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yield response to N fertilizer is important in providing effective N management recommendations over a wide Efficient use of N fertilizer for corn (Zea mays L.) production range of soil-climate conditions, minimizing the potenis important for maximizing economic return and minimizing NO 3 leaching to groundwater. The objective of this study was to evaluate tial for negative environmental impacts. grain yield response to irrigation rate and N rate and timing forNumerous studies have emphasized the importance irrigated corn in the sandy soils along major Kansas waterways. Nitroof considering the effects of water management on NO 3 gen treatments included 300 and 250 kg N ha Ϫ1 applied at planting; movement under irrigated corn (Watts and Martin, 1981; 250 kg N ha Ϫ1 applied at planting (one-half) and sidedress (one-half); Hergert, 1986;Spalding et al., 2001). Endelman et al.185 kg N ha Ϫ1 applied at planting (one-third) and sidedress (two- (1974) reported that as little as 2.54 cm of irrigation or thirds); 125 kg N ha Ϫ1 applied at planting (one-fifth) and sidedress rainfall can move soil NO 3 15 to 20 cm in a loamy sand (two-fifths, two-fifths); and 0 kg N ha Ϫ1 . Nitrogen treatments were soil. Considering that the average rainfall duplicated at one site for each of two irrigation treatments (IS): 1.0ϫ from mid-April to mid-June in south-central Kansas is (optimal) and 1.25ϫ (25% Ͼ optimal). A split application of 185 kg 21.2 cm (Kansas State Univ. Res. and Ext., 2004), the N ha Ϫ1 was sufficient to achieve maximum corn yield at every location, and in most instances 125 kg N ha Ϫ1 was sufficient. These rates were

With renewed interest in maintaining our soil resources, it is important to establish criteria that can describe and quantify the effect of different crop management practices on soil organic matter (SOM). We conducted this study to assess changes in SOM and other soil properties after long‐term (>10 yr) continuous corn (Zea mays L.; CC) and corn‐soybean rotation [Glycine max (L.) Merr.; C/SB] with and without fertilizer. Soil samples were collected from two furrow‐irrigated CC and C/SB rotations on a Crete silt loam (fine, montmorillonitic, mesic Pachic Argiustoll) and a Eudora loam (coarse‐silty, mixed, mesic Fluventic Hapludoll). Long‐term (350‐d) laboratory incubation at optimum moisture and temperature conditions measured potentially mineralizable C (PMC) and N (PMN) as a measure of the active fraction of soil organic C and N. Microbial biomass C (MBC) and N (MBN), organic C and N, pH, and texture also were determined. Crop rotations that included high‐residue‐producing crops such as corn and addition of fertilizer increased soil organic C and N. Crop rotation did not affect PMC in the Crete soil, but addition of fertilizer significantly increased PMC by 32%. The PMN in both soils was not affected by crop rotation or fertilizer addition. Inclusion of soybean in the rotation decreased the stable and active fractions of organic C and N. Changes in soil organic C and N in response to crop rotation and fertilizer addition were related to the estimated amount of crop residues returned to the soil and to soil texture.

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 ...

An in-row competition study was conducted in 1991 and 1992 near Silver Lake, KS to determine the relationship of noncultivated common sunflower density to soybean yield, PAR at the soybean canopy, and common sunflower dry matter production. Because of environmental differences, year main effect interactions occurred, so results are presented by year. For example, 0.3 common sunflower plant/m2produced 4030 kg/ha of aboveground dry matter in 1991 and 1300 kg/ha in 1992. Soybean yield reduction ranged from 19 and 17% with 0.3 common sunflower plant/m2to 97 and 95% with 4.6 plant/m2, in 1991 and 1992, respectively. Assuming a treatment cost of $35/ha and a soybean market price of $0.21/kg, economic threshold levels were 0.1 common sunflower plant/m2in 1991, and 0.07 in 1992. Common sunflower at 0.3 plant/m2reduced PAR at the soybean canopy by 390 and 300 μE/m2/s, or 24 and 18% in 1991 and 1992, respectively. We conclude that the ability of common sunflower to intercept PAR above the soybean canopy is an important component in its interference with soybean.

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...

Increasing crop N use efficiency and minimizing environmental risk require an accurate assessment of N taken up by the crop from different sources. We conducted this study to: (i) compare the grain yields of corn (Zea mays L.) in monoculture and in rotation with soybean [Glycine max (L.) Merr.]; (ii) determine the contributions of N from fertilizer, soil, and legume residue to corn in the rotation; and (iii) compare N fertilizer recovery in monoculture and in rotation. Two existing (>10 yr) irrigated corn‐soybean rotation areas in Kansas were used. The soils were Crete silt loam (fine, smectitic, mesic Pachic Argiustolls) and Eudora loam (coarse‐silty, mixed, superactive, mesic Fluventic Hapludolls). To trace the N through the rotation, 15N microplots (2.4 m2) were established int he corn. Microplots also were established in soybean to separately follow 15N from roots + soil and shoots to corn. Crop rotation and fertilizer addition increased corn yield at both sites for two growing seasons. Averaged for 2 yr, the amount of N needed in the continuous corn to achieve yield equal to that in rotation with no N added was equivalent to 144 kg N ha‐1 in the Crete silt loam and 155 kg N ha‐1 in the Eudora loam. Response to N was greater on the Eudora loam, probably because of textural and organic matter differences. In the Eudora soil, significantly higher amounts of soil N were taken up at harvest by corn in rotation, whereas, in the Crete soil, corn in monoculture took up significantly higher amounts of soil N. Corn plants recovered 3 kg N ha‐1 (3%) from soybean residue in the Eudora soil and 5 kg N ha‐1 (14%) in the Crete soil. The main value of legume residue appears to be long‐term maintenance of soil N to ensure adequate delivery to future crops.