (coarse-loamy, mixed, Pachic Haplustoll). The objectives were to determinehow harvesting alfalfa three times per year (3-HF), four times per year (4-HF), or five times per year (5-HF) and swinelagoon water application rate affected dry matter production and nitrogen (N) harvest by alfalfa (Medicago sativa L.). Swinelagoon water from an anaerobic lagoon was applied to alfalfa using a line-source sprinkler system at rates of 14, 109, 239,394, 509, and 634 kg N ha-1 in 1993 and 14, 114, 249, 399, 519, and 644 kg N ha-1 in 1994. In 1993, alfalfa dry matterproduction increased linearly with increasing lagoon water application rate. In 1994, lagoon water application of 644 kg Nha-1 significantly increased dry matter production by 1.9 Mg ha-1. Dry matter production averaged 19.2, 22.5, and 21.5 Mgha-1, for the 3-HF, 4-HF, and 5-HF treatments, respectively. Nitrogen harvest increased linearly with lagoon waterapplication rate in 1993 and 1994.

Comparison of S1 with Open‐Pollination Progenies in Selection for Yield in Crested Wheatgrass

Genetic gain from selection for high dry matter yield in most cross‐pollinated forage grasses has been an elusive goal, in spite of sustained breeding efforts. This study was conducted to determine the value of one generation of self‐pollinating (S1) before selection for yield in crested wheatgrass (Agropyron spp.). Dry matter yields were compared at two locations near Mandan, ND, for synthetic populations derived from selection among and within S1 or among and within open‐pollination (OP) progenies from three source populations. Within each source population, the 20 parents used to produce S1 progenies were in common with the 20 maternal parents of the OP progenies. Soil was a Parshall fine sandy loam (coarse‐loamy, mixed, superactive, frigid Pachic Haplustolls) at Location 1 and a Wilton silt loam (fine‐silty, mixed, superactive, frigid Pachic Haplustolls) at Location 2. In space‐plant tests, S1 family means for dry matter yield averaged 52% of OP family means, indicating high levels of inbreeding depression. In solid‐seeded tests, yield differences between S1– and OP‐derived synthetic populations were significant (P ≤ 0.05) for only one comparison. On the basis of three distinct source populations, we found that S1 and OP families were both effective when used as the selection unit to choose high yielding parents for synthetic populations. Additional resources required to produce and evaluate S1 families over OP families could not be justified in the crested wheatgrass source populations evaluated in this study.

Tillage and cropping effects on soil quality indicators in the northern Great Plains

The extreme climate of the northern Great Plains of North America requires cropping systems to possess a resilient soil resource in order to be sustainable. This paper summarizes the interactive effects of tillage, crop sequence, and cropping intensity on soil quality indicators for two long-term cropping system experiments in the northern Great Plains. The experiments, located in central North Dakota, were established in 1984 and 1993 on a Wilton silt loam (FAO: Calcic Siltic Chernozem; USDA 1 The US Department of Agriculture, Agricultural Research Service is an equal opportunity/affirmative action employer and all agency services are available without discrimination. 1 : fine-silty, mixed, superactive frigid Pachic Haplustoll). Soil physical, chemical, and biological properties considered as indicators of soil quality were evaluated in spring 2001 in both experiments at depths of 0–7.5, 7.5–15, and 15–30 cm. Management effects on soil properties were largely limited to the surface 7.5 cm in both experiments. For the experiment established in 1984, differences in soil condition between a continuous crop, no-till system and a crop–fallow, conventional tillage system were substantial. Within the surface 7.5 cm, the continuous crop, no-till system possessed significantly more soil organic C (by 7.28 Mg ha −1), particulate organic matter C (POM-C) (by 4.98 Mg ha −1), potentially mineralizable N (PMN) (by 32.4 kg ha −1), and microbial biomass C (by 586 kg ha −1), as well as greater aggregate stability (by 33.4%) and faster infiltration rates (by 55.6 cm h −1) relative to the crop–fallow, conventional tillage system. Thus, soil from the continuous crop, no-till system was improved with respect to its ability to provide a source for plant nutrients, withstand erosion, and facilitate water transfer. Soil properties were affected less by management practices in the experiment established in 1993, although organic matter related properties tended to be greater under continuous cropping or minimum tillage than crop sequences with fallow or no-till. In particular, PMN and microbial biomass C were greatest in continuous spring wheat (with residue removed) (22.5 kg ha −1 for PMN; 792 kg ha −1 for microbial biomass C) as compared with sequences with fallow (SW–S–F and SW–F) (Average=15.9 kg ha −1 for PMN; 577 kg ha −1 for microbial biomass C). Results from both experiments confirm that farmers in the northern Great Plains of North America can improve soil quality and agricultural sustainability by adopting production systems that employ intensive cropping practices with reduced tillage management.

Russian Wildrye Seedling Development under Three Temperature Regimes

Poor seedling vigor of Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] has resulted in frequent establishment failures and deterred more widespread use of this grass. This study was conducted to ascertain coleoptile length and seedling emergence of Russian wildrye under three temperature regimes at a 70-mm planting depth in a Parshall fine-sandy loam soil (coarse-loamy, mixed, superactive, frigid Pachic Haplustolls; bulk density = 1.3 g cm−3) and to compare seedling development of four tetraploid populations with two diploid check cultivars. Diurnal temperatures (12/12 h, both dark) were 7/10°C (low), 13/16°C (medium), and 19/22°C (high). Soil water was maintained near field capacity. Coleoptile lengths for the low-, medium-, and high-temperature treatments averaged 48.3, 50.2, and 55.5 mm, respectively. Low and sporadic seedling emergence of ‘Vinall’ at all temperature treatments resulted in a significant (P ≤ 0.01) entry × temperature interaction. Entries had similar ranking for emergence within each temperature regime, and all entries but Vinall had increased emergence in response to increasing temperatures. Seedling emergence from a 70-mm planting depth was dependent on elongation of both the coleoptile and first seedling leaf, and diploid entries failed to emerge in most instances. Seedling emergence at the low-, medium-, and high-temperature treatments averaged 4.5, 14.5, and 16.5%, respectively, for the two diploid check cultivars and 16.5, 27.0, and 37.0%, respectively, for the four tetraploid populations. Tetraploids had greater seedling establishment potential than diploids, but any advantage for early-spring seeding would be due to factors other than soil temperature.

Root Length Growth of Eight Crop Species in Haplustoll Soils

Quantifying the dynamics of root growth is necessary for knowledge about development of rhizoplane and rhizosphere structure, and will indicate potentials for soil C sequestration and for water and nutrient usage. Root growth was measured during 3 yr in spring wheat (Triticum aestivum L.) on fallow and in seven crops in spring wheat–winter wheat–alternative crop rotation under minimum tillage on Wilton silt loam (fine silty, mixed, superactive, frigid Pachic Haplustolls). Two types of minirhizotrons (standard [Stand MR] and pressurized‐wall [P‐wall MR]) were read with a microvideo camera. Average maximum rooting depths fell into agronomic groups: oilseeds safflower (Carthamus tinctoris L.), 1.64 m, and sunflower (Helianthus annuus L.), 1.45 m; spring wheat, 1.31 m; mustard family crops crambe (Crambe abysinnica Hochst. ex R. E. Fr.), 1.17 m, and canola (Brassica rapa), 1.13 m; and legumes dry bean (Phaseolus vulgaris L.), 1.00 m, soybean [Glycine max (L.) Merr.], 0.99 m, and dry pea (Pisum sativum L.), 0.99 m. Median depths of root length growth ranged from 0.92 m for safflower to 0.46 m for dry bean, and ratios of median to maximum depths averaged 0.51. Six out of eight crops showed greatest rooting depths in relatively wet 1995, likely because of wetter subsoil. Greatest total root length in safflower, crambe, canola, soybean and dry bean occurred in drier‐than‐average 1997, which is interpreted as a response to soil water deficit. Results indicate that diverse crop rotations have the potential to utilize water and nutrients and input C over different soil profile positions than spring wheat‐based monocropping.

Root Length Growth of Eight Crop Species in Haplustoll Soils

Quantifying the dynamics of root growth is necessary for knowledge about development of rhizoplane and rhizosphere structure, and will indicate potentials for soil C sequestration and for water and nutrient usage. Root growth was measured during 3 yr in spring wheat (Triticum aestivum L.) on fallow and in seven crops in spring wheat–winter wheat–alternative crop rotation under minimum tillage on Wilton silt loam (fine silty, mixed, superactive, frigid Pachic Haplustolls). Two types of minirhizotrons (standard [Stand MR] and pressurized-wall [P-wall MR]) were read with a microvideo camera. Average maximum rooting depths fell into agronomic groups: oilseeds safflower (Carthamus tinctoris L.), 1.64 m, and sunflower (Helianthus annuus L.), 1.45 m; spring wheat, 1.31 m; mustard family crops crambe (Crambe abysinnica Hochst. ex R. E. Fr.), 1.17 m, and canola (Brassica rapa), 1.13 m; and legumes dry bean (Phaseolus vulgaris L.), 1.00 m, soybean [Glycine max (L.) Merr.], 0.99 m, and dry pea (Pisum sativum L.), 0.99 m. Median depths of root length growth ranged from 0.92 m for safflower to 0.46 m for dry bean, and ratios of median to maximum depths averaged 0.51. Six out of eight crops showed greatest rooting depths in relatively wet 1995, likely because of wetter subsoil. Greatest total root length in safflower, crambe, canola, soybean and dry bean occurred in drier-than-average 1997, which is interpreted as a response to soil water deficit. Results indicate that diverse crop rotations have the potential to utilize water and nutrients and input C over different soil profile positions than spring wheat-based monocropping.

Spatial Analysis of Machine‐Wheel Traffic Effects on Soil Physical Properties

Infiltration in irrigation furrows exhibits spatial variation from furrow to furrow within a field. One major contributing factor is the effect of multiple levels of machine‐wheel traffic on soil physical properties. The purpose of this study was to determine the effect of machine‐wheel traffic levels within equipment passes on a field basis. Variations in satiated hydraulic conductivity (Ks), penetrometer resistance (Rp), and bulk density (ρb) due to nine, eight‐row equipment passes were studied in three transects, crossing 72 furrows perpendicular to crop rows, on a Hord silt loam (fine‐silty, mixed, mesic, Pachic Haplustoll). Mean values, spatial patterns, and regression relationships between properties were determined. Spectral analysis was used to fit cosine curves to property data that showed significant periods at 2.7, 8.0, and 72 furrows. An additional period of 24 furrows was seen in the Rp and ρb data. All properties tested showed significant mean differences due to wheel traffic from equipment passes. Within the equipment passes it was possible to further separate treatment means for all soil properties. Results in wheel tracked furrows were different from all other treatments. Linear regression of log Ks and Rp in a 72‐furrow transect shows 58% of log Ks variability is explained by changes in Rp Predicted vs. measured log Ks in two transects shows predictions somewhat high, although the slope of the linear regression is 0.95, nearly parallel to a 1:1 line.

Dry Matter Yields of Cool‐Season Grass Monocultures and Grass–Alfalfa Binary Mixtures

Cultivars used in grass–alfalfa (Medicago sativa L.) mixtures for hay production in the semiarid Northern Great Plains have often lacked long‐term productivity. This study was conducted to compare dry matter (DM) yields of grass monocultures and grass–alfalfa binary mixtures receiving annual applications of 0 and 50 kg N ha−1 over a 5‐yr period. ‘Reliant’ and ‘Manska’ intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. and Dewey], ‘Lincoln’ smooth bromegrass (Bromus inermis Leyss.), ‘Nordan’ crested wheatgrass [Agropyron desertorum (Fisch.) Schult.], ‘Lodorm’ green needlegrass (Stipa viridula Trin.), and ‘Dacotah’ switchgrass (Panicum virgatum L.) were seeded in monoculture and in binary mixtures with ‘Rangelander’ alfalfa [Medicago sativa subsp. × varia (Martyn) Arcang.] on a Parshall fine sandy loam (coarse‐loamy, mixed, superactive, frigid, Pachic Haplustolls) near Mandan, ND. Plant stands of green needlegrass and switchgrass were inadequate, and yields were not measured. Total seasonal DM yields from two cuttings averaged 8.74 and 2.71 Mg ha−1, respectively, for grass–alfalfa mixtures and grass monocultures at 0 kg N ha−1. At 50 kg N ha−1, grass–alfalfa mixtures and grass monocultures averaged 8.72 and 5.04 Mg ha−1 DM yield, respectively. Yields of the grass component of first cut grass–alfalfa mixtures averaged 35% of total yield for intermediate wheatgrass, 33% of total yield for smooth bromegrass, and 30% of total yield for crested wheatgrass in the fifth production year. Cultivars included in this study, except those of green needlegrass and switchgrass, would be suited for use in binary grass–alfalfa mixtures for dryland hay production in the Northern Great Plains.

Comparison of Three Leaf Area Index Meters in a Corn Canopy

Measurement of leaf area index (LAI) is critical to understanding many aspects of crop development, growth, and management. Availability of portable meters to estimate LAI non‐destructively has greatly increased our ability to determine this parameter during the cropping season. However, with several devices on the market, each with an independent set of protocols for gathering accurate estimates of LAI, it is necessary for scientists to have comparisons of these meters under field conditions before selecting one for purchase and use. The objective of our study was to compare the LAI estimates by three meters (AccuPAR, LAI‐2000, and SunScan) to LAI measured by destructive sampling. Leaf area index of two corn (Zea mays L.) hybrids, grown on a Pachic Haplustoll, was measured at the R2 stage by the four methods before and after successive thinning of plant stands. Destructively sampled LAI ranged from 4.59 to 1.25 for the initial stand to the most severe thinning. Hybrids did not differ in LAI. All meters underestimated LAI compared with destructive sampling. When all data from all rings of the LAI‐2000 meter were included in the calculations, LAI‐2000 estimates of LAI differed from those of the other two meters. However, when data from Ring 5 was removed from the calculations, estimates of LAI for the LAI‐2000 improved and were indistinguishable from the other meters. The relationship between LAI estimated destructively and by each of the meters was described by a unique linear equation for each hybrid. Results of this study, and experience with use of the meters, suggest that users should consider protocols for operating each meter before deciding which device best suits their application.

Soil Water Use by Diploid and Tetraploid Russian Wildrye

Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] is an important cool‐season forage grass for the Northern Great Plains, but it exhibits poor seedling vigor. Tetraploid (2n=4x=28) plants have improved seedling vigor over diploid (2n=2x=14) plants, but data is lacking on plant‐soil‐water relations. Objectives of this research were to compare water‐use efficiency (WUE), evapotranspiration (ET), roofing activity, and water extraction in relation to Haun stage for diploid and tetraploid Russian wildrye. A diploid and tetraploid entry were evaluated for 3 yr under two water treatments (50 and 150% of monthly average precipitation for 1 April to 1 November) and two fertilizer rates (10 and 134 kg N ha−1) in a rain shelter. The soil was a Parshall fine sandy loam (Coarse‐loamy, mixed, superactive, frigid Pachic Haplustoll). Cumulative ET averaged across the 50 and 150% water treatments was 138 and 141 mm for the diploid and tetraploid, respectively. Rate of root activity progression was linear with Haun to the 1.2‐m depth and ranged from 0.148 to 0.163 m per Haun stage for the diploid and tetraploid, respectively, at 50% water. Forage yield of the tetraploid was greater than the diploid at the 50%, but not at the 150% water treatment. Water‐use efficiency was higher for the tetraploid (3.8 g kg−1) than the diploid (3.1 g kg−1) at the 50% water treatment, but at 150% water the entries were not different. Overall, the tetraploid entry exhibited a more favorable WUE and other soil water relations than did the diploid entry.

Microbial contributions to the aggregation of a cultivated grassland soil amended with starch

The activity of microorganisms, especially fungi, is thought to play a key role in the formation and stabilization of macroaggregates in many soils. Our aim was to follow the aggregate formation and stabilization of organic matter in a controlled laboratory experiment, where microaggregates (53–250 μm) obtained by slaking of a cultivated Duroc loam (fine–silty, mixed, mesic Pachic Haplustoll) were incubated with 13C-labelled granular starch equivalent to 8 mg starch-C g −1 soil. Over 71 d we measured the size distribution of water-stable aggregates, followed the dynamics of native and labelled C within the aggregate-size classes, and estimated the development of the microbial biomass by chloroform fumigation–extraction and by direct counting. After an initial flush of starch decomposition, at d 4 macroaggregates (250–8000 μm) represented 56% of the soil mass and contained 6.3 mg starch-derived C g −1 soil compared with 1.6 mg starch-derived C g −1 soil in the 53–250-μm microaggregates. The concentration of starch-derived C isolated in microbial biomass at d 4 was 3270 μg g −1 soil in the macroaggregates and 630 μg g −1 soil in the microaggregates and declined thereafter in both size classes. At d 4, fungal biomass predominated the microbial community in the macroaggregates, in all other samples bacterial biomass predominated. The mass of soil found in macroaggregates did not follow the decline in fungal and bacterial biomass with incubation-time but remained constant. Except at the last sampling date, we observed no formation of macroaggregates in the control samples (incubated without starch amendment), and the undecomposed starch did not glue microaggregates into macroaggregates either. We suggest that microhabitats enriched in substrate acted as `hot spots' for fungal growth towards and on these sources. In accordance with previous studies, the resulting filamentous entanglement of primary particles and microaggregates formed macroaggregates. However, the stabilization of the macroaggregates throughout the experiment may be attributed to other factors that persist after cell death of the microorganisms. In situ mineralization rate constants of labelled C were much lower for the microaggregates, compared with those of the macroaggregates, indicating a better stabilization of starch-derived C within the microaggregates, and thus supporting the macroaggregate–microaggregate conceptual model.