Agronomy Journal

Mahmood, Rezaul; Hubbard, Kenneth G.

doi: 10.2134/agronj2002.7230pmid: N/A

Daily incident solar radiation is an important input for numerous crop growth simulation models. However, lack of recorded solar radiation is a significant impediment for most crop–climate studies. The present study aimed to overcome the problem of sparse historical data of solar radiation over the northern Great Plains. The approach was to develop a physically based solar radiation model wherein estimates were possible with minimum input data. In addition, this study investigates impacts of time of observation bias on the model formulation. The proposed model (M‐H) requires measured daily range of air temperature (maximum minus minimum) and estimated daily clear‐sky solar radiation. Daily weather data (including solar radiation measurements) for nine stations with observations from 1990 through 1998 were used for formulation of the final model. To determine potential bias associated with the reporting time, three times—0800, 1600, and 2400 h—were tested. Based on superior performance, the solar radiation model formulated with 2400‐h reporting time data from Akron, CO, was selected for the whole region. The model underestimated high values. Local‐scale advection and frontal passage were apparently responsible for this bias. This proposed model was also compared with two forms of the Bristow–Campbell (B‐C) model. Both of these forms show significant improvement for 2400‐h observation time. One particular form of the B‐C model performs slightly better than the model proposed here. However, it also underestimates high values like the M‐H model and shows slight regional bias. This study finds that, overall, the M‐H model is more stable than the B‐C model.

Baumann, Daniel T.; Bastiaans, Lammert; Kropff, Martin J.

doi: 10.2134/agronj2002.7340pmid: N/A

Intercropping leek (Allium porrum L.) with celery (Apium graveolens L.) is an option to reduce growth and reproductive potential of weeds while maintaining productivity. In this study, a combined modeling approach is used to optimize a leek—celery intercropping system with respect to crop yield, product quality, and weed suppression. An ecophysiological model for interplant competition was used to simulate yield and product quality of the crops as well as biomass and seed production of the weed Senecio vulgaris L. for a wide range of crop mixtures and weed infestations. The results of the simulations were summarized using a descriptive hyperbolic yield–density model, which then allowed evaluation of the intercropping system in terms of productivity, product quality, and ability to suppress weeds. In a weed‐free mixture, the competitive ability of celery was six times higher than that of leek. With respect to late‐emerging S. vulgaris, the relative competitive ability of leek was 5.4 times lower than that of celery. Replacing two leek plants of a leek monoculture by one celery plant resulted in almost 20% biomass reduction of late‐emerging S. vulgaris. Crop mixtures with a leek density of about 20 plants m−2 and a leek/celery ratio of 2 proved to be the optimum intercropping system, given the current price ratios. Compared with leek monoculture, profitability was maintained, and late‐season weed suppression was greatly increased, resulting in reduced weed seed production.

Boote, Kenneth J.; Mínguez, María Inés; Sau, Federico

doi: 10.2134/agronj2002.7430pmid: N/A

Crop growth models are valuable tools for integrating our understanding of physiological processes and for hypothesizing and evaluating crop management strategies. Our objective was to adapt the CROPGRO model to simulate the growth and yield of faba bean (Vicia faba L.). The CROPGRO model simulates different grain legume species using external parameter files that describe species process sensitivity to environment plus files describing cultivar differences. Specific objectives were to develop a species file and one cultivar file for faba bean based on: (i) values and relationships from the literature and (ii) comparison with observed growth data on faba bean grown in Cordoba (Spain). A systematic procedure was followed to develop relationships and values for the species and cultivar files. Base temperatures for processes of this cool‐season legume are typically between 0 to 2°C for photosynthetic, vegetative, and reproductive processes while corresponding optimum temperatures vary from 22 to 30°C. After adaptation, the model accurately predicted total crop dry matter accumulation, pod mass, and partitioning to plant components. High seed yields of faba bean exceeding 6000 kg ha−1 were predicted in agreement with observed data. Sensitivity analyses on sowing date showed optimum yields from early winter sowing at Cordoba and late winter sowing in northern Europe. Adapting an existing mechanistic model such as CROPGRO had advantages because many processes were similar across species and well simulated. The primary adaptation required was to change the cardinal temperature sensitivities of growth processes, based on faba bean literature or by analogy to other species.

Giasson, Elvio; Bryant, Ray B.; Bills, Nelson L.

doi: 10.2134/agronj2002.7570pmid: N/A

Manure allocation on dairy farms to meet crop nutrient requirements, minimize environmental risks of nutrient loss, and maximize economic returns is a complex management decision. A multiple‐criteria, mathematical programming approach was developed to assess decision‐making with respect to manure allocation decisions at the farm scale. The objective function to be optimized includes several subfunctions developed for considering economic and environmental indicators, such as the Phosphorus Site Index. The structure of the nonlinear model allows the planner to change the importance among subfunctions, making it possible to obtain solutions that meet different management objectives for manure allocation. Optimization results for a New York State dairy farm were compared with recommendations made by a farm planner. The results show that using this optimization model allowed the total amount of manure within the farm to be applied, satisfying the nutrient requirements and keeping the P‐Index low in all fields where manure was applied. The optimized recommendation resulted in a 31% reduction in the average P‐Index weighted by field area and in a 50% reduction in the standard deviation of the P‐Index among fields, mainly because manure application was minimized in fields with higher soil‐test P and with higher P transport factor. This approach is a definite improvement over current practices used in nutrient management planning, but due to difficulties associated with nonlinear programming, this software is not easily adapted for general use.

Beyaert, Ronald P.; Schott, Jacqueline W.; White, Peter H.

doi: 10.2134/agronj2002.7670pmid: N/A

Minimum tillage has been shown to slow early corn (Zea mays L.) growth and reduce grain yields in some soil types and under some climatic conditions. To overcome these limitations, the no‐till (NT) system can be modified by incorporating residues and loosening the soil in a zone over the center of the row while leaving the interrow area untilled. This study compares soil temperatures and corn growth and productivity under zone till (ZT), NT, and conventional tillage (CT) systems in a coarse‐textured soil (Psammentic Hapludalf) located in southwestern Ontario, Canada. Soil temperature at the 4‐cm depth decreased with decreasing tillage intensity from CT to NT during warmer years but was similar in CT and ZT during a cooler year. This resulted in reduced growing degree days in the seed zone with decreasing tillage. Lower soil temperatures in NT did not delay the initiation of corn seedling emergence but did reduce the rate of emergence compared with CT plots. Corn growth rates were found to be similar among tillage systems in the early part of the growing system but were higher for both the ZT and NT systems during late vegetative and early reproductive growth. Grain yields increased as tillage intensity decreased in a year with drier conditions at tasseling but were similar across tillage systems in the other 2 yr. These results suggest that converting a NT system to a ZT system would neither result in significantly higher yields, nor cause a serious grain yield reduction relative to CT.

Seguin, Philippe; Sheaffer, Craig C.; Schmitt, Michael A.; Russelle, Michael P.; Randall, Gyles W.; Peterson, Paul R.; Hoverstad, Tom R.; Quiring, Steve R.; Swanson, Doug R.

doi: 10.2134/agronj2002.7750pmid: N/A

Autotoxicity may reduce plant population and productivity of alfalfa (Medicago sativa L.) reseeded into winterkilled alfalfa stands; however, the interaction of important variables such as reseeding delay, stand age, and cultivar with autotoxicity has not been evaluated. We determined the effects of stand age (1‐, 2‐, or 3‐yr‐old alfalfa stands), reseeding delay (none or 2‐wk delay) after plowing the original stands in May, and cultivar reseeded (‘5262’ or ‘Wrangler’) on populations and productivity of reseeded alfalfa. Oat (Avena sativa L.), corn (Zea mays L.), or tall fescue (Festuca arundinaceae Schreb.) served as controls. There was no consistent evidence for autotoxicity in the reseeding year, as populations and forage yields were similar when seeding followed alfalfa or the control crops, regardless of the age of the previous alfalfa stand or the alfalfa cultivar reseeded. Delaying seeding had inconsistent effects on alfalfa plant population but consistently reduced yields in the seeding year, with yields averaging 4.9 and 6.3 Mg ha−1 with and without a 2‐wk reseeding delay, respectively. In three of six experiments, yields at the first harvest in the year following reseeding averaged 15% lower following alfalfa than a control crop (3.6 and 4.2 Mg ha−1, respectively), suggesting that alfalfa autotoxic response may be delayed. The lack of consistent evidence of autotoxicity, coupled with yield reductions in the seeding year associated with delayed seeding, suggest that the recommendation to delay alfalfa reseeding 2 wk following plowing of winterkilled stands may be unjustified.

Brummer, E. Charles; Moore, Kenneth J.; Bjork, N. Charles

doi: 10.2134/agronj2002.7820pmid: N/A

The yield of alfalfa (Medicago sativa L.) during the establishment year is typically less than that from fully established stands. Because nondormant cultivars produce more growth during autumn than dormant cultivars, a mechanism to increase yield during the establishment year in northern areas of the USA could be to mix seed of nondormant and adapted cultivars at planting. The objective of this experiment was to determine if establishment year yield could be improved by seeding dormant–nondormant mixtures without adversely affecting yield in the succeeding year. Two dormant–nondormant mixtures (‘Vernal’–‘Mecca II’ and ‘5454’–‘5939’) with 10, 30, or 50% of the nondormant cultivar and pure stands of all four cultivars were seeded in field studies near Ames, Nashua, and Castana, IA, in April 1998. Four forage harvests were taken in 1998, including one in late October, and in 1999. Plants were counted in May and October 1998 and in June 1999. Plant numbers among treatments were similar during 1998. Stand mortality in spring 1999 increased as the nondormant percentage increased, except that 10% nondormant plots had slightly more plants than 0% plots. In 1998, total forage yield increased linearly with increasing percentage of nondormant seed, but nutritive value in October 1998 declined slightly with increasing percentages of nondormant seed. In 1999, yield declined linearly as the percentage of nondormant seed increased; plots with 10% nondormant seed yielded less than the pure stands of dormant cultivars. We do not recommend mixing any nondormant seed with adapted dormant cultivars at planting.

Jennings, John A.; Nelson, C. Jerry

doi: 10.2134/agronj2002.7860pmid: N/A

Published intervals for avoiding autotoxicity when reseeding alfalfa (Medicago sativa L.) after alfalfa range from 2 wk to more than 1 yr. Intervals between killing old alfalfa stands with herbicides and reseeding alfalfa were compared in field experiments established in 1992 (Locations 1 and 2) and 1993 (Location 3) near West Plains, MO. Soils were Poynor cherty silt loam (loamy‐skeletal over clayey, siliceous, mesic Typic Paleudult), Ashton silt loam (fine‐silty, mixed, mesic Mollic Hapludalf), and Waben very cherty silt loam (loamy‐skeletal, siliceous, mesic Ultic Hapludalf), respectively. Main plots were 18‐, 12‐, 6‐, 0.75‐, and 0.5‐mo rotation intervals before a common May planting date. Subplots were insecticide and fungicide treatments at planting. Insecticide or fungicide treatment did not affect plant density or yield during the establishment year or two subsequent years. Among years, plant densities for the 0.75‐ and 0.5‐mo rotation intervals ranged between 12 and 19.2% lower (P < 0.05) than that of the 18‐mo control interval, and yields for the 6‐ and 0.5‐mo intervals ranged between 6.3 and 10.3% lower than that of the control (P < 0.05). Although plant density of the 0.75‐mo rotation interval was lower, yield was similar to the 18‐mo control due to incomplete kill of old plants. Plant density and dry matter yield remained ranked according to rotation interval from the seeding year through the third year, suggesting an autoconditioning effect during establishment that was retained at the population level. A rotation interval of at least 12 mo is suggested before reseeding alfalfa after alfalfa in the lower Midwest.

Lauriault, Leonard M.; Kirksey, Rex E.; Donart, Gary B.

doi: 10.2134/agronj2002.7920pmid: N/A

Winter months in the Southern High Plains of the USA have the lowest precipitation. As a result, producers using tall wheatgrass [Agropyron elongatum (Host) Beauv.] may get higher production in the spring and possibly throughout the growing season with additional irrigation. Also, growers need information about interactions between soil moisture and N fertilizer to maximize productivity. In a split‐plot study conducted at the New Mexico State University Agricultural Science Center at Tucumcari from 1997 to 1999, tall wheatgrass furrow‐irrigated monthly from April to September was irrigated once, twice, or not irrigated during winter as the whole‐plot treatment. For subplot treatments, tall wheatgrass annually received 168 kg N ha−1 split into two, three, or four equal applications. Tall wheatgrass irrigated in the winter yielded more dry matter (DM) over the 3 yr than unirrigated tall wheatgrass (11.72, 12.10, and 13.55 Mg ha−1 for tall wheatgrass not irrigated, irrigated once, or irrigated twice, respectively). Tall wheatgrass fertilized three or four times outyielded tall wheatgrass fertilized twice (11.08, 12.85, and 13.44 Mg ha−1 for two, three, and four N applications, respectively). No interaction occurred between the irrigation and N treatments. A year × harvest × N effect existed in which a mid‐December N application, preceded and followed by precipitation, produced approximately 1 Mg ha−1 more DM than unfertilized tall wheatgrass in the first harvest the following year. Both supplemental winter irrigation and N application scheduling offer opportunities for tall wheatgrass producers to increase production in the Southern High Plains of the USA.

Schmidt, John P.; DeJoia, Aaron J.; Ferguson, Richard B.; Taylor, Randal K.; Young, R. Kris; Havlin, John L.

doi: 10.2134/agronj2002.7980pmid: N/A

Improving N management for corn (Zea mays L.) production with precision agriculture technologies requires that spatial N recommendations adequately represent in‐field variability in N availability. Our objective was to evaluate corn response to increasing N rates in several in‐field locations that represented the range of soil organic matter (OM) content in the field. In a 2‐yr study, three center pivot–irrigated fields were selected in south‐central Kansas and south‐central Nebraska. Four or five locations were selected within each field. At each location, five or six N treatments (0–336 kg N ha−1) were surface‐applied early in the growing season. The minimum N rate to achieve maximum yield varied by as much as 130 kg N ha−1 among in‐field locations at three site‐years. The least amount of N to achieve maximum yield did not coincide with locations representing greater soil OM. Yield response at two site‐years was the same among in‐field locations; however, mean yield among in‐field locations varied by as much as 4.2 Mg ha−1, representing potential for improvement in N use efficiency. Leaf tissue N was below the critical threshold for 60 to 100% of observations at three different in‐field locations but below the critical threshold for <35% of the observations at all other in‐field locations. The reason for the discrepancy in N availability among in‐field locations was not conclusively identified but was not only related to soil OM content. Variable N recommendations based only on soil OM is too simplistic to reflect variability in N availability within a field.