Showing papers in "Agronomy Journal in 2005"

Evaluating Cover Crops for Benefits, Costs and Performance within Cropping System Niches

Abstract: The integration of cover crops into cropping systems brings costs and benefits, both internal and external to the farm. Benefits include promoting pest-suppression, soil and water quality, nutrient cycling efficiency, and cash crop productivity. Costs of adopting cover crops include increased direct costs, potentially reduced income if cover crops interfere with other attractive crops, slow soil warming, difficulties in predicting N mineralization, and production expenses. Cover crop benefits tend to be higher in irrigated systems. The literature is reviewed here along with Michigan farmer experience to evaluate promising cover crop species for four niches: Northern winter (USDA Hardiness Zones 5-6), Northern summer (Zones 5-6), Southern winter (Zones 7-8), and Southern summer (Zones 7-8). Warm season C 4 grasses are outstanding performers for summer niches (6-9 Mg ha -1 ), and rye (Secale cereale L.) is the most promising for winter niches (0.8-6 Mg ha -1 ) across all hardiness zones reviewed. Legume-cereal mixtures such as sudangrass (Sorghum sudanese L.)-cowpea (Vigna unguiculata L.) and wheat (Triticum aestivum L.)-red clover (Trifolium pretense L.) are the most effective means to produce substantial amounts (28 Mg ha -1 ) of mixed quality residues. Legume covers are slow growers and expensive to establish. At the same time, legumes fix N, produce high quality but limited amounts (0.5-4 Mg ha -1 ) of residues, and enhance beneficial insect habitat. Brassica species produce glucosinolate-containing residues (2-6 Mg ha -1 ) and suppress plant-parasitic nematodes and soil-borne disease. Legume cover crops are the most reliable means to enhance cash crop yields compared with fallows or other cover crop species. However, farmer goals and circumstances must be considered. If soil pests are a major yield limiting factor in cash crop production, then use of brassica cover crops should be considered. Cereal cover crops produce the largest amount of biomass and should be considered when the goal is to rapidly build soil organic matter. Legume-cereal or brassica-cereal mixtures show promise over a wide range of niches.

The Contribution of Commercial Fertilizer Nutrients to Food Production

Abstract: technology and intensified production often involve a greater need for commercial fertilizer nutrients to avoid Nutrient inputs in crop production systems have come under innutrient depletion and ensure soil quality and crop procreased scrutiny in recent years because of the potential for environductivity. The need for increased inputs correctly raises mental impact from inputs such as N and P. The benefits of nutrient inputsareoftenminimizedindiscussionsofpotentialrisk.Thepurpose questions about associated risks. Potential risks are ofof this article is to examine existing data and approximate the effects ten widely publicized while the associated benefits of of nutrient inputs, specifically from commercial fertilizers, on crop an abundant, affordable, and healthful food supply can yield. Several long-term studies in the USA, England, and the tropics, be overlooked or understated. To judge any such pracalong with the results from an agricultural chemical use study and ticeorsystem,therisksmustbeevaluatedincomparison nutrient budget information, were evaluated. A total of 362 seasons with the benefits. While misuses of agricultural fertilizof crop production were included in the long-term study evaluations. ers have undoubtedly occurred and concerns about how Crops utilized in these studies included corn (Zea mays L.), wheat fertilizers affect the environment have sometimes been (Triticum aestivum L.), soybean [Glycine max (L.) Merr.], rice (Oroverstated, the purpose of this article is not to address yza sativa L.), and cowpea [Vigna unguiculata (L.) Walp.]. The these issues but to provide evidence of the impact comaverage percentage of yield attributable to fertilizer generally ranged from about 40 to 60% in the USA and England and tended to be mercial fertilizers have had on agricultural production. much higher in the tropics. Recently calculated budgets for N, P, and Several attempts have previously been made to estiKindicatethatcommercialfertilizer makesupthemajorityofnutrient mate how much of the crop production in the USA is inputs necessary to sustain current crop yields in the USA. The results attributable to commercial nutrient inputs. These estiof this investigation indicate that the commonly cited generalization mates usually range from about 30 to 50% for major that at least 30 to 50% of crop yield is attributable to commercial grain crops (Nelson, 1990). Determining these estimates fertilizer nutrient inputs is a reasonable, if not conservative estimate. presents significant challenges, and assumptions are always required regardless of the approach taken. One difficulty that arises is that crops respond differently to M

Aerial Color Infrared Photography for Determining Early In-Season Nitrogen Requirements in Corn

Abstract: In-season determination of corn (Zea mays L.) N requirements via remote sensing may help optimize N application decisions and improve profit, fertilizer use efficiency, and environmental quality. The objective of this study was to use aerial color-infrared (CIR) photography as a remote-sensing technique for predicting in-season N requirements for corn at the V7 growth stage. Field studies were conducted for 2 yr at three locations, each with and without irrigation, in the North Carolina Coastal Plain. Experimental treatments were a complete factorial of four N rates at planting (N PL ) and five N rates at V7 (N V7 ). Aerial CIR photographs were taken at each of the locations at V7 before N application. Optimum N V7 ranged from 0 to 207 kg N ha -1 with a mean of 67 kg N ha -1 . Significant but weak correlations were observed between optimum N V7 rates and the band combinations relative green, Relative Green Difference Vegetation Index, and Relative Difference Vegetation Index as measured in CIR photos. High proportions of soil reflectance in the images early in the corn growing season (V7) likely confounded our attempts to relate spectral information to optimum N V7 rates. The primary obstacles to applying this technique early in the season are the use of relative digital counts or indices that require high-N reference strips in the field and strong background reflectance from the soil. When the N PL treatments that were nonresponsive to N V7 (i.e., optimum N V7 =0) were removed from the analysis, the normalized near infrared, the Green Difference Vegetation Index, the Green Ratio Vegetation Index, and the Green Normalized Difference Vegetation Index were the best predictors of optimum N V7 rate (r 2 = 033).

DIALLEL‐SAS05: A Comprehensive Program for Griffing's and Gardner–Eberhart Analyses

Abstract: Diallel mating designs provide to breeders useful genetic information, such as general combining ability (GCA) and specific combining ability (SCA), to help them devise appropriate breeding and selection strategies. Here we report a much-improved version of DIALLEL-SAS that was originally released in 1997. The new program, DIALLEL-SAS05 has a clear and user-friendly interface that was designed to meet users' needs for various diallel-cross design experiments. DIALLEL-SAS05 has major advantages over DIALLEL-SAS in that: (i) it analyzes not only all four Grifflng's diallel methods (both fixed and random models), but it also computes Gardner-Eberhart's Analyses II and III; (ii) it provides desired results from diallel experiments with parent number from 4 to 12, (iii) it can analyze diallel data from any number of environments, and (iv) for a random-effects model, it provides estimates of GCA (σ 2 g ) and SCA (or,2) variances, which can be used to estimate additive (σ 2 A ) and dominance (σ 2 D ) variances, and ultimately narrow-sense heritability (h 2 ). DIALLEL-SAS05 also provides information on GCA x ENV, SCA x ENV, reciprocal x ENV, maternal x ENV, and nonmaternal x ENV interactions, when applicable. DIALLEL-SAS05 should greatly improve researchers' efficiency in analyzing and interpreting diallel-cross data. The program code is available on a CD from the corresponding author.

Remotely measuring chlorophyll content in corn leaves with differing nitrogen levels and relative water content

Abstract: Measuring a crop's physiological parameters provides information for interpreting its response to the environment. Remote sensing is quickly becoming recognized as a valuable tool that has the potential to assess a wide variety of physiological properties over a large area in a short amount of time. This study examined the relationship of corn (Zea mays L.) leaf spectral response to its chlorophyll content and relative water content. The effects of N stress and water stress were examined on each of these physiological parameters. Over the years, several spectral indices have been introduced for a wide variety of applications. A number of these indices were evaluated for their ability to predict the parameters in question. The normalized difference between the first derivatives at 525 and 570 nm, as well as the wavelength location of the red edge, showed a strong association with chlorophyll content (r 2 = 0.81 and 0.80, respectively). Even stronger relationships to chlorophyll content were observed with the ratios of 600/680 nm (r 2 = 0.83) and 630/680 nm (r 2 = 0.83). Thus, our results suggest that spectral reflectance measurements hold promise for the assessment of some physiological parameters at the leaf level. Further investigation is needed to evaluate the effectiveness of such techniques at the canopy level.

Maize Radiation Use Efficiency under Optimal Growth Conditions

Abstract: Accurate measurement of crop growth and radiation use efficiency (RUE) under optimal growth conditions is required to predict plant dry matter accumulation and grain yield near the genetic growth potential. Research was conducted to quantify the biomass and leaf area index (LAI) accumulation, extinction coefficient, and RUE of maize (Zea mays L.) under conditions of optimal growth. Maize was grown in two environments over five growing seasons (1998-2002). Total aboveground biomass at maturity ranged from 2257 g m -2 in 1998 to 2916 g m -2 in 2001; values that are considerably greater than the biomass achieved in most previous studies on RUE in maize. Peak LAI ranged from 4.8 to 7.8. Maize extinction coefficients during vegetative growth (k) were within the range of recently published values (0.49 ± 0.03), with no clear pattern of differences in k among years. Seasonal changes in interception of photosynthetically active radiation (PAR) were similar across all but one year. Estimates of RUE were obtained using the short-interval crop growth rate method and the cumulative biomass and absorbed PAR (APAR) method. Values of RUE obtained using the two methods were 3.74 (±0.20) g MJ -1 APAR and 3.84 (±0.08) g MJ -1 APAR, respectively, and did not vary among years. This compares to a published mean RUE for maize of 3.3 g MJ -1 of intercepted PAR (Mitchell et al., 1998). Moreover, RUE did not decline during grain filling. Differences in biomass accumulation among years were attributed in part to differences in observed radiation interception, which varied primarily due to differences in LAI. Maize simulation models that rely on RUE for biomass accumulation should use an RUE of 3.8 g MJ -1 APAR for predicting optimum yields without growth limitations.

Temporal and Spatial Relationships between within-field Yield variability in Cotton and High-Spatial Hyperspectral Remote Sensing Imagery

Abstract: The authors gratefully acknowledge the NASA/USDA jointly funded AG20/20 project for funding image acquisitions.

Field-scale variability in optimal nitrogen fertilizer rate for corn

Abstract: Applying only as much N fertilizer as is needed by a crop has economic and environmental benefits. Understanding variability in need for N fertilizer within individual fields is necessary to guide approaches to meeting crop needs while minimizing N inputs and losses. Our objective was to characterize the spatial variability of corn (Zea mays L.) N need in production corn fields. Eight experiments were conducted in three major soil areas (Mississippi Delta alluvial, deep loess, clay-pan) over 3 yr. Treatments were field-length strips of discrete N rates from 0 to 280 kg N ha - 1 . Yield data were partitioned into 20-m increments, and a quadratic-plateau function was used to describe yield response to N rate for each 20-m section. Economically optimal N fertilizer rate (EONR) was very different between fields and was also highly variable within fields. Median EONR for individual fields ranged from 63 to 208 kg N ha - 1 , indicating a need to manage N fertilizer differently for different fields. In seven of the eight fields, a uniform N application at the median EONR would cause more than half of the field to be over- or underfertilized by at least 34 kg N ha - 1 . Coarse patterns of spatial variability in EONR were observed in some fields, but fine and complex patterns were also observed in most fields. This suggests that the use of a few appropriate management zones per field might produce some benefits but that N management systems using spatially dense information have potential for greater benefits. Our results suggest that further attempts to develop systems for predicting and addressing spatially variable N needs are justified in these production environments.

Efficient Water Use in Dryland Cropping Systems in the Great Plains

Abstract: Successful dryland crop production in the semiarid Great Plains of North America must make efficient use of precipitation that is often limited and erratic in spatial and temporal distribution. The purpose of this paper is to review research on water use efficiency and precipitation use efficiency (PUE) as affected by cropping system and management in the Great Plains. Water use efficiency and PUE increase with residue management practices that increase precipitation storage efficiency, soil surface alterations that reduce runoff, cropping sequences that minimize fallow periods, and use of appropriate management practices for the selected crop. Precipitation use efficiency on a mass-produced basis is highest for systems producing forage (14.5 kg ha - 1 mm - 1 ) and lowest for rotations with a high frequency of oilseed crops (4.2 kg ha - 1 mm - 1 ) or continuous small-grain production in the southern plains (2.8 kg ha - 1 mm - 1 ). Precipitation use efficiency when calculated on a price-received basis ranges from $1.20 ha - 1 mm - 1 (for an opportunity-cropped system with 4 of 5 yr in forage production in the southern plains) to $0.30 ha - 1 mm - 1 {for a wheat (Triticum aestivum L.)-grain sorghum [Sorghum bicolor (L.) Moench]-fallow system in the southern plains}. Throughout the Great Plains region, PUE decreases with more southern latitudes for rotations of similar makeup of cereals, pulses, oilseeds, and forages. Forage systems in the southern Great Plains appear to be highly efficient when PUE is computed on a price-received basis. In general across the Great Plains, increasing intensity of cropping increases PUE on both a mass-produced basis and on a price-received basis.

Improved Water Use Efficiency Associated with Cultivars and Agronomic Management in the North China Plain

Abstract: Both winter wheat (Triticum aestivum L.) and maize (Zea mays L.) are the two staple crops of the North China Plain (NCP) that are combined in a single-year rotation. While annual evapotranspiration increased slightly, field studies conducted at Luancheng Station indicated that crop yield improved by 50% and resulted in significant water use efficiency (WUE) increases from 1982 to 2002. Water use efficiency has improved from 10 to 15 kg mm -1 ha -1 for winter wheat and from 14 to 20 kg mm -1 ha -1 for maize in the Piedmont of Mt. Taihang in the NCP. Yield increase was associated with the increase in kernel numbers per unit area without alteration of the weight of the kernels for both winter wheat and maize. Number of kernels per spike of winter wheat was increased from about 22 for cultivars used in 1980s to about 28 for cultivars used presently. Number of kernels per ear of maize was increased from about 300 for cultivars used in 1980s to about 450 presently. From the early 1990s, combine had been used to harvest winter wheat, allowing straw mulch to be applied to maize. Measurements of WUE from 1987 to 1992 and again from 1997 to 2002 showed that WUE of maize under mulch was significantly higher than that without mulch. Mulching reduced soil evaporation loss by 40 to 50 mm per annum measured by microlysimeters, and WUE was averagely improved 8 to 10% for the 12 seasons, An improvement in irrigation scheduling had also improved WUE. Irrigation applications to winter wheat were reduced from about eight times in 1980s to about four times presently. Field tests from 1999 to 2004 still showed that reducing the present number of seasonal wheat irrigations to either three, two, or one depending on seasonal rainfall would benefit both grain production and WUE of winter wheat.

Remote sensing the spatial distribution of crop residues

Abstract: Management of plant litter or crop residues in agricultural fields is an important consideration for reducing soil erosion and increasing soil organic C. Current methods of quantifying crop residue cover are inadequate for characterizing the spatial variability of residue cover within fields and across large regions. Our objectives were to evaluate several spectral indices for measuring crop residue cover using ground-based and airborne hyperspectral data and to categorize soil tillage intensity in agricultural fields based on crop residue cover. Reflectance spectra of mixtures of crop residues, green vegetation, and soil were acquired over the 400- to 2500-nm wavelength region. High-altitude AVIRIS (Airborne Visible Infrared Imaging Spectrometer) data were also acquired near Beltsville, MD, in May 2000. Broad absorption features near 2100 and 2300 nm in the reflectance spectra of crop residues were associated with cellulose and lignin. These features were not evident in the spectra of green vegetation and soils. Crop residue cover was linearly related to the cellulose absorption index, which was defined as the relative depth of the 2100-nm absorption feature. Other spectral indices for crop residue were calculated and evaluated. The best spectral indices were based on relatively narrow (10-50 nm) bands in the 2000- to 2400-nm region, were linearly related to crop residue cover, and correctly identified tillage intensity classes in >90% of test agricultural fields. Regional surveys of soil management practices that affect soil conservation and soil C dynamics may be feasible using advanced multispectral or hyperspectral imaging systems.

Long-Term Effects of Recycled Wastewater Irrigation on Soil Chemical Properties on Golf Course Fairways

Abstract: The increasing water shortage in the arid and semiarid western USA requires use of recycled wastewater (RWW) when possible. Recycled wastewater has become a common water source for irrigating golf courses and urban landscapes, creating the need to study the effects of RWW irrigation on soil chemical properties. We compiled soil test data from fairways of 10 golf courses that were near metropolitan Denver and Fort Collins, CO. Among these courses, five had been irrigated exclusively with domestic RWW [electrical conductivity (EC) = 0.84 dS m -1 ] for 4, 13, 14, 19, and 33 yr, respectively. The other five with similar turf species, age ranges, and soil textures had used surface water (EC = 0.23 dS m -1 ) for irrigation. Our results indicated that soils (sampled to 11.4 cm) from fairways with RWW irrigation exhibited 03 units of higher pH and 200,40, and 30% higher concentrations of extractable Na, B, and P, respectively. Compared with sites irrigated with surface water, sites irrigated with RWW exhibited 187% higher EC and 481% higher sodium adsorption ratio (SAR). Comparison of soil chemical properties before and 4 or 5 yr after RWW irrigation on two golf courses also revealed the following findings: (i) 89 to 95% increase in Na content; (ii) 28 to 50% increase in B content; and (iii) 89 to 117% increase in P content at the surface depth. Regular monitoring of site-specific water and soil and appropriate management are needed to mitigate the negative impacts of sodium and salts accumulations.

Biculture Legume–Cereal Cover Crops for Enhanced Biomass Yield and Carbon and Nitrogen

Abstract: Biculture legume-cereal cover cropping may enhance above- and belowground biomass yields and C and N contents. The increase in C and N supply to the soil has the potential to improve soil quality and crop productivity compared with monoculture cover crop species. We examined above- and belowground (0- to 120-cm soil depth) biomass yields and C and N contents of a legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], and biculture of legume and nonlegume (vetch and rye) cover crops planted without tillage in the fall of 1999 to 2001 in central Georgia. After cover crop kill in the spring, cotton (Gossypium hitsutum L.) and sorghum [Sorghum bicolor (L.) Moench)] were planted using three tillage practices (no-till, strip till, and chisel till) with three N fertilization rates (0, 60 to 65, and 120 to 130 kg N ha '). The field experiment was arranged in a split-split plot. treatment with three replications on a Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults). Aboveground biomass yield of rye decreased from 6.1 to 2.3 Mg ha ' from 2000 to 2002, but yield of hairy vetch varied (2.4 to 5.2 Mg ha -1 ). In contrast, biomass yield of vetch and rye biculture (5.6 to 8.2 Mg ha -1 ) was greater than that of rye and vetch planted alone in all years. Compared with winter weeds in no cover crop treatment, C content in rye (1729 to 2670 kg ha -1 ') was greater due to higher biomass yield, but N content in vetch (76 to 165 kg ha -1 ) was greater due to higher N concentration, except in 2002. As a result, C (2260 to 3512 kg ha -1 ) and N (84 to 310 kg ha -1 ) contents in biculture were greater than those from monocultures in all years. Similarly, belowground biomass yield and C and N contents were greater in biculture than in monocultures. In 2001, aboveground biomass yield and C and N contents in coyer crops were also greater in strip till with biculture than in other treatments, except in chisel till with vetch and biculture, but belowground biomass yield and N content were greater in chisel till with biculture than in no-till, strip till, and chisel till with weeds. Cotton lint yield was lower with biculture than with rye, but sorghum grain yield and cotton and sorghum biomass (stems + leaves) yields and N uptake were greater with biculture than with rye. Because of higher biomass yield and C and N contents, biculture of hairy vetch and rye cover crops may increase N supply, summer crop yields, and N uptake compared with rye and may increase potentials to improve soil organic matter and reduce N leaching compared with vetch.

Combining field surveys, remote sensing, and regression trees to understand yield variations in an irrigated wheat landscape

Abstract: Improved understanding of the factors that limit crop yields in farmers' fields will play an important role in increasing regional food production while minimizing environmental impacts. However, causes of spatial variability in crop yields are poorly known in many regions because of limited data availability and analysis methods. In this study, we assessed sources of between-field wheat (Triticum aestivum L.) yield variability for two growing seasons in the Yaqui Valley, Mexico. Field surveys conducted in 2001 and 2003 provided data on management practices for 68 and 80 wheat fields throughout the Valley, respectively, while yields on these fields were estimated using concurrent Landsat satellite imagery. Management-yield relationships were analyzed with t tests, linear regression, and regression trees, all of which revealed significant but year-dependent impacts of management on yields. In 2001, an unusually cool year that favored high yields, N fertilizer was the most important source of between-field variability. In 2003, a warmer year with reduced irrigation water allocations, the timing of the first postplanting irrigation was found to be the most important control. Management explained at least 50% of spatial yield variability in both years. Regression tree models, which were able to capture important nonlinearities and interactions, were more appropriate for analyzing yield controls than traditional linear models. The results of this study indicate that adjustments in management can significantly improve wheat production in the Yaqui Valley but that the relevant controls change from year to year.

Surface Application of Lime for Crop Grain Production Under a No-Till System

Abstract: The effectiveness of surface application of lime to soils under a no-till (NT) system, particularly with regard to subsoil acidity, is uncertain, and long-term data is needed to determine optimum surface liming rates in this cropping system A field experiment was performed in the period from 1993 through 2003 in Parana State, Brazil, on a loamy, kaolinitic, thermic Typic Hapludox to evaluate the extent of the downward movement of surface-applied lime in a NT system, and the effect on grain yields under crop rotation The treatments consisted of dolomitic limestone at the rates of 0,2,4, and 6 t ha -1 , calculated to raise the base saturation in the topsoil (0-20 cm) to 50, 70, and 90% Surface-applied lime under NT was effective in alleviating soil acidity below the point of placement, and increased the cumulative grain yield of the crops The effects of surface liming on all three acidity-related variables (pH, Al, and basic cations) were significant at 0- to 5- and 5- to 10-cm depths from 1 yr onward, and also at the 10- to 20-cm depth from 25 yr onward, remaining consistent for a period of up to 10 yr after liming The maximum economic yield was obtained at 4 t ha -1 of limestone, showing that the lime rate estimated by the soil base saturation method at 70% in the 0- to 20-cm depth was appropriate for surface liming recommendation in a NT system

Forage Mixture Productivity and Botanical Composition in Pastures Grazed by Dairy Cattle

Abstract: Some producers believe that planting pastures to several forage species benefits sustainability of grazing systems. We conducted a grazing study to determine if forage species diversity in pastures affects herbage productivity and weed invasion. One-hectare pastures were planted to four mixtures in August 2001 and then grazed with lactating dairy cattle during 2002 and 2003. The mixtures were two species [orchardgrass (Dactylis glomerata L.) and white clover (Trifolium repens L.)], three species [orchardgrass, white clover, and chicory (Cichorium intybus L.)], six species {orchardgrass, tall fescue (Festuca arundinacea Schreb.), perennial ryegrass (Lolium perenne L.), red clover (Trifolium pratense L.), birdsfoot trefoil (Lotus corniculatus L.), and chicory], and nine species [the six-species mixture plus white clover, alfalfa (Medicago saliva L.), and bluegrass (Poa pratensis L.)]. When rainfall was plentiful (2003), there were no differences in herbage yield among the mixtures; all averaged 9800 kg ha -1 dry matter. During 2002, which was dry, the two-species mixture produced less herbage than the other mixtures (4800 vs. 7600 kg ha -1 dry matter). The proportion of nonsown species in the sward was lower for the six- and nine-species mixtures than the two-and three-species mixtures, indicating less weed invasion for these complex mixtures. Red clover and chicory proportions decreased by 80% after 2 yr, and orchardgrass dominated in all pastures by May 2004. We conclude that planting a mixture of grasses, legumes, and chicory will benefit herbage production during dry years and will reduce weed invasion for a few years after planting under management similar to ours. Producers would have to reestablish the chicory and legume components relatively frequently to maintain these benefits.

Fate of nitrogen-15 in a long-term nitrogen rate study: II. Nitrogen uptake efficiency

Abstract: Increased fertilizer N uptake efficiency (FNUE) leads to more economical corn (Zea mays L.) production and lower environmental impact. Excessive N application reduces FNUE and may affect subsequent crop response through its influence on NO 3 -N carryover and the amount of readily mineralizable organic N in the soil. Our objective was to determine how prior fertilizer N application rate affects (i) grain yield and agronomic optimum N rate, (ii) contributions of fertilizer- and soil-derived N to N uptake, and (iii) FNUE. Labeled 15 NH 4 15 NO 3 was applied at 0, 67, 134, 201, or 268 kg N ha -1 to subplots within a continuous corn long-term N rate study. Estimates of FNUE were higher by the difference method (49-69%) than with the isotope ( 15 N) method (31-37%), and different trends were observed with each method as N application rate increased. The disparity between methods is consistent with a differential effect of long-term N application rate on mineralization-immobilization. Recovery of labeled N from the plant-soil system ranged from 71% at the 67 kg ha -1 N application rate to 64% at the 201 kg ha -1 application rate. Fertilizer N accounted for an increasing proportion of crop N uptake as the N rate was increased, but soil N uptake was always more extensive, accounting for 54 to 83% of total plant N. Crop uptake of labeled N during the second growing season after 15 N application ranged from 2.2 kg ha -1 with the lowest N rate to 7.8 kg ha -1 with the two highest rates.

Legume Green Fallow Effect on Soil Water Content at Wheat Planting and Wheat Yield

Abstract: and yields were compared with wheat yields from conventional till other studies wheat yields following the green fallow wheat–fallow. Generally there were no significant differences in available soil water at wheat planting due to legume type. Soil water at period have been decreased due to lower soil water wheat planting was reduced by 55 mm when legumes were terminated content at wheat planting (Zentner et al., 1996; Schlegel early and by 104 mm when legumes were terminated late, compared and Havlin, 1997) or due to N deficiency (Pikul et al., with soil water in fallowed plots that were conventionally tilled. Aver- 1997). Under the higher temperature, higher evaporaage wheat yield was linearly correlated with average available soil tive demand environmental conditions of the central water at wheat planting, with the relationship varying from year to Great Plains, the positive economic trade-off between year depending on evaporative demand and precipitation in April, water used by the legumes and their favorable rotation May, and June. The cost in water use by legumes and subsequent and N fixing effects have not been observed (Vigil and decrease in wheat yield may be too great to justify use of legumes as Nielsen, 1998). The objectives of this study were (i) to fallow cover crops in wheat–fallow systems in semiarid environments. determine the effect of legume termination date (using four legume species) on available soil water content at winter wheat planting and subsequent wheat yield in a

Yield Response of Corn to Crowding Stress

Abstract: Plants grown at noncompetitive densities (isolated plants) can be used to relate competitive pressure on yield and yield components at high plant densities. The main objective of this research was to quantify the sensitivity of grain yield and its components to manipulation of crowding stress in corn (Zea mays L.). The experiment was conducted in Deerfield, MA (1986, 1987, and 2000), and Shoush, Iran (1998 and 1999). Three single-ear corn hybrids were planted at six densities (0.25, 3, 4.5, 6, 9, and 12 plants m -2 ), the lowest density being considered an isolated density. The higher three densities (6, 9, and 12 plants m -2 ) were combined with three removal treatments, consisting of removal of alternate plants in rows at different stages of growth. Intensity of competition was quantified by comparing grain yield and its components of plants in these densities with those of isolated plants. The highest grain yield in all experimental sites was obtained from 9 plants m -2 and for total biomass yield between 9 and 12 plants m -2 . Kernel yield per plant decreased linearly in all hybrids as plant density intensified. All yield components had a linear decline in response to increased competition pressure. The reduction in kernel yield was attributed most to the reduction in number of kernels per row. Removal treatments indicated that early competition during vegetative growth had no or little effect on final grain yield. Plant competition between the vegetative stage and anthesis had a large effect on grain yield reduction, which ranged from 8 to 21% in different hybrids and experimental sites. Increased assimilate supply through plant removal again confirmed that adjustments in grain yield occurred primarily through kernel number per row.

Corn Yield Response to Nitrogen Rate and Timing in Sandy Irrigated Soils

Abstract: yield response to N fertilizer is important in providing effective N management recommendations over a wide Efficient use of N fertilizer for corn (Zea mays L.) production range of soil–climate conditions, minimizing the potenis important for maximizing economic return and minimizing NO3

A multi-tactic approach to manage weed population dynamics in crop rotations

Abstract: L.) are now grown with winter wheat and fallow. Integrating crop diversity with other cultural tactics enabled No-till systems have enabled producers to change crop rotations in producers to effectively control weeds with 50% less the semiarid Central Great Plains. Previously, winter wheat (Triticum aestivum L.)–fallow was the prevalent rotation; now producers grow herbicide inputs compared with their initial experiences warm-season crops along with winter wheat and fallow. Initially, weed with no-till rotations (Anderson, 2003). The cultural management was difficult in no-till rotations. However, an ecological approach reduced weed community density in their fields, approach to weed management, which integrates knowledge of weed thus minimizing the need for herbicides to control weeds. population dynamics with cultural tactics and long-term planning, has Pedigo (1995) suggested that scientists develop conenabled producers to control weeds with 50% less herbicides. This ceptual models to guide development of multi-tactic article explains the cultural tactics and ecological reasoning that led programs. In this article, we explain the cultural tactics to this successful approach; our goal is to provide insight and ideas and ecological reasoning that led to this approach with for other scientists and producers to plan multi-tactic weed manageweed management in the Central Great Plains; this exment.The ecologicalapproach emphasizesthree goalsrelated toweed ample may provide insight and ideas for producers and population dynamics: enhancing natural loss of weed seeds in soil, reducing weed seedling establishment, and minimizing seed produc- scientists elsewhere to develop similar programs. Even tion by established plants. Cultural tactics used in this approach can though crop choices and cultural tactics may vary in be grouped into five categories: rotation design, crop sequencing, no- other regions, a systematic approach to integrating tactill, crop residue management, and competitive crop canopies. Success tics that disrupt weed population growth may lead to of the approach requires cultural tactics in each category. successful weed management that is less dependent on herbicides.

Efficiency of sulfuric acid, mined gypsum, and two gypsum by-products in soil crusting prevention and sodic soil reclamation

Abstract: Sulfuric acid and gypsum-like by-products are potentially effective amendments in preventing soil crusting and reclaiming calcareous sodic soils. However, their relative efficiencies at chemically equivalent rates are not well documented. We evaluated the efficiency of four amendments (sulfuric add, mined-gypsum, and the by-products coal-gypsum and lacto-gypsum) in crusting prevention of two calcareous nonsodic and sodic soils and in sodic soil reclamation. Treatments for crust prevention consisted of surface-applied amendments at equivalent rates of 5 Mg pure-gypsum ha -1 . Treatments for sodic soil reclamation consisted of surface-applied add and soil-incorporated gypsums at rates of 1 pure-gypsum requirement. The efficiency of these amendments was evaluated by comparing the final infiltration rates (FIR) of the amended vs. the nonamended soils measured in disturbed-soil columns pounded with low-salinity irrigation water. Electrical conductivity (EC) and Na in the leachates of the sodic soil were measured. In the crusting prevention experiment, FIRs (mm h -1 ) of the nonsodic soil were 21 (nonamended), 33 to 35 (gypsum materials), and 53 (sulfuric acid), whereas those for the sodic soil were 0 (nonamended), 9 (lacto-gypsum), 15 to 17 (coal- and minedgypsum), and 21 (sulfuric acid). In the sodic-soil reclamation experiment, FIRs were 0 (nonamended), 8 to 9 (gypsum-materials), and 17 (sulfuric add) mm h -1 . All amendments were effective in crusting prevention and soil reclamation, but sulfuric acid was the most efficient due to the fastest EC and Na reductions in the leachates. The three gypsum-materials were equally effective in the reclamation process and in the nonsodic soil crusting-prevention, whereas lacto-gypsum was less efficient in the sodic-soil crusting-prevention.

Management, topographical, and weather effects on spatial variability of crop grain yields

Abstract: The quantitative characterization of spatiotemporal variability in crop grain yields is an important component for successful precision-agriculture applications. The objective of this study was to analyze and quantify effects of management practices, topographical features, and weather conditions on spatial variability of crop yields. A one-factor randomized complete block design experiment with six replications was established at the Long Term Ecological Research site in southwest Michigan in 1988. The treatments used in this study were two treatments with conventional chemical inputs (chisel plow and no-till) and two organic-based chisel-plowed treatments with a winter leguminous cover crop (low chemical input and zero chemical input). The data consisted of corn (Zea mays L.)-soybean [Glycine max (L.) Merr.]-wheat (Triticum aestivum L.) yields collected via combine monitors from 1996 to 2001. We observed that stressful conditions, regardless of the stress origin, were associated with increase in the overall yield variability (coefficient of variation) as well as the small-scale yield variability (variogram values at short lag distances and variogram slopes near the origin) with yields probably being more sensitive to the small-scale variations in growth conditions due to soil and microtopographical differences. Coefficients of variation were as high as 45% in years with low precipitation and as low as 14% in years with above-average precipitation. During the years with low precipitation, both the coefficients of variation and the small-scale variability were often significantly higher in the zero chemical input treatment than in the treatments that received fertilizer inputs. The coefficients of variation and the small-scale variability parameters also tended to be higher in corn stressed by antagonism from previous wheat crop in the no-till treatment.

Simulating Planting Date Effects on Corn Production Using RZWQM and CERES‐Maize Models

Abstract: Corn (Zea mays L.) production in northeastern Colorado is constrained by a frost-free period averaging 11 May to 27 September. For optimization of yield, planting at the appropriate time to fit the hybrid maturity length and growing season is critical. Crop models could be used to determine optimum planting windows for a locality. We calibrated the plant parameters of the Root Zone Water Quality Model (RZWQM) and genetic coefficients for the CERES-Maize model and validated their performance against experimental data of three corn hybrids varying in days to maturity, planted on three planting dates in 2 yr at Akron, CO, under irrigation. Both models could be calibrated to predict leaf area index, soil water content, crop water use, and yield with similar levels of accuracy. Both models simulated the observed decline in yield with delayed planting date, but CERES-Maize simulated the yield from the latest planting date much more accurately for all three hybrids than did RZWQM (13% underpredicted by CERES-Maize; 50% overpredicted by RZWQM). Using the long-term Akron weather record, the latest planting dates for the short-, mid-, and long-season hybrids to have a 50% chance of achieving a break-even yield under irrigation were 13 May, 20 May, and 6 May, respectively. Long-term simulations also revealed that the longer maturity length hybrids lose yield faster than short maturity length hybrids with planting delay. The information generated by either RZWQM or CERES-Maize can be useful for making both planting and replanting decisions for corn hybrids of varying maturity length in northeastern Colorado.

Long-Term Evaluation of Poultry Litter as a Source of Nitrogen for Cotton and Corn

Abstract: Land application of poultry broiler litter (BL) in agricultural production is a widely used practice. However, cotton (Gossypium hirsutum L.) growers in poultry-producing regions of the southern USA have been reluctant touse BL as a crop nutrient source. Field experiments were conducted for 13 yr to study the effect of BL application to cotton and corn (Zea mays L.) under conventional and conservation tillage systems. Nitrogen rates from 0 to 269 kg ha - 1 were applied annually at two locations to compare the effect of BL and ammonium nitrate (AN) as N sources. The relationship between the total N rates (N) applied and the relative N availability (y) based on the crop yield by application of BL and AN is described by linear equation: y = 71.58 + 0.15N (r = 0.66). In most years, there were no differences in relative yields from total N applied as BL or AN. The amplitude of yield increase based on N source varied with rainfall during the growing season. The residual effect of BL in the second year after application resulted in 30 to 50% of the cotton lint yield and 25 to 65% of the corn grain yield that resulted from a standard N fertilization rate. General observations suggest that N availability from BL is similar whether surface-applied as in conservation tillage systems or incorporated as in conventionally tilled systems.

Selection of Optimum Reflectance Ratios for Estimating Leaf Nitrogen and Chlorophyll Concentrations of Field-Grown Cotton

Abstract: Leaf N and chlorophyll (Chl) concentrations of cotton (Gossypium hirsutum L.) are important indicators of plant N status. Laboratory determinations of plant tissue N are time consuming and costly. Measurements of leaf reflectance may provide a rapid and accurate means of estimating leaf N and Chl. Studies were conducted to determine the relationships between leaf hyperspectral reflectance (400-2500 nm) and Chl or N concentration in field-grown cotton. One study consisted of four N rates of 0, 56, 112, and 168 kg N ha -1 , and another study consisted of four mepiquat chloride (MC) rates of 0, 0.59, 1.17, and 2.34 L MC ha -1 . Chlorophyll and N concentrations and reflectance of uppermost, fully expanded mainstem leaves were measured throughout the growing seasons. Reflectance at 556 and 710 nm increased significantly as N fertilizer rate decreased. Averaged across years and sampling dates, the percentage increase in reflectance at these two wavelengths was 8, 10, and 19% greater in the 112, 56, and 0 kg N ha -1 treatments, respectively, compared with the 168 kg N ha -1 treatment. The effect of MC on leaf reflectance was more complex than the N effect. In both the N and MC studies, a linear relationship was found between leaf N and a simple ratio of leaf reflectance at 517 and 413 nm (R 517 /R 413 ) (r 2 = 0.65-0.78***). Leaf Chl concentration was associated closely with reflectance ratios of either R 708 /R 915 or R 551 /R 915 (r 2 = 0.67-0.76***). Our results suggest leaf reflectance can be used for real-time monitoring of cotton plant N status and N fertilizer management in the field.

Predicting rice yield using canopy reflectance measured at booting stage

Abstract: Abilities to estimate rice (Oryza sativa L.) yields within fields from remote sensing images is not only fundamental to applications of precision agriculture, but can also be very useful to food provisions management. Major objectives of this study were to identify spectral characteristics associated with rice yield and to establish their quantitative relationships. Field experiments were conducted at Shi-Ko experimental farm of TARI's Chiayi Station during 1999-2001. Rice cultivar Tainung 67, the major cultivar grown in Taiwan, was used in the study. Various levels of rice yield were obtained via N application treatments. Canopy reflectance spectra were measured during entire growth period, and dynamic changes of characteristic spectrum were analyzed. Relationships among rice yields and characteristic spectrum were studied to establish yield estimation models suitable for remote sensing purposes. Spectrum analysis indicated that the changes of canopy reflectance spectrum were least during booting stages. Therefore, the canopy reflectance spectra during this period were selected for model development. Two multiple regression models, constituting of band ratios (NIK/RED and NIR/GRN), were then constructed to estimate rice yields for first and second crops separately. Results of the validation experiments indicated that the derived regression equations successfully predicted rice yield using canopy reflectance measured at booting stage unless other severe stresses occurred afterward.

Carbon Storage in Soils of the North American Great Plains: Effect of Cropping Frequency

Abstract: Summer fallow (fallow) is still widely used on the North American Great Plains to replenish soil moisture between crops Our objective was to examine how fallowing affects soil organic carbon (SOC) in various agronomic and climate settings by reviewing long-term studies in the midwestern USA (five sites) and the Canadian prairies (17 sites) In most soils, SOC increased with cropping frequency though not usually in a linear fashion In the Canadian studies, SOC response to tillage and cropping frequency varied with climate-in semiarid conditions, SOC gains under no-till were about 250 kg ha - 1 yr - 1 greater than for tilled systems regardless of cropping frequency; in subhumid environments, the advantage was about 50 kg ha - 1 yr - 1 for rotations with fallow but 250 kg ha - 1 yr - 1 with continuous cropping Specific crops also influenced SOC: Replacing wheat (Triticum aestivum L) with lentil (Lens culinaris Medikus) had little effect; replacing wheat with lower-yielding flax (Linum usitatismum L) reduced SOC gains; and replacing wheat with erosion-preventing fall rye (Secale cereale L) increased SOC gains In unfertilized systems, cropping frequency did not affect SOC gains, but in fertilized systems, SOC gains often increased with cropping frequency In a Colorado study (three sites each with three slope positions), SOC gains increased with cropping frequency, but the response tended to be highest at the lowest potential evaporation site (where residue C inputs were greatest) and least in the toeslope positions (despite their high residue C inputs) The Century and the Campbell et al SOC models satisfactorily simulated the relative responses of SOC although they underestimated gains by about one-third

Fate of Nitrogen-15 in a Long-Term Nitrogen Rate Study: I. Interactions with Soil Nitrogen

Abstract: A better understanding of how N management practices affect transformations and movement of fertilizer N may lead to more efficient N management. The objectives of this work were to determine how long-term N fertilizer history in a continuous corn (Zea mays L.) production system affects (i) movement of fertilizer N through the soil profile and (ii) cycling of fertilizer N between available and nonavailable soil forms. Nitrogen-15-labeled ammonium nitrate ( 15 NH 4 15 NO 3 ) was applied at 0, 67, 134, 201, or 268 kg N ha -1 to subplots of long-term N rate plots. Twenty to 55% of labeled N was converted into either organic or clay-fixed forms during the first growing season, with the percentage decreasing with increasing N application rate. Significantly more N was released from nonavailable forms in plots where the historical N application rate had exceeded the long-term optimum (186 kg ha -1 ) than in plots that received lower rates. Little fertilizer-derived N leached from the profile during the first growing season, but losses did occur during the off-season and subsequent growing season when N application rate was higher than the optimum. It was concluded that a history of excessive N application may decrease response of subsequent crops to fertilizer N due to greater release from nonavailable N forms, most likely as a result of increased mineralization of crop residues and recently formed soil organic N.

Integrating Cotton and Beef Production to Reduce Water Withdrawal from the Ogallala Aquifer in the Southern High Plains

Abstract: Agriculture in the Texas High Plains depends heavily on irrigation with water withdrawn from the Ogallala aquifer at nonsustainable rates Our hypothesis was that integrating crop and livestock systems would reduce irrigation water use, maintain profitability, and diversify income compared with a cotton (Gossypium hirsutum L) monoculture Thus, from 1998 to 2002, two large-scale systems, with three replications in a randomized block design, compared water use, productivity, and economics of (i) a cotton (var 'Paymaster 2326RR') monoculture with terminated wheat (Triticum aestivum L) and (ii) an integrated three-paddock system that included cotton in a two-paddock rotation with grazed wheat and rye (Secale cereale L) and the perennial 'WW-B Dahl' old world bluestem [Bothriochloa bladhii (Retz) ST Blake] for grazing and seed production All paddocks were irrigated by subsurface drip Angus crossbred beef steers (Bos taurus L; initial body weight = 249 kg; standard deviation = 26 kg) grazed from January to mid-July During the 4 yr of this experiment following the establishment year, cotton lint yield was 1036 and 1062 kg ha - 1 for the cotton monoculture and the integrated system, respectively Bluestem seed yield averaged 24 kg pure live seed ha - 1 Steers gained 153 kg on pasture and 082 kg d - 1 Per hectare, the integrated system used 23% less (P < 0001) irrigation water, 40% less N fertilizer, and fewer other chemical inputs than the cotton monoculture Profitability was about 90% greater for the integrated system at described conditions Integrated production systems that are less dependent on irrigation and chemical inputs appear possible while improving profitability