Corn Cropping System Research Articles

Water use efficiency of a mixed cropping system of corn with grasses

A new cropping system of corn mixed with grasses was tried to make full and efficient use of water and to ease environmental problems such as soil erosion by water and wind in grain and forage feed production practices. Field experiments were conducted to investigate the water use efficiency under this mixture cropping system. Six treatments with two replicates were arranged as: bare field, corn only, rye only, alfalfa only, rye–corn mixture and alfalfa–corn mixture. Lysimeters were used to measure different components of water consumption in the crop fields for water use efficiency estimation. From the yields and water consumption of crops under different treatments, combined water use efficiency of corn and grasses were estimated. The results showed that WUEs in the mixed cropping fields of corn–grasses were much higher than those in the fields where only corn or grass were grown. Averaged WUE was 3.71 kg/m3 from the corn and rye mixture fields, 30% higher than that from the plots where only corn or rye were grown. Averaged WUE was 4.55 kg/m3 from the alfalfa and corn mixture fields, 60% higher than that from the fields where only corn or alfalfa were grown. Under the same conditions of irrigation, yields from the rye and corn mixture plots increased by 33%, as compared with those from fields where only corn or rye were grown. The yields from alfalfa and corn mixture fields were 61% higher than those from fields where only corn or alfalfa were grown. The experimental results also indicated that corn and alfalfa mixture cropping is better than a corn–rye mixture system.

Laboratory Calibration, In‐Field Validation and Use of a Soil Penetrometer Measuring Cone Resistance and Water Content

Concurrent and coincident measure of penetrometer cone resistance (PR) and water content (WC) were optimized by hourly in‐field validation of data from time domain transmissiometry (TDT) for WC and piezoelectric force sensor for PR. A piezoelectric force sensor coupled to a cone is followed by a helical wrapped TDT sensor on a single penetrometer shaft. Detailed laboratory calibrations, coupled with in‐field validations, were important to assure the quality of data, which facilitated detailed analyses of PR and WC patterns. The piezoelectric sensor relied on a calibrated spring for the in‐field validation. The calibration of the TDT sensor had three stages: a series of fluids of known dielectric constant; soil columns at known, variable water contents; and field soils at a range of ambient conditions. The penetrometer was used to study soil strength and WC behavior in time and space along 300‐m plots. The treatments were conventional and no‐till, each at two levels of traffic. The crop was corn (Zea mays L.), continuous and in rotation with soybean [Glycine max (L.) Merr.] and wheat (Triticum aestivum L.). The PR vs. WC relationships for two depths (0.21 and 0.27 m), below the level of cultivation, were similar to those at the 0.10‐m depth for the nontrafficked no‐till plots. These relationships for the 0.21‐ and 0.27‐m depths were not influenced by tillage, traffic, and corn cropping system treatments. The variable depth of plowing in tilled plots was found to influence the data consistency for the 0.21‐m depth, indicating the penetrometer's high sensitivity to the soil conditions.

Ground-Dwelling and Foliar Arthropods in Four Cropping Systems

Four different corn, soybean, and wheat cropping systems were established in small replicated plots and simultaneously in larger (4-hectare) unreplicated fields. Each system was subject to distinct tillage practices, fertility programs, and methods of pest control, based on methods currently in use on farms in the Mid-Atlantic region of the United States. Ground-dwelling arthropods (mostly Carabidae and spiders) were sampled during the fourth and sixth growing season after the establishment of the plots, and foliar insects (pest and beneficial) and pest damage were sampled on corn in the sixth growing season. Overall, beneficial arthropod populations were lowest and corn pest insect populations (especially Western corn rootworms, Diabrotica virgifera virgifera LeConte) were highest in the simplest, most intensively managed continuous corn system, which had annual use of soil insecticides. Generally ground-dwelling species were higher in soybeans than in corn, and in no-till than in deep-tilled crops. Growers wishing to enhance populations of beneficial insects should consider predominantly no-till cropping systems with several different crops in the rotation and minimal insecticide use. For both ground and foliar sampling, patterns of abundance among systems and crops in the small replicated plots generally followed those observed in the large fields, but numbers of spiders and carabids collected per pitfall trap were generally much higher in the large fields.

Profitability of Various Corn, Soybean, Wheat, and Alfalfa Cropping Systems

Producers are frequently most interested in economic comparisons of various cropping systems. We compared continuous corn (Zea mays L.) and continuous soybean [Glycine max (L.) Merr.] with 2-, 3-, and 5-year rotations, the latter two including wheat (Triticum aestivum L.) and alfalfa (Medicago sativa L.), using either chisel plow or no-tillage practices. Crop yield and returns to land and management were evaluated. Yields for continuous corn (C-C-C) were not different from those in rotation [corn-soybean (C-S), soybean-wheat/soybeancorn (S-W/S-C), or corn-soybean-alfalfa-alfalfa-alfalfa (C-S-A-A-A)] for either tillage practice, but rotated corn had lower nitrogen (N) inputs. Soybean yield in the 5-year rotation was greater than for continuous soybean (S-S-S) in 2001 for both tillage practices, but in 2000, a tillage by rotation interaction resulted from severe crusting in S-S-S that reduced stand density and lowered yield for the chisel plow treatment. Wheat and alfalfa yields were not affected by tillage practice. Using average annual crop prices, the 5-year rotation generated returns that were 100 and 158% higher than for C-S using either no-tillage or chisel practices. This study confirms that producers who incorporate alfalfa into their crop rotations can significantly increase returns to land and management. However, returns for the rotation including alfalfa are more realistic where a viable forage market exists.

Laboratory Calibration, In-Field Validation and Use of a Soil Penetrometer Measuring Cone Resistance and Water Content

Concurrent and coincident measure of penetrometer cone resistance (PR) and water content (WC) were optimized by hourly in-field validation of data from time domain transmissiometry (TDT) for WC and piezoelectric force sensor for PR. A piezoelectric force sensor coupled to a cone is followed by a helical wrapped TDT sensor on a single penetrometer shaft. Detailed laboratory calibrations, coupled with in-field validations, were important to assure the quality of data, which facilitated detailed analyses of PR and WC patterns. The piezoelectric sensor relied on a calibrated spring for the in-field validation. The calibration of the TDT sensor had three stages: a series of fluids of known dielectric constant; soil columns at known, variable water contents; and field soils at a range of ambient conditions. The penetrometer was used to study soil strength and WC behavior in time and space along 300-m plots. The treatments were conventional and no-till, each at two levels of traffic. The crop was corn (Zea mays L.), continuous and in rotation with soybean [Glycine max (L.) Merr.] and wheat (Triticum aestivum L.). The PR vs. WC relationships for two depths (0.21 and 0.27 m), below the level of cultivation, were similar to those at the 0.10-m depth for the nontrafficked no-till plots. These relationships for the 0.21- and 0.27-m depths were not influenced by tillage, traffic, and corn cropping system treatments. The variable depth of plowing in tilled plots was found to influence the data consistency for the 0.21-m depth, indicating the penetrometer's high sensitivity to the soil conditions.

Response of chickpea (Cicer arietinum) to seeding time and phosphorus and their after-effects on succeeding baby corn (Zea mays)

A field study conducted during 2005-07 on chickpea (Cicer arietinum L.)-baby corn (Zea mays L.) cropping system on sandy loam soil at New Delhi revealed that chickpea cv 'ICCV 96029' produced higher mean green- seed (chholia) yield (1.20 tlha) than 'ICCV 96030' (0.93 tlha). The maximum chholia production was recorded when the crop was sown on 7 October (1.31 Vha), and the least (0.82 Vha) when it was sown on 15 October. Appli- cation of 26.4 kg Plha recorded significantly more chholia production (1 .I5 tlha) than 13.2 kg Plha (1.09 tlha) and unfertilized crop (0.94 tlha). The performance of the succeeding baby corn was not influenced by chickpea culti- vars. Baby corn raised after chickpea sown on 15 October recorded higher yield than that after chickpea grown af- ter two other dates of seeding. Baby corn after chickpea fertilized with 26.4 kg Plha produced the highest yield. The chickpea-baby corn cropping system on an average removed 16.47 kg Plha, whereas the cropping system received 39.6 kg Plha, resulting in build-up of available soil P by 0.73 kglha. The net returns followed the trend of chholia production. Thus sowing chickpea cv 'ICCV 96029' on 7 October with 13.2 kglha for chholia with the suc- ceeding baby corn receiving the recommended dose of fertilizers is best for productivity and returns of chickpea- baby corn cropping system.

Integrated management of itchgrass in a corn cropping system: modeling the effect of control tactics

Abstract A population model of itchgrass was developed for a typical corn–based cropping system in the Pacific coastal region of Costa Rica. Field experiments were conducted to quantify density-dependent seedling mortality and fecundity. Additional information required for the model was obtained from the literature. Effect of control methods on itchgrass density—including a leguminous cover crop (velvetbean), a preemergence herbicide (pendimethalin), and classical biocontrol with the head smut—alone and in combination, were investigated using the model. According to model results, the cover crop planted at high and low densities between corn rows was highly efficient, reducing the initial itchgrass density from 54 plants m−2 to 4 and 17 plants m−2, respectively. Associating velvetbean with corn solely in the first crop each year resulted in predicted itchgrass densities of 33 and 36 plants m−2 (at high and low cover crop planting densities, respectively). The improvement in corn yield from preemergence he...

Cropping System Effects on Weed Emergence and Densities in Corn

The USDA has a goal of implementing integrated pest management (IPM) practices on 75% of the cropland in the USA so growers may adopt weed control practices that emphasize crop rotation and cultivation. Our objectives were to estimate weed densities in corn (Zea mays L.) and to examine weed emergence in an unmanaged weed area of corn following 4 yr of continuous corn, which received preemergence broadcast herbicides, and following soybean [Glycine max (L.) Merr.]–corn and soybean–wheat (Triticum aestivum L.)/red clover (Trifolium pratense L.)–corn cropping systems, which received banded herbicides and cultivation, on four farms in New York. More total weeds emerged at two sites and more perennial weeds emerged at all sites in the unmanaged weed area of corn in the soybean–wheat/red clover–corn cropping system compared with continuous corn because of poor red clover establishment, which resulted in a fallow period after wheat harvest. Weed densities in corn averaged 6.3 and 9.9 weeds m−2 in the soybean–wheat/red clover–corn cropping system, compared with 1.7 and 1.0 weeds m−2 in continuous corn at two of the sites, because of greater weed emergence and unsatisfactory weed control with banded herbicides and a single cultivation in the soybean–wheat/red clover–corn cropping system. When red clover does not establish well, growers should expect increased weed densities in the subsequent corn crop. Growers should then consider fall tillage or herbicide application after wheat harvest, or additional cultivation(s) or herbicide applications in the subsequent corn crop.

Evaluation and Comparison of Five Simulation Models for Estimating Water Drainage Fluxes under Corn

AbstractThe simulation accuracies of five water quality models, LEACHW, MACRO, NCSWAP, SLIM, and SOIL to predict the amount of drainage water were evaluated and compared to field data from a 5‐yr leaching experiment. The study was conducted on Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalf). Drainage fluxes below the rooting zone of corn were measured with pan lysimeters in 1988–1989, 1989–1990, 1990–1991, 1991–1992, and 1992–1993. A series of 18 zero‐tension pan lysimeters (0.465 m2 area) were installed at a depth of 1.2 m to collect drainage water at approximately the rooting depth of corn. All five models were calibrated to the site conditions using data from 1989 to 1990. The calibrated inputs were then used to evaluate the models' simulating accuracy using 1988–1989, 1990–1991, 1991–1992, and 1992–1993 drainage data. The cumulative annual simulations of drainage water from each model were compared to the mean of pan efficiency corrected measured data for these five sampling years. Simulated results for all five models fell within 95% confidence intervals of the measured data. Validation simulations of drainage fluxes were about as accurate as calibration simulations. The statistical analyses indicated that all five models performed well and have the potential to accurately predict the amount of drainage fluxes below the 1.2 m depth under corn cropping system without the need to calibrate the model for each year. There were small differences among the overall performances of the models for simulating drainage losses, but these differences were not significant using one‐way analysis of variance.

Increased weed emergence and seed bank depletion by soil disturbance in a no-tillage system

The influence of secondary soil disturbance on the emergence pattern and seed bank depletion of an annual weed community in a long-term, no-tillage corn cropping system was determined in 1992 and 1993. As a component of this research, the seed bank was characterized prior to implementation of soil disturbance treatments. The seed bank was initially composed of common lambsquarters, redroot pigweed, and giant foxtail, with approximately 55, 36, and 8% of the total viable seeds, respectively. The remaining 1% was comprised of five other species in 1992 and eight in 1993. The spatial distribution of viable seeds of each species, except common lambsquarters and redroot pigweed, was described by a negative binomial distribution. Three dispersion indices indicated that seeds of individual and total weed species were aggregated and that the level of aggregation of viable seeds of a species was associated with seed density; at lower seed densities, the level of aggregation was greater. Soil disturbance increased common lambsquarters emergence 6-fold in 1992 relative to nondisturbed soil, but did not influence emergence in 1993. Rainfall was about 50% less in 1993. In contrast, soil disturbance increased giant foxtail and redroot pigweed emergence approximately 6- and 3-fold in 1992 and 1993, respectively. Seedling emergence associated with soil disturbance, relative to nondisturbed soil, increased seed bank depletion of common lambsquarters 16-fold in 1992, and giant foxtail and redroot pigweed and average of 6- and 3-fold in 1992 and 1993, respectively. These results indicated that soil disturbance increased seedling emergence and seed bank depletion of the predominant species in the weed community of a long-term, no-tillage system, but that this response was dependent on rainfall for common lambsquarters.

Seed bank characterization and emergence of a weed community in a moldboard plow system

Field experiments were conducted in 1992 and 1993 to characterize the weed seed bank, to determine the influence of moldboard plowing and secondary soil disturbance on the emergence pattern of weeds, and to measure weed seed bank depletion by emergence in a long-term moldboard plow corn cropping system. Viable seeds of common lambsquarters, redroot pigweed, and each of 10 other species accounted for about 85, about 9, and less than 1%, respectively, of the total weed species in the seed bank. A negative binomial distribution described the spatial distribution of viable seeds of 10 species, but not of common lambsquarters or of redroot pigweed. Decreased density of seeds among species was associated with increased aggregation. Secondary soil disturbance increased the rate and magnitude of common lambs quarters emergence in 1992 but did not influence emergence in 1993. Secondary soil disturbance did not influence the magnitude and rate of emergence of redroot pigweed or velvetleaf. Whereas cumulative growing degree days from April through July were similar between years, the amount of rainfall was about 50% less in 1992 than in 1993. Secondary soil disturbance may have increased common lambsquarters emergence by increasing the availability of soil moisture and improving conditions for seed germination during the dry year. Even though seed bank depletion by seedling emergence was relatively low for all species, secondary soil disturbance in creased seed bank depletion of common lambsquarters and redroot pigweed about 7- and 3-fold, respectively, in 1992. Seasonal variation in the amount of rainfall may have influenced the effect of soil disturbance on emergence and seed bank depletion of common lambsquarters, which is the most abundant species in the weed community.

Chlorophyll Meter and Stalk Nitrate Techniques as Complementary Indices for Residual Nitrogen

Improved N management techniques are needed to prevent excess N applications while maintaining yields. Environmentally, development of these improved techniques has become critical for crops such as irrigated corn (Zea mays L.), which require large N fertilizer inputs to maximize yield. Our objective was to determine if some current N management techniques could be used to guide and improve future soil sampling strategies that would result in improved N fertilizer recommendations and reduced adverse environmental effects. Chlorophyll meter readings and end-of-season stalk nitrate-N concentrations were taken from an irrigated corn study at Shelton, NE, from 1992 through 1994. Residual soil N samples were collected to a depth of 5 ft after the 1992 and 1993 growing seasons. This study included continuous corn and soybean [Glycine max (L.) Merr.]- corn rotations with four corn hybrids and five N fertilizer rates. Chlorophyll meter readings taken at several growth stages reached a maximum at sufficient N levels for maximum yield and then plateaued. Similarly, end-of-season stalk nitrate-N concentrations exceeded established thresholds (-2000 ppm) above the N fertilizer rate where maximum yields were obtained in both cropping systems. Together, these techniques provided additional criteria to help partition and separate fields into areas with potentially different levels of residual soil N. This information can then be used to guide soil sampling and to develop or improve site specific N fertilizer recommendations which should decrease environmental risk by reducing the amount of nitrate-N available for leaching.

Comparison of Measured and WEPP Predicted Runoff and Soil Loss for Midwest Claypan Soil

Runoff and soil loss predictions from the Water Erosion Prediction Project (WEPP) Hillslope model were compared to measured losses from continuous cultivated fallow and continuous corn and soybean cropping systems under conventional, chisel, and no-till tillage methods. Runoff and soil loss data were collected over an 11-yr period (1983-1993) from the study plots on Mexico claypan soil near Kingdom City, Missouri. For all treatments, the model predicted runoff and soil loss reasonably well for the wet years with annual runoff >200 mm but greatly underpredicted for the dry years with annual runoff <100 mm. During the dry seasons, most of the rainfall events occurred after a long dry period and the model overestimated runoff from several events when little or no runoff was measured. When averaged by tillage treatment, mean annual runoff predictions for continuous corn and continuous soybean were within 15% of those measured. The model overpredicted soil losses from continuous corn and continuous soybean by 22 and 87%, respectively. Both measured and predicted runoff and soil losses from continuous soybean were higher than from continuous corn. When averaged over crop, the model slightly overpredicted mean annual runoff for conventional, chisel, and no-till systems. The model did not show appreciable difference in annual runoff prediction for the different tillage systems. Predicted soil losses for conventional, chisel, and no-till tillage systems were 50, 67, and 29% higher, respectively, than those measured. Runoff and soil loss data were also analyzed by cropstage periods. A tillage year was divided into rough fallow (F), seedbed (SB), rapid growth (P12), reproduction and maturation (P3), and residue (P4) periods. Runoff predictions for the F and SB periods were reasonable. The model overpredicted runoff for the P12 and P3 periods and underpredicted for the P4 period. The model overpredicted soil loss from all periods except for the F period. For continuous corn and soybean cropping systems, more than 50% of the total measured and predicted tillage year soil loss occurred during the SB period. The model was also tested for seven large events that occurred during the study period. Predicted runoff and soil loss for these events compared well to those measured.

Giant Foxtail (Setaria faberi) Resistance to Aryloxyphenoxypropionate and Cyclohexanedione Herbicides

A giant foxtail (PCW1) population putatively resistant to fluazifop-P and sethoxydim was identified in a carrot, onion, and corn cropping system in Wisconsin during 1991. Previous, extensive use of fluazifop and fluazifop-P over several years imposed a high level of selection intensity on grass weeds. In a field experiment, fluazifop-P, sethoxydim, and quizalofop at recommended dosages resulted in 58, 53, and 45% plant survival, respectively, within the PCW1 giant foxtail population; no plants survived treatment with clethodim or nicosulfuron, and few plants survived treatment with imazethapyr at recommended dosages. Based on shoot dry biomass reduction in greenhouse experiments, a PCW1 giant foxtail biotype had 16-, &gt; 9-, 4.9-, and 4.2-fold resistance to fluazifop-P, diclofop, quizalofop, and fenoxaprop, respectively, relative to a giant foxtail (AC1) accession that was susceptible to aryloxyphenoxypropionate (APP) and cyclohexanedione (CHD) herbicides. The PCW1 biotype had 134-fold resistance to sethoxydim and slight and inconsistent resistance to clethodim. The PCW1 biotype and AC1 accession were equally susceptible to imazethapyr, linuron, and oxyfluorfen. Based on plant survival, a PCW1 giant foxtail accession had 25- and &gt; 143-fold resistance to fluazifop-P and sethoxydim, respectively, relative to the AC1 accession. The selection intensity associated with repeated use of fluazifop and fluazifop-P over 5 yr contributed to the cross-resistance of PCW1 giant foxtail to APP and CHD herbicides.

The effect of forty years of continuous corn cropping on soil organic matter characteristics

Changes in humus and some of the major extractable components of soil organic matter were examined, following forty years of conventionally tilled continuous corn cropping compared with those of an adjacent untilled native grassland soil. Results indicate that long-term continuous cropping caused a significant reduction in the content of alkali extractable and water soluble carbon, as well as in the phenolic and chloroform extractable compounds, while no differences in volatile acids and n-hexane extractable substances were found. On the basis of organic C, corn cropping led to a relative enrichement of phenolic compounds, volatile acids and substances extractable by Na4P2O7, but it did not affect the substances extractable by water. Except for the humification ratio (HR), the humification parameters, such as humification degree (HD), the extracted humic and fulvic acids, the CHA/CFA ratio and the humification index (HI) revealed a higher degree of humification of the organic matter in native grassland than in the continuous corn cropping system. IR spectra of n-hexane, chloroform, alkaline and water extracts failed to show significant differences between sites under native grassland and sites under continuous corn.

Potassium in Two Humid Tropical Ultisols under a Corn and Soybean Cropping System: II. Dynamics

AbstractUnderstanding the dynamics of soil K is important for the formulation of a sound fertilizer management strategy. Two experiments were conducted to determine the behavior of K in the soil after fertilization. Five rates of K (0 to 120 kg ha−1) were applied to two Typic Paleudults, a loam and a sandy loam, in the Peruvian Amazon Basin. A three‐crop rotation of corn (Zeu mays L.), corn, and soybean [Glycine max (L.) Merr.] was planted at each site. Three additional crops of corn were grown at the loam site. Potassium rates were applied only to the first crop of each three‐crop cycle. The corn stover was returned, while the soybean stover was removed. Soil samples were taken at germination, flowering, and harvest of each crop at 20‐cm depth intervals to 60 cm in the loam and 80 em in the sandy loam. Soil K was extracted with NaHCO3, NH4OAc, and concentrated H2SO4. Topsoil exchangeable K increased markedly with K addition, either as fertilizer or as stover, but rapidly decreased during cropping. Changes in the exchangeable pool were characterized with an exponential model. Increases in exchangeable K below 20 cm were of minor significance for the loam. For the sandy loam, however, subsoil exchangeable K was significantly increased to 60 cm. Evidences of K fixation and release were detected in the loam where the topsoil non‐exchangeable pool peaked after K additions and decreased during cropping. There was no evidence of fixation in the sandy loam. These differences suggest that higher K rates can be applied to the finer textured soils and there is less risk of loss of K from the rooting zone.

Potassium in Two Humid Tropical Ultisols under a Corn and Soybean Cropping System: I. Management

AbstractSub‐optimum soil K levels often limit corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production in humid tropical Ultisols. The objectives of this study were to determine soil and plant critical levels of K and optimum rates of K fertilization for corn and soybean grown in the Amazon Basin of Peru. Two field experiments were conducted on Typic Paleudults, a loam and a sandy loam. Five K rates, ranging from 0 to 120 kg ha−1, were broadcast and incorporated prior to planting the first crop of a corn, corn, soybean rotation at both sites. At the loam site, K treatments were reapplied at the end of this rotation and three more corn crops grown. The corn stover was returned while the soybean stover was removed. Critical exchangeable K levels for corn were 110 kg ha−1 on the loam and 90 kg ha−1 on the sandy loam, while for soybean it was 75 kg ha−1 for both soils. The critical levels of K in plant tissue at flowering were 13 g kg−1 in corn and 12 g kg−1 in soybean. Soybean seemed to lower exchangeable K to where K was released from non‐exchangeable sources. An annual cropping system of corn and soybean with an intervening cover crop during the rainy season is proposed for the region. Potassium fertilization is recommended only prior to growing corn at 90 kg ha−1 on a loam and 60 kg ha−1 on a sandy loam.

Intercropping corn and soybean for silage in a cool-temperature region: Yield, protein and economic effects

Corn (Zea mays L.) and soybean (Glycine max[L.] Merr.) were intercropped for silage in 1985 and 1986 at the Central Experimental Farm, Ottawa, Canada to evaluate silage yield, protein and economic effects. In both years, a complete 2 × 2 ×3 factorial was analysed for two corn hybrids (dwarf and tall), two corn cropping systems (monocropped and intercropped), and three N fertilizer levels (0, 60 and 120 kg N ha−1). In addition to the complete factorial treatments, monocropped soybeans with 0 kg N ha−1 and an intercrop treatment of dwarf and tall corn at 120 kg N ha−1 were grown. In 1986, four population-density levels of the intercropped tall corn and soybean, at 60 kg N ha−1, were also compared.Total yields averaged over corn hybrids and cropping systems had a quadratic response, increasing from 0 to 60 kg N ha−1 and then decreasing slightly between 60 and 120 kg N ha−1, in both years. Monocrops of corn yielded significantly more in both years than intercrops, except tall-corn intercrops in 1986 grown at monocropped-corn population densities. Both corn and soybean of the dwarf-corn intercrops in the dry year of 1985 had a consistent trend of lower dry-matter and protein yields than in tall-corn intercrops at the same levels of N. These differences did not consistently favour either corn hybrid in 1986.The concentration of crude protein was significantly higher in intercropped than monocropped silage in both years. In 1986, this was also true for the protein yield ha−1. Increasing N application resulted in higher total silage protein concentrations in both years. The total silage protein concentration was, on average, 1.53 and 2.15 percentage points higher in intercrops than in the corresponding monocropped corn hybrid at the same level of N in 1985 and 1986, respectively. The total silage protein concentrations in both years and the protein yield in 1986 were greater for tall corn than for dwarf corn.All treatments at 0 kg N ha−1, the dwarf-corn intercrops in 1985 and monocropped dwarf corn at 120 kg N ha−1 in both years, were less cost-effective than the standard, monocropped tall corn at 120 kg N ha−1. In 1985, the tall corn intercrop at 60 kg N ha−1 had a $135 ha−1 cost-effective advantage over the standard treatment. In 1986, this intercrop had a $132 ha−1 advantage, which was improved to $261 ha−1 when the corn population was maintained at monocrop levels and the population of soybeans was reduced by 50%. Land equivalent ratios (lers) based on dry-matter weights ranged from 0.97 to 1.11 in dwarf-corn intercrops and from 1.16 to 1.23 in tall-corn intercrops in 1985. The ler range in 1986 was from 1.11 to 1.12 in dwarf-corn intercrops, and from 1.04 to 1.23 in tall-corn intercrops.

Reduction of European Corn Borer (Lepidoptera: Pyralidae) Damage by Intercropping Corn with Soybean

Corn, Zea mays L., and soybean, Glycine max (L.) Merrill, were intercropped for silage in 1985 and 1986 at the Central Experimental Farm, Ottawa, to determine effects on yields and the percentage of European corn borer, Ostrinia nubilalis Hubner, infestation. A 2 × 2 × 3 factorial was analyzed with two corn hybrids (dwarf PAG 391134 and tall Coop 5259), two corn cropping systems (monocropped and intercropped), and three nitrogen fertilizer levels (0, 60, and 120 kg N/ha). Intercropping significantly reduced European corn borer infestation in tall corn in 1985 and in both corn hybrids in 1986. Dwarf corn was infested significantly less than tall corn in both years and in both cropping systems. The commonly applied rate of 120 kg N/ha resulted in the highest European corn borer infestation. Yields and land equivalent ratios at 60 kg N/ha were as high as those at 120 kg N/ha, but European corn borer infestation was significantly less at 60 kg N/ha. Application of 0 kg N/ha resulted in the lowest yields and land equivalent ratios, but European corn borer infestation was not different from levels at 60 kg N/ha.

Time Series Analysis for Statistical Inferences in Tillage Experiments

AbstractSpatial dependence of soil physical properties often invalidates parametric inferencing of tillage treatment effects. Spectral analysis was examined as a possible means to generate inferences on tillage treatments from an observation set that is spatially dependent. The method was tested using surface elevation data from a long‐term tillage study. Three tillage treatments were imposed on a continuous corn cropping system in a randomized complete block design beginning in 1962. Surface elevations were measured in 1971, 1976, 1980, and 1987 along four transects oriented perpendicular to the imposed treatments with each transect running the length of the field. The power spectrum from the 1971 observations yielded a significant spectral peak at a wavelength equal to one‐plot width. The power spectra from the 1976, 1980, and 1987 observations yielded a significant spectral valley at a wavelength equal to one‐plot width. The significant spectral valleys in the 1976, 1980, and 1987 power spectra represent low variance within the plot spacing as compared to variance between plots. In a randomized complete block design, this significant spectral valley represents an inference on the effect of tillage on surface elevation using spectral analysis. Calculation of number of observations needed to show significant spectral differences at wavelength equal to one‐plot width compared to within and beyond plot wavelengths indicate that 75, 161, 223, and 149 observations were necessary for 1971, 1976, 1980, and 1987 sampling dates, respectively.