Agronomy Journal

Teare, I. D.; Wright, D. L.; Stanley, R. L.; Kidd, B. T.

doi: 10.2134/agronj1987.00021962007900010001xpmid: N/A

The fertilization of slash pine trees (Pinus eliotti Engelm), a practice initiated in the sixties, stimulates bahiagrass (Paspalum notatum Flügge) production, providing under‐canopy forage for the beef cattle industry of the Southeast on sandy, acid soils. Little research has been conducted to determine the production potential of limed and N fertilized bahiagrass growing under pine. The objectives of this research were to measure bahiagrass forage production under slash pine, comparing lime (2.24 Mg ha−1) vs. no lime, four N rates (28, 56, 112, 224, kg ha−1), and to observe changes in extractable soil P, K, and pH on a Norfolk sandy loam (fine‐loamy, siliceous, thermic Typic Paleudult). During the 4yr period, application of 2.24 Mg ha−1 lime empirically decreased bahiagrass forage yield under pines when averaged across N levels. Liming at 2.24 Mg ha−1 yr−1 for 4 yr did change the soil pH from 5.0 to 6.1. Nitrogen rates did not affect bahiagrass forage production the first year, but without lime, we found a quadratic response to N rates each year thereafter. The highest yields of bahiagrass forage with lime were obtained with 56 kg ha−1 N. Economic analysis shows the greatest net return ($441 over 4 yr) for no lime at 112 kg ha−1 N and with lime ($211) at 56 kg ha−1 N.

Brede, A. D.

doi: 10.2134/agronj1987.00021962007900010002xpmid: N/A

Field research with turfgrass seedlings is frequently complicated by weather disruptions and sampling error. A technique was developed for affixing turf seeds to a seedbed in the field for the purpose of monitoring field survival and growth of seedlings over time. Isolated plots of turfgrass seeds, 25 mm in diam and spaced 75 mm apart on a seedbed, were held in place with a liquid latex‐based mulch and a non‐woven fabric mulch. Seed displacement from rainwashing was held below 0.1% with this technique. The latex/fabric mulches had the same effect on seedling growth as do conventional mulches of straw or wood fiber; therefore, use of the latex/fabric mulches in this technique did not seem to constitute a serious deviation from standard planting practices. Results from field evaluations revealed that field survival (percent germination) was accurately assessed using this technique without the added variance associated with subsampling of solid stands. Field survival of perennial ryegrass (Lolium perenne L.) seedlings sown at 59 200 seeds m−2 could be measured with 9% variability (CV), vs. 35 to 51% variability with traditional sampling‐probe methods. Values of field survival obtained using isolated plots corresponded closely with values found in solid stands but with lesser variability. Plant growth parameters (leaves, shoots, roots) in isolated plots and solid stands diverged over time; interspecific competition occurred sooner in solid stands than in isolated plots. Care should be taken when extrapolating seedling growth results found using this technique to solid stand conditions since the seedlings are essentially space planted.

Russo, David

doi: 10.2134/agronj1987.00021962007900010003xpmid: N/A

Evaluation of the possibility of utilizing marginal soils and saline waters for agricultural production is essential for the development of arid zones. The effect of irrigation water quality (salinity) and quantity on the yield of lettuce (Lactuca saliva var. ‘Iceberg’) was studied in a gypsiferous desert soil (Typic Torrifluvent). Irrigation water volume (Q) ranging from 0.37 to 1.3, 0.6 to 1.6, and 0.7 to 2.4 times the Class A pan evaporation (Eo) for the irrigation water salinities of Ciw = 1.7, 3.1, and 4.7 dS/m, respectively, were applied via trickle irrigation. Root zone soil water pressure potential and salinity were monitored and lettuce yield was measured. Seasonal average soil water content (θ̅) was affected by irrigation water volume but not by quality (salinity) whereas seasonal average soil water salinity (E̅C̅) and lettuce yield (Y) were affected by both quality and quantity of the irrigation water. For the different ranges of Q associated with the different irrigation waters, θ̅ was increased by 30, 44, and 94%, EC was decreased by 20, 21, and 18%, and Y was increased by 120, 71, and 55% for Ciw = 1.7, 3.1, and 4.7 dS/m, respectively. Curvelinear salt tolerance functions were found to be dependent on the volume of irrigation water, approaching a piecewise linear function when relatively large volumes of irrigation water (Q/Eo > 1) were applied. The increase in irrigation volume compensated only in part for the adverse effect of the irrigation water salinity. Maximum yields obtained using the more saline waters are 6.5 and 20.7% smaller for Ciw = 3.1 and 4.7 dS/m, respectively, relative to yield obtained using Ciw =1.7 dS/m.

Hiebsch, C. K.; McCollum, R. E.

doi: 10.2134/agronj1987.00021962007900010004xpmid: N/A

Production systems involving interplanted food crops are widespread in tropical latitudes, and interest in quantifying the productive potential of intercrops is high. Published data often suggest a sizable gain in land‐use efficiency by growing such crops in mixtures. Our thesis is that many of the large intercrop advantages reported in the literature are misleading because the conceptual basis on which the monoculture‐vs.‐intercrop comparisons were made is incomplete. In this paper, we review the various methods for estimating intercrop productivity, propose a concept which we believe will remove the principal limitation in conventional methodology, and test the new concept with intercrop data from the literature. The land equivalency ratio (LER) is the most‐used convention for intercrop‐vs.‐monoculture comparisons, but LER is frequently inappropriate because cropping‐system duration, i.e., time, is not included in its calculation. Duration of land occupancy by an intercrop is often longer than production‐cycle duration for one or more of the interplanted species. We propose an area‐×‐time equivalency ratio (ATER) and suggest that it will correct this conceptual inadequacy in LER. When published intercrop data were reevaluated via the ATER concept, large land‐use advantages ascribed to growing food crops in mixtures disappeared. We conclude that most crop mixtures utilize land area and time (area·time) at about the same efficiency as pure stands of the mixture's components.

Webb, D. M.; Smith, C. W.; Schulz‐Schaeffer, J.

doi: 10.2134/agronj1987.00021962007900010005xpmid: N/A

Seedling emergence studies are normally conducted in growth chambers, greenhouses, or field plots and require much space, equipment, and time when several factors are considered. Amaranth (Amaranthus spp.) is a new crop in the United States that often exhibits inadequate field emergence because of environmental constraints. Two seedlots, one white seeded and one black seeded, from the same population of Amaranthus hypochondriacus L. were assessed for emergence index and percentage emergence in a peat‐sand medium over a range of temperatures and seeding depths using a modified thermogradient plate. Seed color produced no difference in emergence, but significant differences in emergence were caused by temperature, seeding depth, and temperature × depth interaction. A predictive response surface shows expected amaranth seedling emergence index at temperatures between 15 and 42°C and seeding depths between 13 and 51 mm. Highest amaranth emergence index and percentage emergence on the thermogradient plate occurred from the 13‐mm seeding depth and at temperatures between 24 and 34°C; these data suggest field emergence may be satisfactory with soil temperatures between 18.5 and 24°C.

Romo, James T.; Haferkamp, Marshall R.

doi: 10.2134/agronj1987.00021962007900010006xpmid: N/A

Forage kochia [Kochia prostrata (L.) Schrad.] may be useful for revegetating salt affected soils. This study was designed to quantify the effects of temperature, water stress, and specific ions on the germination of ‘Immigrant’ forage kochia. Fruits and seeds were germinated at 10, 20 and 30°C in solutions of polyethylene glycol (PEG) with osmotic potentials ranging from −0.52 to −2.32 MPa. Seeds were also germinated at 20°C in PEG solutions containing 0 to 53 640 µmol L−1 potassium chloride (KCl‐PEG) and 0 to 68 480 µmol L−1 sodium chloride (NaCl‐PEG) with osmotic potentials ranging from −0.3 to −2.2 MPa. Germination was reduced by declining osmotic potentials. Total germination was highest at 20°C and lower at 10 and 30°C. Germination in NaCl‐PEG and KCl‐PEG solutions was primarily reduced by low osmotic potentials; percent germination was not affected by increasing NaCl concentrations but was reduced by increasing KCl concentrations. Number of days to 50% final germination was similar in both salts, increasing as osmotic potential declined and salt concentration increased. Forage kochia appears moderately tolerant of NaCl and KCl during germination and growth and may be well suited for revegetating salt affected soils in the Intermountain Region. Fruits are recommended for planting because abnormal germination was less than with seeds. Forage kochia should be sown prior to periods when soil temperatures are in the 10 to 20°C range, and cultural practices that extend the period of high soil osmotic potentials should be used to maximize seed germination.

Kohel, R. J.; Benedict, C. R.

doi: 10.2134/agronj1987.00021962007900010007xpmid: N/A

Field and greenhouse experiments were conducted on cotton (Gossypium hirsutum L.) lines with differing maturities to determine what factors of plant growth contributed to early crop maturity and how these factors were related. Earliness was measured in terms of flowering, boll setting, length of boll maturation, and crop maturity. Additional measurements included plant growth and dry weight partitioning, productivity, and agronomic performance. Plant maturity was determined by time of flowering and length of boll maturation. Lines with the earliest crop maturities produced the lowest yields per plant. Performance of individual early maturing lines, such as 6 M, with improved agronomic properties, demonstrated the ability to increase early crop maturity with improved yield.

Levin, A.; Beegle, D. B.; Fox, R. H.

doi: 10.2134/agronj1987.00021962007900010008xpmid: N/A

It has been shown that there are significant differences in the potential rate of mineralization and nitrification between conventional and no‐till soils. However, the practical effect of this difference on the availability of residual N from a legume and yield of a succeeding corn crop is unclear. Two field experiments in which corn (Zea mays L.) followed alfalfa (Medicago sativa L.) were conducted on a Hagerstown silt loam (fine, mixed, mesic Typic Hapludult) and on a Gilpin channery silt loam (fine‐loamy, mixed, mesic Typic Hapludult) to determine the effect of no‐tillage (NT) and conventional tillage (CT) methods on residual N availability from the legume as measured by yield and N uptake of the succeeding corn crop. Five rates of N (0, 45, 90, 135, and 180 kg ha−1) as ammonium nitrate were surface applied as either at‐planting or sidedress applications. The mean soil N‐supplying capability was 126 kg N ha−1 at both sites. There was no interaction between tillage method and N response, indicating that the fertilizer N recommendations for first‐year corn following alfalfa should be similar for NT and CT methods. Optimum economic grain yields for first‐year corn resulted with the application of 83 and 88 kg N ha−1 for the NT and CT treatments, respectively, at one site and with no added N at a second site, confirming this conclusion. The experiment was repeated for the second year at one site and the results for the second year also indicated that there was no difference in N fertilizer response due to tillage and no interaction between tillage and N response. Again this would indicate that N recommendations should be similar for the two tillage systems. There was no yield response to time of N application.

Turner, D. L.; Dickens, R.

doi: 10.2134/agronj1987.00021962007900010009xpmid: N/A

Centipedegrass [Eremochloa ophiuroides (Munro) Hack.] sod has become more in demand over the past decade, leading producers to attempt to speed production. An increase in the use of the herbicide atrazine [6‐chloro‐N‐ethyl‐N'‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] for weed control has been one result. Numerous sod producers in the Southeast have experienced difficulty harvesting sod due to inadequate tensile strength. The object of this study was to determine the effects of atrazine on the tensile strength of centipedegrass sod. The experiment was conducted during 1982, 1983, and 1984 at Auburn, AL, on a Dothan sandy loam (Plinthic Paleudult) and during 1982 and 1983 at Tuskegee, AL, on a Gilead sandy loam (Aquic Hapludult) and a Leaf silt loam (Typic Albaquult), respectively. Atrazine was applied to centipedegrass at 0.6, 1.1, and 2.2 kg ha−1 rates at 2‐ and 4‐week intervals during the growing season. Visual injury ratings were taken in July, September, and May, and sod tensile strength measurements were taken in September and May following applications. Visual observations indicated that injury was increased as atrazine rates and application frequencies increased. Less Injury occurred in 1983 at both locations. Visual injury ratings were not consistent with sod tensile strength measurements. Measurements of sod tensile strength revealed that increasing rates of atrazine reduced the tensile strength in a linear fashion. Injury was greater with the 2‐week application interval. Reduction of tensile strength was more evident with sod harvested in September than in May at both locations. Sod tensile strength of untreated centipedegrass was higher during September than during the following May and at the Auburn location.

Reddy, V. R.; Baker, D. N.; Whisler, F. D.; Fye, R. E.

doi: 10.2134/agronj1987.00021962007900010010xpmid: N/A

Cotton (Gossypium hirsutum L.) yields have declined since 1965 despite improvements in technology and introductions of higher yielding cultivars. Cotton scientists have been unable to identify exact causes of the yield decline. One suggested cause is the increased use of herbicides and their toxic effects on root growth in the herbicide incorporated zone. In this study, the computerized crop simulation model, GOSSYM, was used to predict cotton performance under several levels of herbicide‐induced root reduction under various environmental conditions in a Leeper clay loam soil (fine, montmorillonitic, nonacid, thermic Vertic Haplaquept). The model predicted a small increase in yield when root reduction was moderate and at shallow depths. However, when the depth of root reduction increased to 200 mm or the percentage of root reduction increased, there was a predicted decrease of up to 40% in cotton lint yield. This decrease in lint yield was much larger when decreased root length was combined with reduced soil water permeability in remaining roots. Predicted yield was also reduced under unfavorable weather conditions. With increase in the depth of root reduction or increase in the percentage of root reduction and with permeability reduction there was a decrease in the root growth throughout the season. Increased N and water shortages were apparent with increase in the depth or level of root reduction. It was concluded that improper application of herbicides was one of the contributing factors for the cotton yield decline.