• Authors:
    • Ahuja, L. R.
    • Westfall, D. G.
    • Peterson, G. A.
    • Sherrod, L. A.
  • Source: Soil Science Society of America Journal
  • Volume: 69
  • Issue: 5
  • Year: 2005
  • Summary: Previous studies of no-till management in the Great Plains have shown that increased cropping intensity increased soil organic carbon (SOC). The objectives of this study were to (i) determine which soil C pools (active, slow, and passive) were impacted by cropping intensity after 12 yr of no-till across potential evapotranspiration (PET) and slope position gradients; (ii) relate C pool sizes to the levels found in total SOC; and (iii) determine C pool sizes relative to C levels found in a grass treatment (G). Cropping systems were wheat (Triticum aestivum)-fallow (WIT), wheat-corn (Zea mays L.)-fallow (WCF), wheat-corn-millet (Panicum miliaceum)-fallow (WCMF), and continuous cropping (CC) at three PET sites in Colorado. Active C (Soil microbial biomass C [SMBC]); and slow pool C (particulate organic matter C; POM-C) increased as cropping intensity increased, dependent on PET. Passive C (mineral associated organic C [MAOC]) was strongly influenced by a site-by-slope position interaction but not by cropping system. Toeslope soils had 35% higher POM-C compared with summits and sideslopes. All C pools were strongly correlated with total SOC, with the variability decreasing as C pool turnover time increased. Carbon pool sizes in cropping systems relative to levels found in G were independently influenced by cropping system. The highest were found in the CC system, which had 91, 78, and 90% of the amounts of C found in the perennial G system in the active, slow, and passive C pools, respectively.
  • Authors:
    • Robertson, G. P.
    • McSwiney, C. P.
  • Source: Global Change Biology
  • Volume: 11
  • Issue: 10
  • Year: 2005
  • Summary: The relationship between nitrous oxide (N2O) flux and N availability in agricultural ecosystems is usually assumed to be linear, with the same proportion of nitrogen lost as N2O regardless of input level. We conducted a 3-year, high-resolution N fertilizer response study in southwest Michigan USA to test the hypothesis that N2O fluxes increase mainly in response to N additions that exceed crop N needs. We added urea ammonium nitrate or granular urea at nine levels (0-292 kg N ha-1) to four replicate plots of continuous maize. We measured N2O fluxes and available soil N biweekly following fertilization and grain yields at the end of the growing season. From 2001 to 2003 N2O fluxes were moderately low (ca. 20 g N2O-N ha-1 day-1) at levels of N addition to 101 kg N ha-1, where grain yields were maximized, after which fluxes more than doubled (to >50 g N2O-N ha-1 day-1). This threshold N2O response to N fertilization suggests that agricultural N2O fluxes could be reduced with no or little yield penalty by reducing N fertilizer inputs to levels that just satisfy crop needs.
  • Authors:
    • Arshad, M.
    • Klein-Gebbinck, H.
    • Soon, Y.
  • Source: Canadian Journal of Plant Science
  • Volume: 85
  • Issue: 1
  • Year: 2005
  • Summary: Brown girdling root rot (BGRR) is a serious and widespread disease of canola ( Brassica rapa L.) in the Peace River region of northwestern Canada. There is no chemical control treatment for the pathogen, and farmers have observed that the disease is more severe when canola follows red fescue ( Festuca rubra L.) or clover ( Trifolium spp.) compared to summer fallow. A field study was conducted to determine how crop sequences following red fescue termination can be combined with residue and tillage management to reduce BGRR infection and increase canola yield. The five treatments consisted of rotations of: continuous canola (CCC) and oat ( Avena sativa L.)-oat-canola (OOC), both managed using reduced tillage (RT), and wheat ( Triticum aestivum L.)-wheat-canola (WWC), managed using RT, conventional tillage (CT) or no-till (NT). Canola yield followed the trend: OOC(RT)=WWC(RT) > WWC(CT) > CCC(RT)=WWC(NT). BGRR infection increased with tillage intensity: WWC(CT) > CCC(RT)=WWC(RT)=OOC(RT) > WWC(NT), and was reduced when canola followed two cereal break crops. Yield was highest when canola was preceded by a cereal crop and lowest without a break crop. The low yield with NT was attributed to poor crop emergence from a hard seed bed with unbroken turf and to competition from re-emerged fescue in the third year after fescue breaking. This study demonstrated that the cropping sequence and tillage system used influenced canola yield to a greater extent than did BGRR infection.
  • Authors:
    • Álvaro-Fuentes, J.
    • Arrúe, J. L.
    • López, M. V.
    • Moret, D.
  • Source: European Journal of Agronomy
  • Volume: 23
  • Issue: 1
  • Year: 2005
  • Summary: Most of the benefits from conservation tillage are attained by maintaining crop residues on the soil surface. However, the effectiveness of crop residues depends on their persistence in time and maintenance of sufficient residue cover can become difficult, especially when a long-fallow period is involved. In this study, we evaluate the effects of conventional tillage (CT) and two conservation tillage systems (reduced tillage, RT, and no-tillage, NT), under both continuous cropping (CC) and cereal-fallow rotation (CF), on the dynamics of surface barley residues during four fallow periods in a dryland field of semiarid Aragon. The CC system involves a summer fallow period of 5-6 months and the CF rotation a long-fallow of 17-18 months. Results indicate that the lack of residue-disturbing operations in NT makes this practice the best strategy for fallow management. With this tillage system, the soil surface still conserved a residue cover of 10-15% after long-fallowing and percentages of standing residues ranging from 20 to 40% of the total mass after the first 11-12 months. In both CT and RT, primary tillage operations had the major influence on residue incorporation, with percentages of cover reduction of 90-100% after mouldboard ploughing (CT) and 50-70% after chiselling (RT). Two decomposition models were tested, the Douglas-Rickman and the Steiner models. Our data indicate that the Steiner model described more accurately the decline of surface residue mass over the long-fallow period in the NT plots. Measured and predicted data indicate that, under NT, 80-90% of the initial residue mass is lost at the end of fallow and that 60-75% of this loss occurs during the first 9-10 months. Finally, the mass-to-cover relationship established in this study for barley residues could be used to predict soil cover from flat residue mass through the fallow period by using a single A(m) coefficient (0.00208 ha kg(-1)). (C) 2004 Elsevier B.V. All rights reserved.
  • Authors:
    • Price, A.
    • Saini, M.
    • van Santen, E.
  • Source: 2005 Southern Conservation Tillage Systems Conference, Oral Proceedings, Clemson University
  • Year: 2005
  • Summary: An integral component of a conservation-tillage system in corn (Zea mays L.) and cotton (Gossypium hirsutum L.) is the use of a winter cover crop. A field experiment was initiated in 2002 to evaluate winter weed dynamics following various winter cover crops in both continuous cotton and a corn and cotton rotation. Winter cover crops included black oats (Avena strigosa Schreb.); two crimson clover entries (Trifolium incarnatum L.); two cultivars of forage rape (Brassica napus L. var. napus), spring and winter; oil radish (Raphanus sativus var. oleiformis Pers.); three cultivars of turnip ( Brassica rapa L. subsp. rapa); white lupin ( Lupinus albus L.); and a mixture of black oat and lupin. Two-year conservation-tillage rotational sequences included conventionally tilled continuous corn and cotton winter fallow systems as controls. The 10 conservation-tillage, winter cover-crop systems investigated were three continuous cotton systems that alternated a winter legume (lupin or clover), six cotton-corn systems, where lupin preceded cotton and radish, rape, or turnip preceded corn, and a cotton-corn system that had a lupin-black oat mixture as a winter cover crop every year. Use of lupin or 'AU Robin' clover resulted in weed biomass reduction of up to 80% and 54%, respectively, in weed biomass compared to the fallow system. The highest yielding corn-cotton conservation tillage rotation with a winter cover yielded 200 lbs/acre more that the continuous cotton winter fallow system. Continuous conventional corn with winter fallow yielded 30 bu/acre less than the highest yielding 2-yr, conservation tillage winter crop system.
  • Authors:
    • Mehuys, G. R.
    • Madramootoo, C. A.
    • Burgess, M. S. E.
    • Mehdi, B. B.
    • Dam, R. F.
    • Callum, I. R.
  • Source: Soil & Tillage Research
  • Volume: 84
  • Issue: 1
  • Year: 2005
  • Summary: Different tillage and residue practices could potentially lead to significant differences in both crop production and soil properties, especially if both practices are implemented over a long time period and on continuous monoculture corn (Zea mays L.). The objective of this research was to determine how differing tillage practices and corn residues affected soil bulk density, corn emergence rates and crop yields over an 11-year period. The experimental site consisted of three tillage practices (no-till, NT; reduced tillage, RT; and conventional tillage, CT) and two residue practices (with grain corn residue, R; without residue (corn crop harvested for silage), NR). Bulk density was 10% higher in NT (1.37 Mg m(-3)) than in CT (1.23 Mg m(-3)), particularly at the 0-0.10 m depth. Spring corn emergence in NTR was slower by 14-63% than all other treatments in 1992-1994. In 1996, corn emergence in the NTR treatment was 18-30% slower, and NTNR was 5-30% faster than all other treatments. No-till with residue (NTR) possibly had the slowest overall emergence due to the higher surface residue cover (8.5 Mg ha(-1) in 1996) and higher bulk density (1.37 Mg m(-3) over the 11 years). Long-term mean dry matter corn yields were not affected by tillage and residue practices during the course of this study; rather climatic-related differences seemed to have a greater influence on the variation in dry matter yields. The long-term cropping of corn under different tillage and residue practices can change bulk density in the surface soil layer, vary the corn emergence without affecting yields, and produce comparable yields between all the tillage and residue practices. (C) 2004 Elsevier B.V. All rights reserved.
  • Authors:
    • Gibson, S. G.
    • Yarboro, W.
    • Hamrick, M.
    • Thompson, S.
    • King, R.
  • Source: Proceedings of the 26th Southern Conservation Tillage Conference for Sustainable Agriculture
  • Year: 2004
  • Summary: In addition to regular programming, County Agricultural Extension agents are asked many times to respond to questions, suggestions and concerns by their farmer clientele. In North Carolina as in other states an advisory leadership system is in place and farmers can formally and informally make suggestions and requests for on-farm demonstrational work. In many cases what the farmers are observing in their fields and/or things they have read "spark" the interactions with agents. Such has been the case in Cleveland County, NC. For example in the early continuous no-till era many area farmers were concerned about soil compaction. Measurements and simple demonstrations conducted by the Cleveland and Lincoln County agents and supported by the NCSU Soil Science Department and Cleveland County Government helped alleviate these concerns. Later as fields were in continuous no-till for 5 or more years, farmers began to notice a greater than expected development of their crops prior to major applications of fertilizer nitrogen. These observations led to a replicated test in wheat conducted by the Cleveland County Agricultural Extension agent comparing a field in a 2 year no-till wheat soybean rotation verses a nearby field in a 5 year continuous no-till wheat soybean rotation. Also a 6 year replicated test was initiated on Cleveland County owned land that had been in continuous no-till for 10 years. The test was set up as a continuous soybean corn rotation and in addition to the standard dryland portion, irrigation was used in part of the study to simulate a "good" corn year. Five nitrogen rates were used. The economics of the cost of fertilizer nitrogen was used to demonstrate that the Realistic Yield Expectation (RYE) method for determining nitrogen rates was very much applicable in continuous no-till. Both the wheat and corn tests indicated that residual soil nitrogen was indeed becoming a major factor in continuous no-till for these field crops and when farmers considered the realities of the weather very likely nitrogen rates can be reduced with confidence.
  • Authors:
    • Wienhold, B. J.
    • Tanaka, D. L.
    • Liebig, M. A.
  • Source: Soil & Tillage Research
  • Volume: 78
  • Issue: 2
  • Year: 2004
  • Summary: 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; USDA1: 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 Mgha-1), particulate organic matter C (POM-C) (by 4.98Mgha-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.
  • Authors:
    • Tan, C. S.
    • Reynolds, W. D.
    • Yang, X. M.
    • Drury, C. F.
  • Source: Soil & Tillage Research
  • Volume: 79
  • Issue: 1
  • Year: 2004
  • Summary: The influence of soil and crop management practices on soil aggregation is well documented; however very little information is available on the impact of aggregation on biological processes such as greenhouse gas emissions. Soils (Ap horizon of a Brookston clay loam) were sampled in the spring of 2002 from two treatments in a long-term study (established in 1959). The treatments included continuous corn (Zea mays L.) and the corn phase of a 4-year crop rotation which included corn-oats (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa. The continuous corn (CC) treatment was plowed every fall whereas the rotation corn (RC) treatment was plowed 2 out of the 4 years (in the fall following second year alfalfa and following corn). The objectives were to determine the impact of crop rotation and continuous corn on aggregate size distribution, and the influence of aggregate size on CO2 and N2O production through denitrification. The soil samples were separated into six aggregate size fractions (<0.25, 0.25-0.50, 0.50-1.0, 1.0-2.0, 2.0-4.0, and 4.0-8.0mm diameter) using a dry sieving procedure. Each aggregate size fraction was separated into two subsamples with one subsample left intact and the other ground to <0.15mm (100-mesh sieve). The intact and ground aggregates from each size fraction were incubated anaerobically using the acetylene inhibition technique and carbon dioxide (CO2) and nitrous oxide (N2O) production (denitrification) were determined. Nitrate was added and thus not limiting in the incubations. In both cropping treatments, the 2–4mm aggregate size was the dominant size fraction (~35-45% of the soil by weight) followed by the 1-2mm size fraction (~20-25% of the soil by weight). Crop rotation increased both CO2 and N2O production (denitrification) and the proportion of <2mm diameter aggregates compared to continuous corn. For intact aggregates, CO2 production decreased with increasing aggregate size, while N2O production (denitrification) increased with increasing aggregate size. When the aggregates were ground, CO2 production was independent of the original aggregate size, while N2O production (denitrification) decreased as the size of the original aggregates increased. This study demonstrates that both the size distribution of natural soil aggregates and soil grinding can have substantial impacts on the CO2 and N2O production through denitrification.
  • Authors:
    • USDA-ARS
    • Clapp, C. E.
    • Linden, D. R.
    • Allmaras, R. R.
  • Source: Soil Science Society of America Journal
  • Volume: 68
  • Issue: 4
  • Year: 2004
  • Summary: Soil organic carbon (SOC) is sensitive to management of tillage, residue (stover) harvest, and N fertilization in corn (Zea mays L.), but little is known about associated root biomass including rhizodeposition. Natural C isotope abundance ({delta}13C) and total C content, measured in paired plots of stover harvest and return were used to estimate corn-derived SOC (cdSOC) and the contribution of nonharvestable biomass (crown, roots, and rhizodeposits) to the SOC pool. Rhizodeposition was estimated for each treatment in a factorial of three tillage treatments (moldboard, MB; chisel, CH; and no-till, NT), two N fertilizer rates (200 and 0 kg N ha-1), and two corn residue managements. Treatments influenced cdSOC across a wide range (6.8-17.8 Mg C ha-1). Nitrogen fertilization increased stover C by 20%, cdSOC by only 1.9 Mg C ha-1, and increased rhizodeposition by at least 110% compared with that with no N fertilizer. Stover harvest vs. stover return reduced total source carbon (SC) by 20%, cdSOC by 35%, and total SOC. The amount of stover source carbon (SSC) responded to tillage (MB > CH > NT), but tillage affected the amount of cdSOC differently (NT > CH > MB). Total SOC was maintained only by both N fertilization and stover return during the 13-yr period. The ratio of SC in the nonharvestable biomass to SSC ranged from 1.01 to 3.49; a ratio of 0.6 conforms to a root-to-shoot ratio of 0.4 when the root biomass includes 50% rhizodeposits. Tillage controlled the fraction of SC retained as cdSOC (i.e., humified; 0.26 for NT and 0.11 for MB and CH), even though N fertilization, stover harvest, and tillage all significantly influenced SC. Decomposition of labile rhizodeposits was a major component of the nonhumified fraction. Rhizodeposition was as much as three times greater than suggested by laboratory and other controlled studies. To understand and manage the entire C cycle, roots and rhizodeposition must be included in the analysis at the field level.