Little is known about the long-term tillage and cropping management effects on the microbiologically derived factors that influence macroaggregates in semi-arid soil. We tested the hypothesis that differences in macro-aggregation are due to changes in soil structure related to management treatment-induced microbiological changes. In an experiment, microbiological factors consisting of aggregate stability, glomalin, russuloid basidiomycete fungi, uronic acids, total organic C (TOC), and total N (TN) were quantified in macroaggregate-size classes ranging from 4.75 to 0.25 mm, collected at 0–5 cm depth for the following treatments: (1) 12th year of fallow phase after 11 years of conventional- and no-tilled spring wheat-fallow (CTF and NTF), (2) 12th year of lentil phase after 11 years of conventional- and no-tilled spring wheat-lentil (CTL and NTL), (3) 12 years no-tilled continuous spring wheat (NTCW), and (4) 16 years uncultivated pasture (P) used as a baseline treatment. Immunoreactive easily extractable glomalin concentration was five to six times greater under P, NTCW, or NTL in the 2.00–1.00- and 1.00–0.50-mm macroaggregate-size classes than the other treatments and these results corroborated well with the results from aggregate stability assays. Russuloid basidiomycetes were highest in all NTCW macroaggregate-size classes, suggesting that annual input of lignin-containing wheat residues may influence the growth and survival of these fungi. Uronic acid amounts were highest in P but did not differ among the other treatments. In all macroaggregate-size classes, TOC content was greater in NTCW compared to CTF, and TN was about three times higher in NTL than NTF or CTF. In conclusion, 12 years of NTCW management in semi-arid soil has resulted in higher macroaggregate stability, glomalin concentration, russuloid basidiomycete populations, and TOC in macroaggregates compared to alternate-year fallow. Lentil can be used to replace fallow in dryland wheat rotation under no-till to enhance TN content and improve soil macro-aggregation.

Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. The 21-yr effects of the combinations of tillage and cropping sequences was evaluated on dryland crop grain and biomass (stems+leaves) N, soil surface residue N, soil N fractions, and N balance at the 0–20cm depth in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat–barley (Hordeum vulgare L.) (1984–1999) followed by spring wheat–pea (Pisum sativum L.) (2000–2004) (FSTW-B/P), and spring-tilled spring wheat–fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4-N, and NO3-N. Annualized crop grain and biomass N varied with treatments and years and mean grain and biomass N from 1984 to 2004 were 14.3–21.2kgNha−1 greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue N was 9.1–15.2kgNha−1 greater in other treatments than in STW-F in 2004. The STN at 0–20cm was 0.39–0.96MgNha−1, PON 0.10–0.30MgNha−1, and PNM 4.6–9.4kgNha−1 greater in other treatments than in STW-F. At 0–5cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5–20cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO3-N was greater in FSTW-B/P than in NTCW and FSTCW. Estimated N loss through leaching, volatilization, or denitrification at 0–20cm depth increased with increasing tillage frequency or greater with fallow than with continuous cropping and ranged from 9kgNha−1yr−1 in NTCW to 46kgNha−1yr−1 in STW-F. Long-term no-till or spring till with continuous cropping increased dryland crop grain and biomass N, soil surface residue N, N storage, and potential N mineralization, and reduced N loss compared with the conventional system, such as STW-F, at the surface 20cm layer. Greater tillage frequency, followed by pea inclusion in the last 5 out of 21yr in FSTW-B/P, however, increased N availability at the subsurface layer in 2004.

Long-term management practices are needed to increase dryland C storage and improve soil quality. We evaluated the 21-yr effects of combinations of tillage and cropping sequences on dryland crop biomass (stems + leaves) returned to the soil, residue C, and soil C fractions at the 0- to 20-cm depth in a Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiborolls) in eastern Montana. Treatments were no-till continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat-barley (Hordeum vulgare L.) (1984-1999) followed by spring wheat-pea (Pisum sativum L.) (2000-2004) (FSTW-B/P), and spring-tilled spring wheat-fallow (STW-F). Carbon fractions were soil organic C (SOC), soil inorganic C (SIC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Mean crop biomass was 53 to 66% greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue amount and C content in 2004 were 46 to 60% greater in NTCW and FSTCW than in STW-F As a result, soil C fractions at 0 to 20 cm were 23 to 141 % greater in all other treatments than in STW-F due to increased C input. At 0 to 5 cm, SOC, SIC, POC, and PCM were greater in NTCW than in FSTW-B/P. At 5 to 20 cm, POC was greater in NTCW than in FSTW-B/P and PCM was greater in STCW than in FSTCW. Long-term reduced tillage with continuous nonlegume cropping increased dryland crop biomass, residue and soil C storage, and soil quality by increasing microbial biomass and activities compared with a conventional system such as STW-F.

Plot-scale field studies were conducted to evaluate the efficacy of steam for the control of cropland weeds in comparison with common herbicides. Weed densities, biomass, or emergence after treatment were measured. Steam (3,200 kg/ha, energy dosage equivalent to 890 kJ/m2, speed of 0.8 m/s) and glyphosate (560 g ai/ha) gave similar control (> 90%) of seedling common lambsquarters and seedling redroot pigweed. Applied at heading, steam was comparable to glyphosate in reducing green foxtail biomass at heading 2 wk after application. Steam applied at a rate of 3,200 kg/ha significantly reduced weed biomass (mixed stand, treated at seedling stage) 9 wk after application compared with the control, whereas steam applied at a rate of 1,600 kg/ha (1.6 m/s) did not. Biomass of downy brome treated with steam was reduced more at anthesis than at the seedling growth stage. Emergence of common lambsquarters, redroot pigweed, and black nightshade was not affected by steam application. Amount of steam applied, weed species, and growth stage are key factors in determining control effectiveness. Nomenclature: Glyphosate; black nightshade, Solanum nigrum L. #3 SOLNI; downy brome, Bromus tectorum L. # BROTE; common lambsquarters, Chenopodium album L. # CHEAL; green foxtail, Setaria viridis L. # SETVI; redroot pigweed, Amaranthus retroflexus L. # AMARE. Additional index words: Kochia scoparia L. Schrad., KOCSC, paraquat, pelargonic acid, SALIB, Salsola iberica Sennen & Pau.

Soil organic C (SOC) analyses using high temperature induction furnace combustion methods have become increasing popular because of advances in instrumentation. Combustion methods, however, also include C from CaCO 3 and CaMg(CO 3 ) 2 found in calcareous soils. Separate analysis of the inorganic C (IC) must be done to correct C data from combustion methods. Our objective was to develop a efficient and precise IC method by modification of the pressure‐calcimeter method. We modified the method by using Wheaton serum bottles (20‐mL and 100‐mL) sealed with butyl rubber stoppers and aluminum tear‐off seals as the reaction vessel and a pressure transducer monitored by a digital voltmeter. Our gravimetric IC determination of six soils showed a strong correlation when regressed against IC from the modified pressure‐calcimeter method (slope of 0.99, r 2 = 0.998). The method detection limit (MDL) was 0.17 g IC kg −1 for the 20‐mL serum bottles and the limit of quantification (LOQ) was 0.30 g IC kg −1 The 100‐mL serum bottle had a MDL of 0.42 with a LOQ of 2.4 g IC kg −1 When using a 100‐mL Wheaton serum bottle as the reaction vessel with a 0.50‐g sample size, soils containing up to 120 g IC kg −1 , which represent a 100 % CaCO 3 equivalent, can be analyzed within the V output range of the pressure transducer. Soil organic C determined by subtraction of IC from total C from combustion analysis correlated well with SOC determined by the Walkley‐Black.

Plot-scale field studies were conducted to evaluate the efficacy of steam for the control of cropland weeds in comparison with common herbicides. Weed densities, biomass, or emergence after treatment were measured. Steam (3,200 kg/ha, energy dosage equivalent to 890 kJ/m(2), speed of 0.8 m/s) and glyphosate (560 g ai/ha) gave similar control (> 90%) of seedling common lambsquarters and seedling redroot pigweed. Applied at heading, steam was comparable to glyphosate in reducing green foxtail biomass at heading 2 wk after application. Steam applied at a rate of 3,200 kg/ha significantly reduced weed biomass (mixed stand, treated at seedling stage) 9 wk after application compared with the control, whereas steam applied at a rate of 1,600 kg/ha (1.6 m/s) did not. Biomass of downy brome treated with steam was reduced more at anthesis than at the seedling growth stage. Emergence of common lambsquarters, redroot pigweed, and black nightshade was not affected by steam application. Amount of steam applied, weed species, and growth stage are key factors in determining control effectiveness.

Cycling of N through an agroecosystem can be managed more effectively if effects of N management and cropping sequence on soil N microbial processes are understood. Effects of cropping intensity and N fertilizer rate on net soil N mineralization were studied as well as their correlation with precipitation, air temperature and soil water content. Net soil N mineralization was measured by incubating undisturbed soil cores (15-cm depth) containing anion and cation exchange resins at their bottoms, Cores were incubated during each of five time periods (3-4 wk each) during the fallow phase (mid-April to mid-September) of two no-till cropping systems, wheat (Triticum aestivum L,)-fallow (WF) and wheat-corn (Zea mays L.)- fellow (WCF). Past N fertilizer applications were over four rates with total amounts applied during the previous 6 yr of 0, 95, 190, and 286 kg N ha(-1) in WF and 0, 134, 269, and 403 kg N ha(-1) in WCF, Soils were an Aridic Paleustoll at Sterling and an Aridic Argiustoll at Stratton in eastern Colorado, Total net N mineralization in WCF was half that in WP (22 vs. 43 kg N ha(-1); 2-site average), probably due to greater immobilization as evidenced by nearly three times greater accumulation of crop residue on the soil surface after 6 Sr of no-till management. Greater conservation of applied N and soil N can be expected in the more intensive WCF system, Total mineralized N increased with N rate by approximate to 0.2 kg ha(-1) for each kg ha(-1) of previously applied N, Precipitation in combination with air temperature and their interaction term gave the best prediction of average daily N mineralization at both sites.

Direct quantitative measurement of soil net N mineralization in agricultural soils under field conditions has not been widely used. A potential method of in situ net N mineralization was investigated in the fallow phase of a 3-yr no-till crop rotation at two sites. Undisturbed soil cores (5 by 15 cm) with anion- and cation-exchange resins (Sybron Ionac ASB-1P and C-249) at the bottom were incubated in situ. Nitrate-N plus NH4+-N extracted from soil was added to extracted amounts from resin bags to determine net N mineralized during each of three incubation periods (3-4 wk each). Total net N mineralization was 33.7 and 26.5 kg N ha(-1) during 84 and 75 d of incubation at Sterling and Stratton, respectively. Relative amounts of resin did not affect N captured but cores placed midway between old corn (Zea Mays L.) rows tended to accumulate more (P > F = 0.13) N than cores placed in rows. This in situ method appears to be a reliable method for measuring net N mineralization in the field; however, variation is large and many observations are required to obtain net N mineralization rates within an acceptable confidence interval.

Crop N needs are not usually predicted based on cropping intensity or on tillage practice. However, N fertilizer requirements may increase dramatically as less fallow and less tillage are used in semi-arid regions of the Great Plains where summer fallow cropping is common. This long-term experiment was conducted to study the influence of N fertilizer rate, source/placement/timing (NSP), and crop rotation factors on the production of winter wheat (Triticum aestivum L.), corn (Zea mays L.), and grain sorghum (Sorghum bicolor L.), as well as their fertilizer N use efficiency (FNUE) for the initial years of conversion to no-till dryland farming. Research was conducted from 1987 through 1992 on two soils (Keith clay loam, a fine-silty, mixed, mesic Aridic Argiustoll and Weld loam, a fine-silty, mixed, mesic, Aridic Argiustoll) in eastern Colorado. Rotations included winter wheat-fallow (WF) and winter wheat-corn or grain sorghum-fallow (WCF). Wheat yields were similar between WF and WCF with adequate N application. Response to N fertilizer at lower rates was greater in WCF than WF because of its greater depletion of soil N. Corn production averaged 72 bu/acre with adequate N and required 1 Ib/acre of N uptake to produce 1 bu/acre of grain. Current N fertilizer recommendations for wheat and corn were not adequate to insure maximum production under no-till management. Fertilizer placement significantly affected average annual rotational yield (40 to 70 Ib/acre per yr difference) but application rate was more important economically. Grain biomass produced in each rotation per pound of total plant N uptake (GNUE) was 17 Ib/acre per yr in WF compared with 29 Ib/acre per yr for WCF. This 70% increase in average annual grain production of WCF over WF was accomplished with a 44% annual increase in fertilizer N application.