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doi: 10.2134/agronj1994.00021962008600030002xpmid: N/A
Arbuscular mycorrhizal fungi (AMF), ubiquitous symbiotic fungi colonizing plant roots, can contribute to plant growth by improving nutrient uptake and stress tolerance. The influence of management practices and crop species on AMF spore populations and percent root colonization was examined during conversion from conventional to low‐input and low‐input to conventional management systems in 2‐yr crop rotations planted to alternating corn (Zea mays L.)‐soybean [Glycine max (L.) Merr.] sequences established in two adjacent areas with different management histories. During the previous 25 yr, the low‐input area had received no fertilizer or herbicide inputs, while the conventionally managed area had received recommended fertilizer and herbicide inputs. No input (NI), organic input (OI), minimum input (MI), and conventional input (CI) management systems were established within each crop sequence. Weeds were the dominant vegetation in both years in the low‐input area. Average AMF spore population in this area was 292 spores g−1 soil. In the conventionally managed area, only crop plants were present during the first year, while small weed populations had developed by the end of the second year in NI and OI. Average AMF spore population in the conventionally managed area was 175 spores g−1 soil. Average AMF colonization percentage in the low‐input area was 27.5%, while in the conventionally managed area it was 24.5%. AMF colonization percentages were not correlated with AMF spore populations and did not appear to be influenced by the management systems established within each area. Management systems appeared to influence AMF spore populations by their effect on weed populations.
Larson, E. J.; Vanderlip, R. L.
doi: 10.2134/agronj1994.00021962008600030003xpmid: N/A
Nonuniform stand reductions caused by poor emergence, insect damage, or other factors, occur frequently in grain sorghum [Sorghum bicolor (L.) Moench] fields. This research was conducted to determine the effect of within‐row skip patterns on grain yield and yield component compensation, particularly for hybrids differing in tillering ability. Dryland field studies were conducted at Manhattan (Reading silt loam, fine‐silty, mixed, mesic Typic Argiudoll) and St. John (Naron fine sandy loam, fine‐loamy, mixed, thermic Udic Argiustoll), KS, during 1988 and 1989. Two medium‐maturity hybrids, DeKalb DK‐46 and Pioneer 8500, were selected based on low and high tillering ability. Plots were three rows, with the middle row containing a within‐row skip pattern. Results were analyzed separately by skip row, adjacent row, and average for the three rows. Skip lengths within a 7.6‐m row were 0.9 m, 0.9 m repeated three times, and 2.7 m within the skip row, and the 0.9 m × 3 pattern in all three rows. Yield of the skip row was reduced by every configuration bordered by control stand adjacent rows. Yield compensation from adjacent rows and within the skip row compensated for reduced stands, except for a 2.7−m skip resulting in 5.1% yield reduction, 64% uniformly spaced stand in all three rows with 6.9% yield reduction, and three 0.9 m within‐row skips in all three rows with 10.9% yield reduction. Compensation was primarily in number of heads per plant and seeds per head. Difference in hybrid tillering response did not influence grain yield. Thus, yield reduction is likely only where skips result in severe plant spacing nonuniformity.
doi: 10.2134/agronj1994.00021962008600030004xpmid: N/A
Rice (Oryza sativa L.) ratooning is commonly practiced in the Everglades Agricultural Area of southern Florida, yet optimum length of the drained period between main and ratoon crops has not been determined. Research was conducted to determine the effect of length of drain period at main‐crop harvest on ratoon rice productivity on an Everglades Histosol. Our research was conducted in 250‐L (0.95 m height, 0.58 m i.d.) custom‐made water control lysimeters filled with a Pahokee muck soil (euic, hyperthermic Lithic Medisaprist). Ratoon reflood timing treatments were 0, 5, 15, 25, 35, and 45 d drained beginning at maincrop maturity. Ratoon‐crop grain yield exhibited a significant quadratic response to length of drain period with maximum grain yield produced at 28 d drained. Ratoon panicle number was not affected by reflood timing, but quadratic responses to length of drain period were observed for grain number and 1000‐grain weight. We propose that the resultant effect of reftood timing on ratoon grain yield was the combined responses to increasing mineral N supply and increasing water stress associated with delayed reftooding. For drained durations =28 d, the beneficial effects of increased mineral N supply resulting from organic matter oxidation resulted in a net increase in ratoon‐crop yield. Conversely, for drained periods >28 d, the detrimental impact of prolonged water stress dominated the response to reflood timing and ratoon rice yields declined.
Kludze, H. K.; DeLaune, R. D.; Patrick, W. H.
doi: 10.2134/agronj1994.00021962008600030005xpmid: N/A
Although not easily measured measured, oxygen release from rice (Oryza sativa L.) roots determines the plant's ability to survive reducing conditions. Our main objective was to test titanium‐citrate complex for its potential to quantify dissolved O2 concentrations in solutions bathing the whole root system of container‐grown rice cultivars. Influences of aeration status on root aerenchyma formation and radial oxygen loss from roots were also evaluated. Seven rice cultivars were grown in sand culture fertilized with nutrient solution under well drained and hypoxic conditions. Oxygen concentration was measured colorimetrically 6 h after placing plant roots in the Ti3+ ‐citrate solution. Plants were harvested for root porosity and radial oxygen loss estimates at 14 and 35 d after transplanting. Estimates of radial oxygen loss with the Ti3+‐citrate technique were comparable to those obtained with a polarographic oxygen electrode. Both radial oxygen loss and root porosity were enhanced by hypoxia. Rapid formation of aerenchyma at early growth stages coupled with correspondingly high O2 leakage from roots may explain why some rice cultivars cope with the adverse effects of anaerobiosis better than other cultivars.
Miller, Richard F.; Svejcar, Tony J.; Rose, Jeffrey A.; McInnis, Michael L.
doi: 10.2134/agronj1994.00021962008600030006xpmid: N/A
Attempts to control the noxious weed heart‐podded hoary cress [Cardaria draba (L.) Desv.] in the Pacific Northwest have been relatively ineffective, and this species has expanded its distribution from irrigated hayland onto adjacent semiarid rangelands. The objective of this study was to define the seasonal pattern of development and biological activity of heart‐podded hoary cress growing on semiarid rangeland. The study was conducted in the field over a 2‐yr period on a terrace site that has deep Cumulic Haploxeroll soil and an adjacent upland site that has a shallow Lithic Argixeroll soil. Soil water content, phenology, xylem pressure potential and leaf conductance were measured at both sites. Aboveand belowground biomass and spring C allocation pattern, determined by labeling plants with 13C, were measured at the terrace location. Regardless of location, no heart‐podded hoary cress seedlings were found; all shoots developed from rhizome buds. The majority (76%) of heartpodded hoary cress biomass was located belowground. Although drought occurred earlier on the upland than the terrace site, phenology was similar on the two sites. Carbon was translocated to belowground tissues within 1 h of labeling and reached peak accumulation within 24 h. The greatest 13C enrichment of roots and rhizomes occurred during the flowering stage. The peak in belowground C allocation occurred at a stage when leaf conductance was declining rapidly. The short period of maximum C allocation to belowground tissue, the large proportion of belowground tissue, and the wide variation of phenology among plants at a given time may account for the difficulty in chemically controlling this species.
doi: 10.2134/agronj1994.00021962008600030007xpmid: N/A
Cotton (Gossypium hirsutum L.) is sometimes grown on soils with low B concentration. However, most of the literature regarding the effects of supplemental B on cotton was obtained from obsolete, low‐yielding genotypes rather than modern, high‐yielding genotypes. Therefore, the objective of this study was to determine the effects of soil‐ and foliarapplied B on leaf blade B concentration, boll retention, and lint yield of modern cotton genotypes. In 1991, three genotypes (DES 119, DES 24‐8 ne normal leaf, and DES 24‐8 ne okra leaf) and in 1992, two genotypes (Deltapine 20 and Deltapine 5415) of cotton were grown in the field on a Beulah fine sandy loam (coarse‐loamy, mixed, thermic Typic Dystrochrepts) having 0.11 mg kg−1 hot water extractable B concentration. Treatments included preplant soil and foliar (first flower to end of bloom) B (78% Na2B8O13·4H2O, 20% Na2B4O7·5H2O) applications for seasonal totals of 0, 0.89, or 1.78 (1992 only) kg B ha−1. The lowest rate of foliar‐applied B increased leaf blade B concentration from 25 to 70 mg kg−1 in 1991 and from 54 to 108 mg kg−1 in 1992. In 1992, the highest rate of foliar B applications resulted in a leaf blade concentration of 154 mg B kg−1. Soil‐applied B did not alter leaf blade B concentration in 1991, but slightly increased leaf blade B concentration in 1992 from 54 to 71 mg kg−1. Soil B concentrations were higher during the midseason than the preplant period, suggesting that preplant soil B analysis may not accurately foreshadow soil B supply during the season. Soil B or foliar B applications did not affect boll retention percentage, flower number, or lint yield in either year. Supplemental B did not affect boll distribution in 1991, but in 1992, foliar B applications increased the percentage of fruit on monopodial branches. In both years, supplemental B did not greatly affect fiber properties with the exception that supplemental B increased fiber micronaire reading of Deltapine 20 in 1992. The results suggest that modern cultivars may not always need supplemental B when soil B concentration is moderately low.
Karnezos, T. P.; Matches, A. G.; Brown, C. P.
doi: 10.2134/agronj1994.00021962008600030008xpmid: N/A
Lamb (Ovis aries) weight gains from wheatgrass‐sainfoin (Agropyron and Thinopyron spp.‐Onobrychis viciifolia Scop.) mixtures suggest that grazing sainfoin monocultures offers advantages over mixtures. Our objective was to determine levels of spring lamb production from irrigated ‘Renumex’ sainfoin, ‘Cimmaron’ alfalfa (Medicago sativa L.), ‘Luna’ pubescent wheatgrass [T. intermedium subsp. barbulatum (Schur) Barkw. & D.R. Dewey], and pubescent wheatgrass‐sainfoin pastures. Replicated pastures grown on a fine, mixed, thermic Torrertic Paleustoll were rotationally stocked (herbage dry matter [DM] allowance of 6.5% of body wt. d−1) by weaned Rambouillet ✕ Suffolk wether lambs for an average of 88 d in spring of 1991 and 1992. Across years, cumulative weight gain (CWG) ranged between 7.9 kg lamb−1 for wheatgrass and 16.4 kg lamb−1 for alfalfa. In 1991 (avg. 16.1 kg lamb−1) and 1992 (avg. 12.3 kg lamb−1) CWG for alfalfa and sainfoin was similar. Lamb production per hectare (PROD) was greatest for legumes (808 kg lamb ha‐1) and least for wheatgrass (533 kg lamb ha−1). Including sainfoin with wheatgrass increased PROD by 23% over wheatgrass, whereas sainfoin alone increased PROD by 25% over the mixture. Intake of sainfoin herbage (1.5 kg DM lamb‐unit‐1 d‐1) was 29% greater than of alfalfa, wheatgrass, or wheatgrass‐sainfoin (1.2 kg DM lamb‐unit−1 d−1, where 1 lamb‐unit is a 35‐kg lamb). Herbage crude protein concentrations (pregrazing) were highest for alfalfa (253 g kg−1) and lowest for wheatgrass (159 g kg−1). Sainfoin had the lowest organic matter digestibility (641 g kg−1), which did not reflect the high CWG or PROD obtained. Alfalfa or sainfoin offer greater opportunities for spring lamb production than wheatgrass or wheatgrass‐sainfoin pastures.
Smith, D. Mark; Brown, D. Murray
doi: 10.2134/agronj1994.00021962008600030009xpmid: N/A
Efforts to construct models of forage yield and quality loss during the field drying of hay are hindered by a lack of quantitative information concerning several modes of loss. This study attempted to quantify leaching and rainfall‐induced leaf shatter from drying alfalfa (Medicago sativa L. ‘Magnum’) forage. A rainfall simulator was used to treat samples from four forage cuttings in 1989 and 1990 at four levels of tissue moisture between 760 and 150 g kg−1 (wet basis). Rainfall amounts of 0 (control), 5, 10, 15, and 20 mm were used at intensity levels of 20 and 40 mm h−1. Leaves lost due to rainfall were collected, samples of forage tissue were analyzed for quality and yield changes and samples of leachate water were collected from beneath hay samples for analysis. Results showed that leaf shatter is not directly induced by rainfall. Analysis of forage tissue showed that leaching of soluble dry matter caused dry weight losses and increases (P ≤ 0.05) in the proportion of fiber in tissue. Leachate analysis provided a more precise measure of leaching losses. Analysis of leachates for total dissolved and suspended dry matter demonstrated that leaching increases with rainfall amount and as tissue moisture levels decline. At 700 g kg−1 (wet basis) moisture, leaching losses reached only 0.3% of initial sample dry matter, while at 170 g kg−1 moisture they were as great as 1.7%. Leaching was also greater (P ≤ 0.05) under rainfall at 20 mm h−1 than 40 mm h−1. A regression equation generated from the leachate data can be used to model leaching losses within prescribed limits.
doi: 10.2134/agronj1994.00021962008600030010xpmid: N/A
Grain yield of naked oat (Avena sativa var. nuda L.) is lower than that of conventional hulled cultivars. This field study was conducted to determine yield component differences between naked and conventional oat and to assess the potential of naked oat as a grain crop for northern environments. Studies were conducted at the Viikki Experimental Farm, University of Helsinki, Finland, in 1991 and 1992. Grain yield and 24 morphophysiological traits of 10 naked and 6 hulled lines were compared. Grain yield was 30% lower in the naked lines than in the hulled ones. Due to the high hull content ( ≈ 25%) of conventional lines, they produced only 10% higher groat yields than the naked oat lines. Naked lines had fewer panicles per square meter, due to their lower emergence, suggesting that a 10% increase in planting density of naked lines may result in equal groat yields of naked and conventional lines. Compared with hulled lines, naked lines had higher vegetative phytomass associated with lower harvest index. When grains were dehulled, the harvest index of naked lines did not differ significantly from that of conventional lines. The naked oat lines were characterized by fewer spikelets per panicle and more grains per spikelet compared with hulled lines. To achieve high grain yield and increase the competitive ability of naked oat, improvement in partitioning photosynthetic assimilates into grain is needed.
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