Eight field studies were conducted in soybeans at seven locations in Kansas over a 3-yr period to examine the efficacy of using reduced rates of the herbicides acifluorfen, bentazon, chlorimuron, and tank mixes of acifluorfen and bentazon. POST applications of these herbicides at 1/2X rates at 2 wk after planting (WAP) resulted in broadleaf weed control similar to that obtained from standard treatments of 1X rates applied at 4 WAP at six of seven studies with acifluorfen, bentazon, and acifluorfen plus bentazon and at five of seven studies with chlorimuron. One-quarter rates applied 2 WAP were equivalent to standard treatments for broadleaf weed control in four of seven studies with acifluorfen and chlorimuron, five of seven studies with bentazon, and six of seven studies with acifluorfen plus bentazon. One cultivation at 4 WAP, increased the broadleaf weed control with all herbicide treatments.

Response of soybean [Glycine max (L.) Merr.] to changes in row spacing and seeding rate have been variable. Some researchers have reported grain yields to be higher with the use of narrow row spacings. Other investigators have found that wide row spacings provided grain yields equal to or greater than those obtained with narrow row spacings. This study was designed to determine the influence of environment on the optimum row spacing and seeding rate for soybean. Eleven field experiments were established in Kansas from 1991 to 1993. Four seeding rates in 1991 and five seeding rates in 1992 and 1993, ranging from 52 272 to 261 360 seeds/acre, were used in 8‐ and 30‐in. rows. At high yielding sites, maximum grain yields were higher with 8‐in. rows than with 30‐in. rows. If moisture stress reduced grain yields, maximum yields were greater with 30‐in. rows than with 8‐in. rows. Response to changes in seeding rate varied between row spacings depending upon environmental conditions. Under high‐yielding conditions, grain yields were maximized with 30‐in. rows at approximately 115 000 seeds/acre, whereas seeding rates of 203 000 to 232 000 seeds/acre were required to maximize grain yields with 8‐in. rows. Under conditions of limited soil moisture, grain yields were not affected by changing seeding rates. At sites with adequate soil moisture, mature plant heights increased as seeding rates increased. At moisture‐deficient sites, plant height was not significantly affected by increased seeding rates. Research Question Recommendations for soybean row spacing and seeding rate are generally constant within a geographical area regardless of yield goal or yield potential. This research was designed to determine the influence of environment on the optimum row spacing and seeding rate for soybean. Literature Summary Many researchers have reported that soybeans planted in narrow row spacings produced higher yields than did soybeans planted in wider row spacings. Other investigators found little or no yield increase with the use of narrow row spacings. Some researchers have reported that soybeans planted in narrow rows had greater water‐use efficiency than did soybeans planted in wider rows. Other investigators, however, found that, under conditions of severe water stress, water‐use efficiency was greater with wide rows than with narrow rows. Yield response to changes in plant population usually have been small and often inconsistent. Generally, increasing plant populations has increased plant height at maturity. It has been reported that higher plant mortality occurred with wide rows than with narrow rows. Study Description This research was conducted from 1991 to 1993 at 11 dryland locations in Kansas. In 1991, four seeding rates ranging from 52 272 to 209 088 seeds/acre were used in 8‐ and 3041‐1. rows. In 1992 and 1993, an additional seeding rate of 261 360 seeds/acre was added. Plant populations were determined 5 wk after planting. Plant lodging, mature plant heights, and grain yields were measured at maturity. Corsica was the ...

Soil erosion from agricultural fields is a fundamental water quality and quantity concern throughout the U.S. Watershed models can help target general areas where soil conservation measures are needed, but they have been less effective at making field-level recommendations. The objectives of this study were to demonstrate a method of field-scale targeting using ArcSWAT and to assess the impact of topography, soil, land use, and land management source data on field-scale targeting results. The study was implemented in Black Kettle Creek watershed (7,818 ha) in south-central Kansas. An ArcGIS toolbar was developed to post-process SWAT hydrologic response unit (HRU) output to generate sediment yields for individual fields. The relative impact of each input data source on field-level targeting was assessed by comparing ranked lists of fields on the basis of modeled sediment-yield density (Mg ha-1) from each data-source scenario. Baseline data of field-reconnaissance land use and management were compared to NASS and NLCD data, 10 m DEM topography were compared to 30 m, and SSURGO soil data were compared to STATSGO. Misclassification of cropland as pasture by NASS and aggregation of all cropland types to a single category by NLCD led to as much as 75% and 82% disagreement, respectively, in fields identified as having the greatest sediment-yield densities. Neither NASS nor NLCD data include land management data (such as terraces, contour farming, or no-till), but such inclusion changed targeted fields by as much as 71%. Impacts of 10 m versus 30 m DEM topographic data and STATSGO versus SSURGO soil data altered the fields targeted as having the highest sediment-yield densities to a lesser extent (about 10% to 25%). SWAT results post-processed to field boundaries were demonstrated to be useful for field-scale targeting. However, use of incorrect source data directly translated into incorrect field-level sediment-yield ranking, and thus incorrect field targeting. Sensitivity was greatest for land use data source, followed closely by inclusion of land management practices, with less sensitivity to topographic and soil data sources.

In the greenhouse, soil applications of primisulfuron (40 g ai ha–1) reduced growth of emerged rhizome johnsongrass plants more than nicosulfuron (40 g ai ha–1). Both herbicides reduced growth more when applied to foliage only; a further decrease in growth did not occur for applications to both soil and foliage. Primisulfuron did not completely prevent regrowth of johnsongrass with any application method. Nicosulfuron prevented regrowth when applied to the foliage and to both soil and foliage. In single-year field studies in corn at four dryland sites and two irrigated sites, 50:50 split applications of primisulfuron (40 g ai ha–1) and nicosulfuron (35 g ai ha–1) approximately 2 wk apart provided the most consistent rhizome johnsongrass control compared with early or late single applications when visually rated 8 wk after the first application. Nicosulfuron treatments were more effective than primisulfuron treatments at both dryland sites the first year and at one of two dryland sites the second year. Primisulfuron and nicosulfuron at the irrigated site the first year were equivalent in efficacy. Nicosulfuron was more effective than primisulfuron at the irrigated site the second year. Primisulfuron or nicosulfuron treatments more than doubled corn yields at the dryland sites both years regardless of application timing. Split applications of primisulfuron or nicosulfuron provided the highest yields (approximately 80% increase over untreated plots) at the irrigated site the first year. All treatments provided equivalent yield increases (approximately 50%) the second year.

Corn (Zea mays L.) production practices have to be evaluated periodically to ensure that producers are fully using improvements in hybrids. A 2‐yr study was conducted to assess corn yield response to plant population, planting dates, and hybrid maturity. The study was conducted at three sites during the 1994 and 1996 growing seasons. A 102 and a 113 d relative maturity corn hybrid were established at plant populations of 14 000, 20 000, and 26 000 plants/acre. Planting dates in early April, May, and June were also used. At two locations, delaying planting from April to May decreased yields slightly. At the third location, yields increased 27 bu/acre as planting was delayed until early May. Delaying planting at this location resulted in ear development occurring after a period of severe drought, which reduced yields with the April planting. At all three locations, delaying planting until early June reduced yields as a result of ear development under higher temperatures and grain fill occurring under cooler temperatures. Increasing population from 14 000 to 20 000 plants/acre resulted in a yield increase of 14 bu/acre across all six environments. Grain yields increased an additional 4 bu/acre when plant population was increased to 26 000 plants/acre. When planted in April or May, the full season hybrid produced higher yields than the earlier maturing hybrid. Corn producers in north central and northeast Kansas can increase corn yields by using planting dates in April and a population of approximately 26 000 plants/acre. Research Question Corn production practices have to be evaluated periodically to determine whether management changes are needed to fully utilize improvements in water and nutrient use efficiency as well as shade, drought, cold, and pest tolerance. Increased tolerance to shade and drought stress should enable producers to increase plant populations, resulting in higher yields in the more productive years without the risk of yield loss during a drought year. Greater cold tolerance and seedling vigor should allow earlier planting dates, thus enabling producers to take advantage of fuller season hybrids. The objectives of this study were to evaluate the effects that plant population, planting date, and hybrid maturity have on corn yield. Literature Summary Studies conducted in 1966 and 1967 in Kansas indicated that dryland corn yields increased as plant population increased until reaching a maximum at approximately 20 000 plants/acre and then declined as plant population continued to increase. However, recent studies have reported that the corn yield response to plant population was quadratic with yields reaching a plateau rather than declining at higher plant populations. Corn producers in northeast Kansas may plant earlier to increase the growing season length or to move harvest earlier in the year to distribute labor. Approximately 260 heat units can be accumulated during April in northeast Kansas, yet little data exist to quantify the effects that these additional heat units have on corn yields. As...