Agronomy Journal

Varga, Boris; Svečnjak, Zlatko; Pospisil, Ana

doi: 10.2134/agronj2001.935961xpmid: N/A

The use of intensive production systems (IPS) may substantially increase winter wheat (Triticum aestivum L.) grain yields in Croatia because the national average yield of 4.14 t ha−1 is low compared with the yield potential of currently grown cultivars. Field experiments were conducted during 1996 through 1998 to evaluate the agronomic responses of 15 modern cultivars grown at two seeding rates (440 and 770 seeds m−2) in both an IPS and an extensive production system (EPS). The IPS consisted of plowing at 30 to 32 cm; fertilization at 194, 130, and 130 kg ha−1 N, P, and K; and high input of crop protection chemicals. The EPS involved plowing at 20 to 22 cm; fertilization at 59, 104, and 104 kg ha−1 N, P, and K; and less effective herbicide application. Grain yields significantly increased in the IPS and averaged 7840 kg ha−1 compared with 5910 kg ha−1 for the EPS. This difference was due to a 16.8 and 19.6% increase in spike number and kernel number per spike, respectively, while 1000‐kernel weight for the IPS decreased by 6.0% compared with the EPS. Higher seeding rate maximized grain yields in both production systems except for one growing season in the IPS, primarily due to improved spike number. Cultivars responded similarly to seeding rates regardless of the production system. A significant interaction between cultivars and the two production systems was found because some cultivars were highly responsive to the IPS while others were not. Thus, cultivar selection is an important consideration for Croatian farmers when they decide to adopt the IPS.

Fischer, Albert J.; Ramírez, Hector V.; Gibson, Kevin D.; Da Silveira Pinheiro, Beatriz

doi: 10.2134/agronj2001.935967xpmid: N/A

When savannas in Latin America are brought into cultivation, rice (Oryza sativa L.) can be sown with the perennial grasses palisadegrass [Brachiaria brizantha (Hochst. ex A. Rich) Stapf] and signalgrass (B. decumbens Stapf) to harvest a grain crop while establishing a pasture to suppress weeds and provide grazing in subsequent years. However, these Brachiaria spp. can reduce upland rice yields. Rice cultivars need to be competitive with Brachiaria spp. to maintain yields but must allow Brachiaria spp. sufficient growth for pasture establishment. Field studies were conducted during 1994 and 1995 on a Typic Haplustox oxisol soil in the Eastern Plains of Colombia to evaluate the competitiveness of upland rice cultivars and to identify rice traits for competitiveness. Ten (1994) and 14 (1995) upland rice cultivars were grown with and without signalgrass in 1994 and palisadegrass in 1995. Rice cultivars differed substantially in their competitiveness. Rice yield losses ranged from 18 to 55%, and Brachiaria aboveground biomass ranged from 1.4 to 3.2 Mg ha−1 dry mass. Competition for light was critical; rice photon flux density interception, leaf area index [≥45 d after emergence (DAE)], and number of tillers (≥60 DAE) were correlated with competitiveness. No tradeoff between high yield potential and competitiveness was detected in these upland rice cultivars. Early maturity of rice is a desired characteristic for the rice–Brachiaria spp. association. The development of more‐competitive cultivars appears to be a viable approach for reducing herbicide dependency and improving profitability of Latin American rice–pasture intercropping systems.

Kurle, James E.; Grau, Craig R.; Oplinger, Edward S.; Mengistu, Alemu

doi: 10.2134/agronj2001.935973xpmid: N/A

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum (Lib.) de Bary, is an important soybean [Glycine max (L.) Merr.] disease in the North Central States. The effect of tillage, crop sequence, and cultivar on SSR incidence and soybean yield was evaluated in a 3‐yr on‐farm study conducted at Janesville, Sharon, and Waunakee, WI. In the study, arranged in a split‐split‐split‐split plot design, main plots were tillage: moldboard (MB), chisel plow (CP), or no‐till (NT); subplots were 1995 crops: corn (Zea mays L.), small grain, or soybean; sub‐subplots were 1996 crops: corn, small grain, or soybean cultivar. Sub‐sub‐subplots were soybean cultivars planted in 1997. In 1997, SSR incidence averaged >40% at Janesville and Waunakee, and <1% at Sharon; and was lowest in NT (P < 0.001) or when the soybean cultivar S19–90 was planted (P < 0.001). Planting corn or oat (Avena sativa L.) the preceding year (1996) reduced SSR incidence in 1997 (P < 0.001). Yield was highest in NT (P < 0.001), in S19–90 (P < 0.001), and following oat (P < 0.001). Sclerotial density was affected by tillage (P < 0.001). Apothecial numbers were greatest in MB and lowest in NT. Because brown stem rot, Phialophora gregata (Allington and Chamberlain) W. Gams, and SSR developed at Janesville, there was a simple linear relationship between yield and SSR incidence (R2 = 0.35, P < 0.01) only at Waunakee. Soybean yields were greatest when S19–90 was planted in NT following corn or oat.

Schmitt, Michael A.; Lamb, John A.; Randall, Gyles W.; Orf, James H.; Rehm, George W.

doi: 10.2134/agronj2001.935983xpmid: N/A

Predicted physiological factors and a limited number of field studies have resulted in debate regarding the recommendation of in‐season fertilizer N for soybean [Glycine max. (L.) Merrill]. The objective of our research was to evaluate several in‐season N fertilization strategies on soybean seed yield response as well as to measure the effect of fertilizer N additions on late‐season plant N concentrations and accumulation, seed N removal, seed protein, and seed oil composition. The research was conducted at 12 sites in the southern soybean‐growing region of Minnesota in 1998 and 1999. A combination of (i) application time (July vs. August), (ii) placement method (broadcast vs. knifed), and (iii) N source (urea vs. poly‐coated urea) gave five N treatments plus a control at all sites. Seed yield did not respond to the fertilizer N treatments at any of the 12 sites; however, a combined analysis indicated a significant increase (generally less than 0.06 Mg ha−1) from using polymer‐coated urea or applying the urea in August. Herbage dry matter (DM) and herbage N concentrations at the R6 stage were not affected by any of the N fertilizer strategies. Although soybean seed protein was statistically different among the treatments, protein was only increased 0.4 g kg−1. Soybean oil concentration was not affected by fertilizer treatments. In general, polymer‐coated urea, knifed applications, and August applications increased soil NO3–N in the 0‐ to 30‐cm layer at R6 relative to standard urea, broadcast applications, and July applications. Even though in‐season N fertilizer created greater levels of available soil N at all 12 sites during soybean pod filling, seed yield was not improved compared with unfertilized control plots at any site. As a result, the University of Minnesota does not recommended in‐season N fertilizer applications for soybean production.

Jesus, Waldir Cintra; Vale, Francisco Xavier Ribeiro; Coelho, Reginaldo Resende; Costa, Luiz Claúdio

doi: 10.2134/agronj2001.935989xpmid: N/A

Measurement of leaf area index (LAI) is important in studies of plant growth. Based on this concept, the analysis of crop growth has moved from classical growth analysis to mechanistic models, via functional growth analysis. Leaf area index is a major variable in mechanistic crop growth models and in models that attempt to simulate loss caused by pathogens. A field experiment was carried out from May through August 1998, using common bean (Phaseolus vulgaris L. cv. Carioca), in a randomized complete block design with two methods of LAI evaluation and three replications. The objective of this study was to compare the applicability of the LAI‐2000 Plant Canopy Analyzer with the central leaflet width method used to estimate LAI in common bean. The high correlation (r2 = 0.97) observed between the two methods used to estimate LAI shows agreement between them. The results of this study indicated that the LAI‐2000 can be used to estimate the LAI of common bean.

Harmoney, Keith R.; Moore, Kenneth J.; Brummer, Edward C.; Burras, C. Lee; George, J. Ronald

doi: 10.2134/agronj2001.935992xpmid: N/A

Pastures typically have diverse landscapes, and resulting soil conditions and plant composition can vary within small area units. This study was performed to quantify the spatial variation in legume contribution to the plant community when seeded into established perennial cool‐season grass pastures. Pastures were interseeded with an 11‐legume mixture and divided into three stocking methods (continuous, rotational, and nongrazed), with each stocking method containing five landscape positions (summit, backslope, toeslope, opposite backslope, and opposite summit). Grass and legume components were sampled three times annually between 1996 and 1998. Backslopes had greater legume dry matter (DM) composition (161 g kg−1) than either summit (62 g kg−1) or toeslope positions (7 g kg−1), and total legume concentrations increased over years. Legume composition consisted mostly of red clover (Trifolium pratense L.), birdsfoot trefoil (Lotus corniculatus L.), and white clover (T. repens L.). Species richness and Shannon–Weiner diversity index (H’dm) for the legume functional group were also greatest on backslope landscape positions, especially in continuously and rotationally stocked pastures. Legume DM composition showed a positive linear relationship with legume species richness in continuous, rotational, and nongrazed pastures (r2 = 0.76). The H’dm showed a positive linear relationship with legume DM composition in only rotationally stocked paddocks (r2 = 0.88). The legume component at grazed backslope sites filled a niche left unoccupied by the grass component. Species and site recommendations for pasture improvement and management should be made based on landscape position and stocking method.

Stout, William L.; Weaver, Stefan R.; Elwinger, Gerald F.

doi: 10.2134/agronj2001.9351000xpmid: N/A

Grass–legume pastures that rely on biologically fixed N are often N deficient in the spring. Early season N applications to grass–clover pastures can help overcome this deficiency. Our objective was to test the effects of early season N application and harvest height on total dry matter (DM) yield and clover fraction of a grass–clover sward in the northeast USA. The study was conducted for 3 yr (1996–1998) at the Russell Larson Agricultural Research Center in Rock Spring, PA (40°48′N, 77°52′W; 330 m above sea level). The soil on the site is a Hagerstown silt loam (Typic Hapludalf, fine, mixed, mesic). The effect of early season N fertilization (0, 22.4, 44.8, and 89.6 kg ha−1) was measured on an orchardgrass (Dactyls glomerata L. cv. Pennlate)–white clover (Trifolium repens L. cv. Will) sward harvested at three sward heights (15, 22.5, and 30 cm). Increasing N fertilization and target sward harvest height (TSHH) generally increased the early season total DM yield and reduced the clover fraction in the sward. However, by the end of the growing season, the clover fraction from the fertilized treatments was identical to that of the unfertilized treatments. Total early season DM yields on mixed grass–clover swards were increased by 20% with an application of 45 kg N ha−1. Also, maintaining a 15‐cm TSHH along with 45 kg N ha−1 would maximize the clover fraction in the sward.

Caballero, Rafael; Alzueta, Carmen; Ortiz, Luis T.; Rodríguez, Maria Luisa; Barro, Carmen; Rebolé, Almudena

doi: 10.2134/agronj2001.9351006xpmid: N/A

Mixed cereal and sheep (Ovis aries) production systems in the Mediterranean area and the Middle East region rely on annual forage legumes as a source of complementary forage. Fractionation of carbohydrates (CHO) and crude protein (CP) into chemical entities of refined biological significance may improve the forage utilization of these feed resources. Fresh and dried (field‐cured) common vetch (Vicia sativa L.) samples were collected during two growing seasons (1996–1997 and 1997–1998) at La Poveda Field Station in central Spain with the objective of determining chemical CHO and CP fractions required for application of new feed models (Cornell System). Fresh and dried samples were harvested at three maturity stages—flowering (>50% of plants with flowers), seed filling phase 1 (280 g DM kg−1 seed), and seed filling phase 2 (380 g DM kg−1 seed)—and the treatments were arranged in a completely randomized design. Nonfiber carbohydrates (NFC) and neutral‐detergent fiber (NDF), corrected for neutral‐detergent insoluble protein (NDIP), were evenly distributed in fresh and dried samples, and were not affected by maturity. The B1 and B2 CHO fractions were the most abundant with mean values of 342 and 303 g kg−1 of total carbohydrates (TC), respectively, across maturities, harvest forms, and years. Fraction CP B2 was the most abundant CP fraction with mean value of 408 g kg−1 of total CP. Fraction CP B3 was <100 g kg−1 of total CP and increased with maturity. Harvesting common vetch within the seed filling phase would increase ruminal escape protein in vetch.

Clifton‐Brown, John C.; Lewandowski, Iris; Andersson, Bengt; Basch, Gottlieb; Christian, Dudley G.; Kjeldsen, Jens Bonderup; J⊘rgensen, Uffe; Mortensen, J⊘rgen V.; Riche, Andrew B.; Schwarz, Kai-Uwe; Tayebi, Koeyumars; Teixeira, Fernando

Steiner, Jeffrey J.; Brewer, Tim G.; Griffith, Stephen M.

doi: 10.2134/agronj2001.9351020xpmid: N/A

Successful reintroduction of native species into landscapes requires an understanding of how introduced species invaded and became established. This study was conducted to determine the effect of temperature on interspecific seedling interference of two wetland grasses [sloughgrass (Beckmannia syzigachne Steud.) and tufted hairgrass (Deschampsia caespitosa L.)] native to the Pacific Northwest and tall fescue (Festuca arundinaceae Schreb. cv. Titan), a non‐native grass species. The relationships of species interference to the thermal response of Photosystem II (PS II) fluorescence reappearance ratio (FRR) and glutathione reductase (GR) thermal stability were also investigated using the Mantel product moment correlation (rm). Three combinations of two‐species replacement series experiments (sloughgrass–hairgrass mixture, sloughgrass–tall fescue mixture, and hairgrass–tall fescue mixture) were conduced in growth chambers, planted in five proportions (0.0:1.0, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1.0:0.0), and grown at four temperatures (5, 10, 20, and 30°C). The FRR and GR were measured at eight temperatures ranging from 5 to 40°C. Tall fescue aggressiveness, relative to sloughgrass and hairgrass, increased with increasing temperature. Sloughgrass and hairgrass ranked second and third, respectively, and were only more aggressive than tall fescue at 5°C. Peak FRR occurred at 15, 20, and 22.5°C for sloughgrass, hairgrass, and tall fescue, respectively. Seedling dry mass of species was correlated with the stability of GR and the average efficiency of the PS II apparatus over the range of growing temperatures (rm = −1.00 and 0.96, respectively). Tall fescue had greater PS II efficiency and GR stability under elevated temperatures than sloughgrass and hairgrass, which may explain why tall fescue has been able to dominate some wetland landscapes of the temperate Pacific Northwest.