• Authors:
    • Tanni, R.
    • Pietola, L.
  • Source: Agricultural and Food Science in Finland
  • Volume: 8
  • Issue: 4/5
  • Year: 1999
  • Summary: The role of plant growth regulators (PGR) in nitrogen (N) fertilization of spring wheat and oats (CCC [chlormequat]), fodder barley (etephon/mepiquat) an oilseed rape (etephone) in crop rotation was studied in 1993-96 on loamy clay soil. Carry over effect of the N fertilization rates (0-180 kg/ha) was evaluated in 1997. N fertilization rate for the best grain/seed yield (120-150 kg/ha) was not affected by PGRs. The seed and N yields of oilseed rape were improved frequently by the recommended use of PGR. The yield of oats increased in 1995-96. Even though PGR effectively shortened the plant height of spring wheat, the grain yield increased only in 1995. N yield of wheat grains was not increased. Response of fodder barley to PGR was insignificant or even negative in 1995. The data suggest that PGRs may decrease some N leaching at high N rates by improving N uptake by grain/seeds, if the yield is improved. The carryover study showed that in soils with no N fertilization, as well as in soils of high N rates, N uptake was higher than in soils with moderate N fertilization (60-90 kg/ha), independent of PGRs. According to soil mineral N contents, N leaching risk was significant (15-35 kg/ha) only after dry and warm late seasons. After a favourable season of high yields, the N rates did not significantly affect soil mineral N contents.
  • Authors:
    • Collins, C.
    • Chalmers, A. G.
    • Froment, M. A.
    • Grylls, J. P.
  • Source: The Journal of Agricultural Science
  • Volume: 133
  • Year: 1999
  • Summary: The effect of a range of one-year set-aside treatments on soil mineral nitrogen (SMN), during the set-aside period and in a following wheat crop were studied in a phased experiment at five sites from 1987 to 1991. Ground cover options permitted under the UK government's 'set-aside' scheme, including natural regeneration, autumn sown Italian ryegrass (Lolium multiflorum), spring-sown legumes and cultivated fallow, were compared with a control treatment of continuous cereals managed with fertilizer inputs. In the first of three phases in this experiment, an uncultivated fallow (kept weed-free) and autumn-sown forage rape (Brassica napus) were included as extra treatments. There were large differences in total SMN (0.0-0.9 m) between sites, ranging from 16 to 205 kg N/ha, reflecting differences in soil type, which ranged from clays to sands, and previous cropping husbandry. Differences in SMN between set-aside treatments during the first winter of the set-aside year were small, but increased during the following summer. Amounts of SMN were greatest after cultivated fallow (46-178 kg N/ha) and least after ryegrass (26-111 kg N/ha). Natural regeneration and spring sown legumes were more variable in their effect on SMN. Compared to continuous cereals, there was a build up in SMN during bare fallow, but a reduction under ryegrass, prior to returning to wheat cropping in the autumn after set-aside. SMN results suggest there was an increased nitrate leaching risk for bare fallow and natural regeneration set-aside, compared to sown ryegrass covers, in the winter following ploughing out of set-aside. This risk could be minimized by earlier sowing of winter cereals following set-aside or sowing with winter oilseed rape rather than cereals to maximize crop nitrogen (N) uptake, during the autumn growth period. Averaged across five sites, residual SMN supply in the spring of first test year cereal crops for all set-aside treatments was similar to that for continuous cereals, suggesting over-winter losses by N leaching or immobilization. The low residual N fertility after rotational set-aside suggested that following crop N recommendations should be the same as for continuous cereals. Amounts of SMN were less each year in spring than in the preceding autumn in both the set-aside and first test cereal crops. The results suggested that a ryegrass cover appeared to be the most environmentally favourable option for rotational set-aside management, as it minimized the amount of readily leachable N both during and immediately after the set-aside period.
  • Authors:
    • Avci, M.
  • Source: Efficient soil water use: the key to sustainable crop production in the dry areas of West Asia, and North and Sub-Saharan Africa. Proceedings of the workshops organized by the Optimizing Soil Water Use Consortium, Niamey, Niger, 26-30 April, 1998, Amman, J
  • Year: 1999
  • Summary: Semi-arid areas cover about 55% of Turkey and are mainly found in the Central Anatolian Plateau. The main crop production systems are fallow/wheat and legume/wheat. Wheat is generally prone to droughts, which severely affect the yields. Research on soil moisture use in fallow-wheat systems started in the 1930s. Its focus was on water interception and conservation techniques, and detailed research on rainfall interception led to practices which have been adopted by most of the plateau farmers. In the 1980s research focused on the replacement of fallow by a crop in the rotation systems. In most areas, fallow can best be replaced in terms of yield by forage crops and economically by edible legumes. Characterization of the other regions will identify fallow or continuous cropping target areas, and extrapolation of research results to them. Regarding technologies, the importance of terracing for moisture conservation increases with the degree of slope and the occurrence of erosive rainfall. Contour tillage and sowing were effective only on steep slopes. Future research is needed on supplemental irrigation to increase the water-use efficiencies of the wheat and barley varieties especially developed for irrigation.
  • Authors:
    • Whitney, D.
    • Thompson, C.
  • Source: Journal of Production Agriculture
  • Volume: 11
  • Issue: 3
  • Year: 1998
  • Summary: Tillage and N management are important in dryland crop production of the west central Great Plains (area between the 99(th) meridian and the eastern edge of the Rocky Mountains) because of frequent periods of limited soil moisture. Therefore, judicious use of N fertilizer is a management priority in wheat (Triticum aestivum L,)-sorghum [Sorghum biocolor (L,) Moench]- fallow (W-S-F) rotations. The objectives of this study were to: (i) determine the long-term effects of N fertilization (0, 20, 40, and 60 lb N/acre) on grain yields of winter wheat and grain sorghum under three tillage systems, (ii) investigate the effect of soil moisture at or near planting on grain yields, and (iii) evaluate the residual profile soil inorganic N after 20 yr of N fertilization in the three tillage systems. The study involved a W-S-F rotation under three tillage systems on a nearly level Harney silt loam soil (fine, montmorillonite, mesic Typic Argiustoll), The three tillage systems were clean-till (CT), reduced-till (RT), and no-till (NT), Nitrogen was broadcast preplant as ammonium nitrate on each crop at rates of 0, 20, 40, and 60 Ib N/acre, As the level of soil moisture increased in each tillage system, there was a corresponding larger yield increase of wheat and sorghum to applied N, The correlation of grain yields of wheat and sorghum with soil profile N at all depths was highest for nitrate N and lowest for ammonium and total inorganic N. For all three tillage systems, sampling deeper than 6 in, resulted in little improvement in the coefficient of determination (R-2) for grain yields regressed on soil nitrate N, Residual soil nitrate N was highest in the top 6 in., dropped significantly in the 6- to 12-in. depth, and remained relatively low thereafter throughout the 72-in. sampling depth. Data from this long-term study showed the optimum broadcast N rate was approximately 60 Ib N/acre applied on each crop grown in a W-S-F rotation with the exact rate depending on soil moisture, fertilizer, and crop prices, Yields from CT were comparable with RT on this nearly level upland soil but failed to meet the residue requirements mandated in conservation compliance plans, Poorer stands, increased weed competition, and drier soils resulted in generally lower yields from NT plots. Considering all factors, RT systems for dryland wheat and sorghum production are recommended on upland fertile soils in the west central Great Plains.
  • Authors:
    • Bowman, R. A.
    • Halvorson, A. D.
  • Source: Soil Science
  • Volume: 163
  • Issue: 3
  • Year: 1998
  • Summary: Intensively cropped dryland systems in the central Great Plains require adequate N fertilization for optimum residue and grain production. However, this N fertilization could be slowly changing the chemistry of the surface soil because of a decrease in soil pH and an increase in soil organic matter (SOM) and basic cations, even in previously well buffered calcareous soil systems. We investigated the effects of five increasing ammonium-N fertilizer rates in a Platner loam, on physical and chemical changes at the 0 to 5, and 0 to 15-cm depths after three cycles of no-till wheat (Triticum aestivum L.)-corn (Zea mays L.)-fallow rotation. The measured soil pH, texture, bulk density, cation exchange capacity (CEC), total P, soluble and total soil organic carbon (SOC), nitrate-N to a depth of 60 cm, and grain yields. No significant changes were found with soil texture, bulk densities, CEC, and total P. The data showed a significant reduction in surface (0-5 cm) soil pH (6.5 to 5.1) with the highest N rate (112 kg/ha), but this was accompanied by a 40% increase in SOC. Although there were significant increases in Al and Mn and decreases in Ca concentrations in the surface 0 to 5 cm at the highest N rate, no reduction in grain yields occurred relative to lower N levels with near neutral pHs. Because only a shallow depth of the soil was affected, residue, SOM, and rapid root growth could be compensating for surface acidity, Over the longer term, we need to monitor the effects of ammoniacal-N on downward soil acidity and yield trends under these new intensive cropping systems.
  • Authors:
    • Lyon, D. J.
    • Tanaka, D. L.
    • Jones, O. R.
    • Havlin, J. L.
    • Halvorson, A. D.
    • Peterson, G. A.
    • Pennock, D. J.
  • Source: Soil & Tillage Research
  • Volume: 47
  • Issue: 3
  • Year: 1998
  • Summary: Concern about soil organic matter losses as a result of cultivation has been voiced consistently since the early part of the 20th century. Scientists working in the U.S. Great Plains recognized that organic matter losses from an already small pool could have major negative consequences on soil physical properties and N supplying capacity. The advent of reduced- and no-till systems has greatly improved our ability to capture and retain precipitation in the soil during the non-crop periods of the cropping cycle, and has made it possible to reduce fallow frequency and intensify cropping systems. The purpose of this paper is to summarize the effects of reduced tillage and cropping system intensification on C storage in soils using data from experiments in North Dakota, Nebraska, Kansas, Colorado, and Texas. Decades of farming with the wheat (Triticum aestivum L.)-fallow system, the dominant farming system in the Great Plains, have accentuated soil C losses. More intensive cropping systems, made possible by the greater water conservation associated with no-till practices, have produced more grain, produced more crop residue and allowed more of it to remain on the soil surface. Combined with less soil disturbance in reduced- and no-till systems, intensive cropping has increased C storage in the soil. We also conclude that the effects of cropping system intensification on soil C should not be investigated independent of residue C still on the surface. There are many unknowns regarding how rapidly changes in soil C will occur when tillage and cropping systems are changed, but the data summarized in this paper indicate that in the surface 2.5 cm of soil, changes can be detected within 10 years. It is imperative that we continue long-term experiments to evaluate rates of change over an extended period. It is also apparent that we should include residue C, both on the surface of the soil and within the surface 2.5 cm, in our system C budgets if we are to accurately depict residue±soil C system status. The accounting of soil C must be done on a mass basis rather than on a concentration basis.
  • Authors:
    • Bowman, R. A.
    • Schuman, G. E.
    • Reeder, J. D.
  • Source: Soil & Tillage Research
  • Volume: 47
  • Issue: 3-4
  • Year: 1998
  • Summary: The Conservation Reserve Program (CRP) was initiated to reduce water and wind erosion on marginal, highly erodible croplands by removing them from production and planting permanent, soil-conserving vegetation such as grass. We conducted a field study at two sites in Wyoming, USA, in order to quantify changes in soil C and N of marginal croplands seeded to grass, and of native rangeland plowed and cropped to wheat-fallow. Field plots were established on a sandy loam site and a clay loam site on wheat-fallow cropland that had been in production for 60+ years and on adjacent native rangeland. In 1993, 6 years after the study was initiated, the surface soil was sampled in 2.5 cm depth increments, while the subsurface soil was composited as one depth increment. All soil samples were analyzed for total organic C and N, and potential net mineralized C and N. After 60+ years of cultivation, surface soils at both study sites were 18-26% lower (by mass) in total organic C and N than in the A horizons of adjacent native range. Six years after plowing and converting native rangeland to cropland (three wheat-fallow cycles), both total and potential net mineralized C and N in the surface soil had decreased and NO3-N at all depths had increased to levels found after 60+ years of cultivation. We estimate that mixing of the surface and subsurface soil with tillage accounted for 40-60% of the decrease in surface soil C and N in long-term cultivated fields; in the short-term cultivated fields, mixing with tillage may have accounted for 60-75% of the decrease in C, and 30-60% of the decrease in N. These results emphasize the need to evaluate C and N in the entire soil solum, rather than in just the surface soil, if actual losses of C and N due to cultivation are to be distinguished from vertical redistribution. Five years after reestablishing grass on the sandy loam soil, both total and potential net mineralized C and N in the surface soil had increased to levels equal to or greater than those observed in the A horizon of the native range. On the clay loam soil, however, significant increases in total organic C were observed only in the surface 2.5 cm of N-fertilized grass plots, while total organic N had not significantly increased from levels observed in the long-term cultivated fields.
  • Authors:
    • Burke, I. C.
    • Robles, M. D.
  • Source: Soil Science Society of America Journal
  • Volume: 62
  • Issue: 3
  • Year: 1998
  • Summary: Soil C and N changes following cessation of cultivation in semiarid soils is not well understood. We hypothesized that returning cultivated fields in southeastern Wyoming to perennial grasses through the Conservation Reserve Program (CRP) would (i) increase labile pools of soil organic matter (SOM), and (ii) increase small-scale heterogeneity of SOM. Carbon and N in labile and passive pools of SOM were measured in CRP fields seeded with perennial grasses intermediate wheatgrass (Elytrigia intermedia [Host] Nevski ssp. intermedia), pu- bescent wheatgrass (Elytrigia intermedia [Schur.] A. Love ssp. barbu- lata) and smooth brome (Bromus inermis Leysser), and in winter wheat (Triticum aestivum L.)-fallow fields. Mineralizable C increased from 0.37 g m~2 d-1 in wheat-fallow fields to 0.99 g m~2d-1 in CRP fields; mineralizable N and coarse particulate C were consistently but not significantly higher in CRP fields. Fine particulate and total soil C and IN were not significantly different between CRP and wheat-fallow. Within CRP fields, mineralizable C was significantly higher under grasses than in interspaces (1.96 vs. 0.73 g m-2 d-1, respectively), and mineralizable N and coarse particulate C and N were consistently but not significantly higher under grasses than in interspaces. Soil C and N have increased only slightly after 6 yr of CRP management, and future changes in land use management on these CRP fields, including grazing and cropping, may accrue some small benefits associated with improved soil fertility status.
  • Authors:
    • Heinemeyer, O.
    • Lyon, D. J.
    • Drijber, R. A.
    • Doran, J. W.
    • Mosier, A. R.
    • Kessavalou, A.
  • Source: Journal of Environmental Quality
  • Volume: 27
  • Issue: 5
  • Year: 1998
  • Summary: Cropping and tillage management can increase atmospheric CO2, N2O, and CH4 concentrations, and contribute to global warming and destruction of the ozone layer. Fluxes of these gases in vented surface chambers, and water-filled pore space (WFPS) and temperature of survace soil were measured weekly from a long-term winter wheat (Triticum aestivum L.)-fallow rotation system under chemical (no-tillage) and mechanical tillage (noninversion subtillage at 7 to 10 cm or moldboard plowing to 15 cm) follow management and compared with those from "native" grass sod at Sidney, NE, from March 1993 to July 1995. Cropping, tillage, within-field location, time of year, soil temperature, and WFPS influenced net greenhouse gas fluxes. Mean annual interrow CO2 emissions from wheat-fallow ranged from 6.9 to 20.1 kg C ha-1 d-1 and generally increased with intensity and degree of tillage (no-till least and plow greatest). Nitrous oxide flux averaged summer > autumn > winter. Winter periods accounted for 4 to 10% and 3 to 47% of the annual CO2 and N2O flux, respectively, and 12 to 21% of the annual CH4 uptake. Fluxes of CO2 and N2O, and CH4 uptake increased linearly with soil temperature. No-till fallow exhibited the least threat to deterioration of atmospheric or soil quality as reflected by greater CH4 uptake, decreased N2O and CO2 emissions, and less loss of soil organic C than tilled soils. However, potential for increased C sequestration in this wheat-fallow system is limited due to reduced C input from intermittent cropping.
  • Authors:
    • Ortiz-Monasterio, I.
    • Naylor, R.
    • Matson, P. A.
  • Source: Science
  • Volume: 280
  • Issue: 5360
  • Year: 1998
  • Summary: Nitrogen fertilization is a substantial source of nitrogen-containing trace gases that have both regional and global consequences, In the intensive wheat systems of Mexico, typical fertilization practices lead to extremely high fluxes of nitrous oxide (N2O) and nitric oxide (NO). In experiments, lower rates of nitrogen fertilizer, applied later in the crop cycle, reduced the loss of nitrogen without affecting yield and grain quality. Economic analyses projected this alternative practice to save 12 to 17 percent of after-tax profits, A knowledge-intensive approach to fertilizer management can substitute for higher levels of inputs, saving farmers money and reducing environmental costs.