Corn and soybean grain yield responses to soil amendments and cover crop in upland soils

A field study was conducted on upland soils for six years to determine interactive effects of winter wheat (Triticum aestivum L.) cover crop, organic and inorganic soil amendments on grain yields and nutrient utilizations in a no-till corn (Zea mays)-soybean (Glycine max) rotation. Experimental design was a split-plot arrangement with four replicates. Cover crops were the main plots and fertilization treatments used as sub-plot. Fertilization treatments included an unfertilized control, poultry litter, poultry litter (PL) plus flue gas desulfurization (FGD) gypsum and inorganic N fertilizer applied every other year to corn. Corn grain yield and grain N and P uptake were greater with PL than inorganic fertilizer in 2014 and 2016. Addition of FGD gypsum to PL significantly increased corn grain yield by 15% in 2016. Cover crop increased corn and soybean grain yields in a year with less seasonal rainfall possibly by conserving soil moisture.     

Improving Soybean Performance in the Northern Great Plains through the Use of Cover Crops

Cover crops are capable of providing multiple benefits for improving soil quality and enhancing annual crop growth. Maintaining continuous plant cover on agricultural fields with cover crop is of great interest to improve nutrient cycling, prevent soil degradation, and promote further adoption of no-till farming systems. A field study was conducted in eastern South Dakota, USA, in 2007, 2008, and 2009 to evaluate four cover crop combinations [(1) no cover; (2) buckwheat (BUCK) (Fagopyrum esculentum Moench) + slender wheatgrass (Agropyron caninum L.) (SLD WHT); (3) oilseed radish (Raphanus sativus L.) (RAD) + SLD WHT; and (4) purple top turnips (Brassica rapa L.) (TURN + SLD WHT)] sown after oat (Avena sativa L.) on soybean [Glycine max (L.) Merr.] performance. The impacts of no tillage (NT) and conventional tillage (CT) were evaluated at two different planting populations. Soybean plant biomass, seed harvest index, yield, total nitrogen (N), oil concentration, and test weight were measured. Cover crops preceding soybean did not negatively impact most measured plant parameters. Seed yield was increased by the RAD + SLD WHT and TURN + SLD WHT in 2008, whereas in 2007 and 2009 no yield increase or slight yield decrease was shown by the cover crops. Soil tillage practice and planting population had a strong influence on seed yield and seed quality in all three study years.     

Influence of cover crops on potential nitrogen availability to succeeding crops in a Southern Piedmont soil

Winter cover crops are essential in conservation tillage systems to protect soils from erosion and for improving soil productivity. Black oat (Avena strigosa Schreb) and oilseed radish (Raphanus sativus L.) could be useful cover crops in the southeastern USA, but successful adoption requires understanding their influence on N availability in conservation tillage systems. Black oat and oilseed radish were compared to crimson clover (Trifolium incarnatum L.) and rye (Secale cereale L.) for biomass production and effects on N mineralization during the summer crop growing season from fall 1998 through summer 2002 near Watkinsville, GA. Rye produced 40 to 60% more biomass, although N contents were less than the other cover crops. Oilseed radish and black oat N contents were similar to crimson clover. Black oat, oilseed radish, and crimson clover C/N ratios were less than 30, whereas rye averaged 39. Amount of N mineralized in 90 days (N _min90) measured with in situ soil cores was 1.3 to 2.2 times greater following black oat, crimson clover, and oilseed radish than following rye. No differences in N _min90 were found between black oats, crimson clover, and oilseed radish in 1999 and 2000. The amount of potentially mineralizable N (N ₀) was not different due to cover crop, but was 1.5 times greater in 2000 and 2002 than in 1999. The rate of N mineralization (k) was 20 to 50% slower following rye than the other three cover crops. Black oat and oilseed radish biomass production and soil N mineralization dynamics were more similar to crimson clover than to rye, which indicates that they could be used as cover crops in the southeast without significant changes in N recommendations for most crops.

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WINTER CROPS AS BIOASSAYS OF SOIL NITROGEN-SUPPLYING CAPACITY

Soil nitrogen (N)-supplying capacity bioassays could present alternatives to traditional soil tests. Objectives were to identify winter crops and associated characteristics with bioassay potential. Saint Joseph and Bossier City, LA experiments used randomized complete block designs with factorial N fertilizer and winter crop treatment arrangements. Nitrogen rates were applied to corn (Zea mays L.) in 2004. Unfertilized winter wheat ( Triticum aestivum L.), cereal rye (Secale cereale L.), native winter vegetation, and weed-free winter fallow treatments followed corn. At Saint Joseph, cotton (Gossypium hirsutum L.) followed winter crop treatments. Greater corn N rate consistently increased winter crop biomass and N accumulation, suggesting potential as bioassays, and increased Saint Joseph seedcotton yield. Winter crop-seedcotton yield N-response relationships were non-significant by familywise error rate criteria. However, some winter crop characteristics, such as rye N accumulation, for which a relationship to seedcotton yield closely approached significance, may merit further research as soil N-supplying capacity bioassays.     

Arbuscular mycorrhizal fungi and soil aggregation in a no‐tillage system with crop rotation

Crop rotation adoption in no‐tillage systems (NTS) has been recommended to increase the biological activity and soil aggregation, suppress soil and plant pathogens, and increase the productivity aiming at the sustainability of agricultural areas. In this context, this study aimed to assess the effect of crop rotation on the arbuscular mycorrhizal fungi (AMF) community and soil aggregation in a soil cultivated for nine years under NTS. Treatments consisted of combinations of three summer crop sequences and seven winter crops. Summer crop sequences consisted of corn (Zea mays L.) monoculture, soybean (Glycine max L. Merrill) monoculture, and soybean–corn rotation. Winter crops consisted of corn, sorghum (Sorghum bicolor (L.) Moench), sunflower (Helianthus annuus L.), sunn hemp (Crotalaria juncea L.), pigeon pea (Cajanus cajan (L.) Millsp.), oilseed radish (Raphanus sativus L.), and millet (Pennisetum americanum (L.) Leeke). Soil samples were collected at a depth of 0–0.10 m for analyses of soil chemical, physical, and biological attributes. Spore abundance, total glomalin, and soil aggregate stability index were higher in the soil under corn monoculture. The highest values of aggregate mean weight diameter were observed in the soybean–corn rotation (3.78 mm) and corn monoculture (3.70 mm), both differing from soybean monoculture (3.15 mm), while winter crops showed significant differences only between sorghum (3.96 mm) and pigeon pea (3.25 mm). Two processes were identified in the soil under summer crop sequences. The first process was observed in PC1 (spore abundance, total glomalin, easily extractable glomalin, pH, P, and Mg²⁺) and was related to AMF; the second process occurred in PC2 (aggregate mean weight diameter, soil aggregate stability index, K⁺, and organic matter) and was related to soil aggregation. The nine‐year no‐tillage system under the same crop rotation adoption influenced AMF abundance in the soil, especially with corn cultivation in the summer crop sequence, which promoted an increased total external mycelium length and number of spores of AMF. In addition, it favored an increased soil organic matter content, which is directly related to the formation and stability of soil aggregates in these managements.     

Sustaining Soil Quality with Legumes in No‐Tillage Systems

Abstract

Tillage, cropping system, and cover crops have seasonal and long‐term effects on the nitrogen (N) cycle and total soil organic carbon (C), which in turn affects soil quality. This study evaluated the effects of crop, cover crop, and tillage practices on inorganic N levels and total soil N, the timing of inorganic N release from hairy vetch and soybean, and the capacity for C sequestration. Cropping systems included continuous corn (Zea mays L.) and stalk residue, continuous corn and hairy vetch (Vicia villosa Roth), continuous soybeans (Glycine max L.) plus residue, and two corn/soybean rotations in corn alternate years with hairy vetch and ammonium nitrate (0, 85, and 170 kg N ha^?1). Subplot treatments were moldboard plow and no tillage. Legumes coupled with no tillage reduced the N fertilizer requirement of corn, increased plant‐available N, and augmented total soil C and N stores.     

Winter cover cropping influence on nitrogen mineralization,presidedress soil nitrate test,and corn yields

The mineralization and availability of cover crop N to the succeeding crop are critical components in the management of soil N to reduce N leaching. The effects of several leguminous and non-leguminous cover crops on soil N availability, N mineralization potential, and corn (Zea mays L.) yield were examined. The cover crops had variable effects on soil N availability and corn yield and N uptake. Because of the rapid mineralization of the cover crops following incorporation, the inorganic N levels in the soil sampled in mid-May 1992 (4 weeks after incorporation of cover crops), rather than the potentially mineralizable N, rate constants, initial potential mineralization rate, or cumulative N mineralized over 14 weeks, correlated well with N concentrations, C:N ratios, or the N added in the cover crops. However, the inclusion of potentially mineralizable N with inorganic N in a multiple regression improved the variability in the corn yield and the N uptake accounted for. Since extensive mineralization had occurred before the 21 May sampling, the potentially mineralizable N was affected more by the soil organic N and C than by the N concentrations of the cover crops. The presidedress NO₃ ^--N test levels were well predicted by the inorganic and potentially mineralizable N (R ²=0.89, P<0.01), although the test levels were better in predicting corn yield and N uptake. If the available soil N test needs to be made earlier than recommended by the presidedress NO₃ ^--N test, both inorganic and potentially mineralizable N are needed to better predict the corn yield and N uptake in the soils.     

Cover‐crop seeding‐date influence on fall nitrogen recovery

Planting cover crops after corn‐silage harvest could have a critical role in the recovery of residual N and N from fall‐applied manure, which would otherwise be lost to the environment. Experiments were conducted at the University of Massachusetts Research Farm during the 2004–2006 growing seasons. Treatments consisted of oat and winter rye cover crops, and no cover crop, and four cover‐crop dates of planting. The earliest planting dates of oat and winter rye produced the maximum biomass yield and resulted in the highest nitrate accumulation in both cover‐crop species. The average nitrate accumulation for the 3 years in winter rye and oat at the earliest time of planting was 60 and 48 kg ha^–1, respectively. In 2004 where the residual N level was high, winter rye accumulated 119 kg nitrate ha^–1. While initially soil N levels were relatively high in early September they were almost zero at all sampling depths in all plots with and without cover crops later in the fall before the ground was frozen. However, in plots with cover crops, nitrate was accumulated in the cover‐crop tissue, whereas in plots with no cover crop the nitrate was lost to the environment mainly through leaching. The seeding date of cover crops influenced the contribution of N available to the subsequent crop. Corn plants with no added fertilizer, yielded 41% and 34% more silage when planted after oat and rye, respectively, compared with the no–cover crop treatment. Corn‐silage yield decreased linearly when planting of cover crops was delayed from early September to early or mid‐October. Corn‐ear yield was influenced more than silage by the species of cover crop and planting date. Similar to corn silage, ear yield was higher when corn was planted after oat. This could be attributed in part to the winter‐kill of oat, giving it more time to decompose in the soil and subsequent greater release of N, while the rapidly increasing C : N ratio of rye can lessen availability to corn plants. Early plantings of cover crops increased corn‐ear yield up to 59% compared with corn‐ear yield planted after no cover crop.     

Cover crop nitrogen availability to conventional and no‐till corn: Soil mineral nitrogen,corn nitrogen status,and corn yield

Abstract

Understanding seasonal soil nitrogen (N) availability patterns is necessary to assess corn (Zea mays L.) N needs following winter cover cropping. Therefore, a field study was initiated to track N availability for corn in conventional and no‐till systems and to determine the accuracy of several methods for assessing and predicting N availability for corn grown in cover crop systems. The experimental design was a systematic split‐split plot with fallow, hairy vetch (Vicia villosa Roth), rye (Secale cereale L.), wheat (Triticum aestivum L.), rye+hairy vetch, and wheat+hairy vetch established as main plots and managed for conventional till and no‐till corn (split plots) to provide a range of soil N availability. The split‐split plot treatment was sidedressed with fertilizer N to give five N rates ranging from 0–300 kg N ha^‐1 in 75 kg N ha^‐1 increments. Soil and corn were sampled throughout the growing season in the 0 kg N ha^‐1 check plots and corn grain yields were determined in all plots. Plant‐available N was greater following cover crops that contained hairy vetch, but tillage had no consistent affect on N availability. Corn grain yields were higher following hairy vetch with or without supplemental fertilizer N and averaged 11.6 Mg ha^‐1 and 9.9 Mg ha^‐1 following cover crops with and without hairy vetch, respectively. All cover crop by tillage treatment combinations responded to fertilizer N rate both years, but the presence of hairy vetch seldom reduced predicted fertilizer N need. Instead, hairy vetch in monoculture or biculture seemed to add to corn yield potential by an average of about 1.7 Mg ha^‐1 (averaged over fertilizer N rates). Cover crop N contributions to corn varied considerably, likely due to cover crop N content and C:N ratio, residue management, climate, soil type, and the method used to assess and assign an N credit. The pre‐sidedress soil nitrate test (PSNT) accurately predicted fertilizer N responsive and N nonresponsive cover crop‐corn systems, but inorganic soil N concentrations within the PSNT critical inorganic soil N concentration range were not detected in this study.     

Organically grown Brassica napus – use of border strips and Trichoderma

Oilseed rape (Brassica napus L.) is a very difficult crop to cultivate organically. Only few organic methods are effective in reducing damage from insects and diseases. The current investigation assessed the use of the beneficial ascomycete Trichoderma asperellum (Samuels, Lieckf & Nirenberg) and a trap crop of Brassica rapa L. turnip rape cv. “Brachina,” both with and without an application of slurry fertilizer, for pest suppression and yield enhancement of winter oilseed rape cv. “Californium.” The presence of the trap crop significantly increased 1000 grain weight but not total yield or lipid content of the oilseed rape because turnip rape was not attractive enough to prevent colonization of the principal crop. Increase in 1000 grain weight, lipid content, and total seed yield were found in oilseed rape sprayed with three applications of T. asperellum, but the ascomycete had no influence on the insect pests observed. The effects of the fertilizer are about equal to the effects of the fungus on 1000 grain weight and on lipid content.     

Early season nitrogen accumulation in winter wheat

Cereal rye (Secale cereale L.) is widely used as a winter cover crop to conserve soil residual nitrogen (N) in the mid‐Atlantic region of the United States. Cereal rye, however, has agronomic drawbacks that may make other winter small grain crops more desirable alternatives. Winter wheat (Triticum aestivum L.) is a small grain that could substitute for cereal rye as a cover crop because it would give growers the flexibility of using it as a cover crop or growing it to maturity. There is currently little information on early season N accumulation of winter wheat cultivars, which is critical for the success of a small grain cover crop. To determine the degree of variation in early season N accumulation and early season biomass yield in soft red winter wheat in the mid‐Atlantic region, twenty‐five commercially available cultivars were evaluated at Beltsville, MD in the 1996/1997 and 1997/1998 growing seasons. Acereal rye cultivar ("Wheeler") was included as a cover crop control. Samples of plant tissue were taken at Feekes growth stage 5 and at physiological maturity each year. There were significant differences among cultivars for early season N accumulation and biomass yield. A large group of wheat cultivars had similar early season N accumulation and biomass yield as the cereal rye cover crop control. This suggests that some cultivars of winter wheat may be as effective as cereal rye as a winter cover crop. Early season N accumulation was highly correlated (r=0.90***) with early season biomass yield rather than with plant N content. These results indicate that soft red winter wheat has potential as a dual grain and cover crop and could be considered an alternative to cereal rye as a winter cover crop for conserving residual soil nitrogen in the mid‐Atlantic region of the United States.     

Notice

Abstract

Interest is increasing in alternative, reduced input cropping systems. Potential interactive effects of input additions or eliminations on crop yield must be delineated to develop the most resource‐efficient cropping systems. Information of this type is especially lacking in the southern United States. The principal objective of this field study was to determine the main and interactive effects of nitrogen (N) fertilization, herbicide, and insecticide on grain yields in a corn (Zea mays L.)‐soybean [(Glycine max (L.) Merr.)] rotation. Dryland studies were conducted for four years (1990–1993) on a Weswood silt loam soil (fine, mixed, thermic Fluventic Ustochrept). Variables included none or “optimal”; applications of N fertilizer, herbicide, and insecticide. Mean corn grain yield was increased 156% by N fertilization compared to the no N control. Herbicide significantly increased corn grain yield two of four years, while soil‐applied insecticide had no effect. Johnsongrass [Sorghum halepense (L.) Pers.] was identified as the primary competitive weed species in corn. No interactions of inputs were observed for corn grain yield. Nitrogen fertilization and herbicide did not affect soybean yield, but insecticide increased average soybean yield by 29%. Interactions of N fertilization and insecticide and herbicide and insecticide were significant for soybean yield.     

Corn Yield and Nitrogen- and Water-Use under No-Tillage Rotations

Increased crop diversity and length of rotation may improve corn (Zea mays L.) yield and water- and nitrogen-use efficiency (WUE and NUE). The objectives of this study were to determine effects of crop rotation on corn yield, water use, and nitrogen (N) use. No-tillage (NT) crop rotations were started in 1997 on a Barnes clay loam (fine-loamy, mixed, superactive, frigid Calcic Hapludoll) near Brookings, S.D. Rotations were continuous corn (CC), corn–soybean [Glycine max (L.) Merr.] (CS), a 3-year rotation of corn–soybean–oat/pea (Avena sativa L. and Pisum sativum L.) hay (CSH), a 3-year rotation of corn–soybean–spring wheat (Triticum aestivum L.) (CSW), and a 5-year rotation of corn–soybean–oat/pea hay companion seeded with alfalfa (Medicago sativa L.)–alfalfa–alfalfa (CSHAA). Fertilizer N was applied to corn on all rotations at planting (16 kg N ha^?1) and side-dressed (64 kg N ha^?1). Average corn grain yields (1998–2007) were greatest under CSW (7.38 Mg ha^?1) and least under CC (4.66 Mg ha^?1). Yields were not different among CSH, CSW, and CSHAA rotations. Water-use efficiency of rotation was ordered as CSW > CSH > CSHAA > CS > CC. Nitrogen-use efficiency was greatest under CSW and least under CC. There were no differences in yield advantage (YA) among crop rotations during years with plentiful early-season rainfall (May 1–July 31). In years with low spring rainfall, YA was greatest under CSW (54%) and least under CSHAA (33%). Corn yields under extended rotations (CSH, CSW, and CSHAA) were greater than under CC and CS, but lack of rainfall may result in reduced yields under CSHAA.     

Role of Cover Crops and Planting Dates for Improved Weed Suppression and Nitrogen Recovery in No till Systems

ABSTRACT

Cover crops improve the recovery and recycling of nitrogen and impart weed suppression in crop production. A two-year study with six weekly plantings of cover crops including non-winterkilled species (hairy vetch, Vicia villosa L.; winter rye Secale cereale L.) and winterkilled species (oat, Avena sativa L.; forage radish, Raphanus sativus L.) were assessed for effects on growth of forage rape (Brassica napus L.) and weed suppression. Early planting of cover crops gave the highest biomass and highest nitrogen accumulation. Delaying planting from early-September to mid-October suppressed cover-crop biomass by about 40%. Forage radish produced more biomass in the fall than other cover crops but was winter killed. Spring biomass was highest with rye or vetch. All cover crops suppressed weeds, but suppression was greatest under rye or hairy vetch. Hairy vetch accumulated the largest nitrogen content. Forage rape plants yielded more biomass after a cover crop than after no-cover crop.     

Soil carbon as affected by cover crops under no‐till under tropical climate

In tropical, low‐fertility soils, crop yields are dependent on soil carbon, and cropping systems under no‐till can increase soil C stocks. Plant residues supplied by cover crops in no‐till systems may improve aggregate stability and soil carbon, which may be further increased with the introduction of a legume in the cropping system. This research studied the effects of cover crops in rotation with soybean under no‐till on soil carbon and nitrogen, in Botucatu, Brazil, for 3 yr. The cover crops were millet (Penninsetum americanum Leek), cober crop (Sorghum bicolor × Sorghum sudanense) and sunn hemp (Crotalaria juncea L.), grown in the spring. Fallow without cover crops was used as a control. Grain sorghum (Sorghum bicolor L. Moench) and soybean (Glycine max (L.) Merril) were grown in fall–winter and summer, respectively. Generally, cover crops increased soil carbon contents, but soil N was only increased by sunn hemp in the particulate organic C fraction. An increase in the labile carbon fraction in the topsoil layers was closely related to cover crop root development. Fallow in spring should not be recommended in degraded soils with lowcarbon stock. Labile‐fractioned soil organic carbon and total carbon levels are more efficiently increased by grasses than by legumes in the short term, and grasses cropped in spring increase soil C/N ratio. Conversely, the introduction of a legume (sunn hemp) maintained a more stable C/N ratio, that is around 10, which would be more effective in increasing soil C in the long term.     

Compost,Manure and Synthetic Fertilizer Influences Crop Yields,Soil Properties,Nitrate Leaching and Crop Nutrient Content

From 1993 to 2001, a maize-vegetable-wheat rotation was compared using either 1) composts, 2) manure, or 3) synthetic fertilizer for nitrogen nutrient input. From 1993 to 1998, red clover (Trifolium pratense L.) and crimson clover (Trifolium incarnatum L.) were used as an annual winter legume cover crop prior to maize production. From 1999 to 2001, hairy vetch (Vicia villosa Roth.) served as the legume green manure nitrogen (N) source for maize. In this rotation, wheat depended entirely on residual N that remained in the soil after maize and vegetable (pepper and potato) production. Vegetables received either compost, manure, or fertilizer N inputs. Raw dairy manure stimulated the highest overall maize yields of 7,395 kg/ha (approximately 140 bushels per acre). This exceeded the Berks County mean yield of about 107 bushels per acre from 1994 to 2001. When hairy vetch replaced clover as the winter green manure cover crop, maize yields rose in three of the four treatments (approximately 500-1,300 kg/ha, or 10-24 bu/a). Hairy vetch cover cropping also resulted in a 9-25 % increase in wheat yields in the compost treatments compared to clover cover cropping. Hairy vetch cover crops increased both maize and wheat grain protein contents about 16 to 20% compared to the clover cover crop. Compost was superior to conventional synthetic fertilizer and raw dairy manure in 1) building soil nutrient levels, 2) providing residual nutrient support to wheat production, and 3) reducing nutrient losses to ground and surface waters. After 9 years, soil carbon (C) and soil N remained unchanged or declined slightly in the synthetic fertilizer treatment, but increased with use of compost amendments by 16-27% for C and by 13-16% for N. However, with hairy vetch cover crops, N leaching increased 4 times when compared to clover cover crops. September was the highest month for nitrate leaching, combining high rainfall with a lack of active cash crop or cover crop growth to use residual N. Broiler litter leaf compost (BLLC) showed the lowest nitrate leaching of all the nutrient amendments tested (P= 0.05).     

Enhancing Environmental Performance with Winter Cover Cropping after Potato Harvest in Eastern Canada

ABSTRACT

In humid climates, the risk of nitrate leaching and topsoil loss due to erosion is high on bare soil in the fall after potato (Solanum tuberosum L.) harvest and in the spring with snowmelt. This 2-year study (2016–2017) compared three winter cover crops. Two of these are used as cash crops (winter rye [Secale cereale L.], winter wheat [Triticum aestivum L.]), and one is a winter-killed cover crop (spring barley, Hordeum vulgare L.). They were all seeded on two dates after potato harvest (end of September or first week of October) in Prince Edward Island, Canada. The measured parameters included soil nitrate measured at different times in fall and in the following spring and summer, splash detachment, C and N contents in splashed sediments, cereal straw dry matter yield, and cereal grain yield. In both years, all winter cover crops decreased splash detachment compared with the no winter cover control, with winter rye having the greatest reduction. A similar trend was observed for C and N contents in splashed sediments. There was a trend toward lower soil nitrate following winter cover crops in comparison with bare soil, but the trend was not consistent across trials and sampling dates. Winter wheat grain yield ranged from 4.5 to 7.6 Mg ha^?1, while that associated with winter rye ranged from 3.2 to 5.1 Mg ha^?1. Therefore, winter cereal seeded after potato harvest can constitute a good source of revenue while mitigating the risk of soil erosion and reducing nitrate leaching in some cases.     

Nitrogen fertilization and cropping system impacts on soil properties and their relationship to crop yield in the central Corn Belt, USA

Evaluating the effects of management practices on soil physical and chemical properties would be valuable to explain field-level variability in crop production. A 23-year-old experiment on a Muscatune soil (fine-silty, mixed, superactive, mesic, Aquic Argiudolls) in Illinois with five N rates [0 (N₀), 70 (N₁), 140 (N₂), 210 (N₃) and 280 (N₄) kg N ha⁻¹] and two cropping systems [continuous corn (Zea mays L.) (CC), and corn–soybean (Glycine max (L.) Merr.) rotation (CS)] was evaluated. Specific objectives were to: (i) evaluate the effects of long-term N fertilization and cropping systems on field level changes in soil physical and chemical properties and crop yield, (ii) identify the most responsive soil physical and chemical properties to N fertilizer and crop management, and (iii) investigate the relationship between the selected soil properties and crop yield. Soil was collected in May 2004 to 30 cm depth and 20 soil physical and chemical properties were measured. The univariate analysis indicated that 14 soil properties were significantly influenced by at least one treatment effect (crops, N or crops × N). Due to multicollinearity among soil properties, principal component analysis (PCA) was used to group correlated properties, resulting in five soil properties such as soil organic carbon stock (OC stock), mean weight diameter (MWD), soil C:N ratio, exchangeable potassium (K⁺) and gravimetric moisture content (ω). Finally, the multiple regression analysis performed between PCA derived soil properties and corn and soybean yields retained all the representative soil properties from PCA except ω as yield predictors for corn (P < 0.001, R² = 0.39) from CC system, whereas none of the soil properties were significantly related to corn and soybean yields from CS system. The soil properties most influenced by long-term N fertilization of continuous corn were successfully identified with PCA and multiple regression. The insignificant relationship between corn and soybean yields from CS system and PCA derived soil properties might be due to the lack of response of soybean to N fertilization. This study shows the integrated use of multivariate and regression analyses in identifying yield determining soil properties by eliminating the multicollinearity among soil properties.     

Evaluation of four different crops’ sensitivity to sulfosulfuron and tribenuron methyl soil residues

ABSTRACT

On the basis of greenhouse bioassays, the sensitivities of root and shoot biomass of barley (Hordeum vulgare L.), corn (Zea mays L.), oilseed rape (Brassica napus L.) and sugar beet (Beta vulgaris L.) to soil-incorporated sulfosulfuron and tribenuron methyl were assessed. Shoot and root biomass production was measured 30 days after emergence. Plant responses, including roots and shoots dry weight per pot, were described by a three parameter log-logistic regression model as a function of sulfosulfuron or tribenuron methyl doses and the relative sensitivities were calculated at the various ED-levels with their associated 95% confidence intervals. The most precise ED-levels were that at ED₅₀ and sensitivity rank was oilseed rape, sugar beet, corn and barley, whatever the chosen response level and herbicide. We calculated relative sensitivities at ED₁₀, ED₅₀ and ED₉₀ for the species of barley, the most tolerant crop, as reference. Comparison of relative sensitivity of crops to both herbicides showed that the sensitivity of these crops was much larger for tribenuron methyl than for sulfosulfuron. Oilseed rape was the most sensitive species (ED₅₀?=?0.202 and 0.179?µg?kg^?1 soil for root dry weight (RDW) response to sulfosulfuron and tribenuron methyl, respectively) while barley was the most tolerant one (ED₅₀?=?1.008 and 3.68?µg?kg^?1soil for RDW response to sulfosulfuron and tribenuron methyl, respectively). Sugar beet and corn had intermediate sensitivity. Also, we demonstrated how important it is to show the confidence intervals of relative sensitivities. In several instances the relative sensitivities, even numerically large, were not significantly different from 1.00. We demonstrate that classifying biotypes as resistant to a herbicide requires the threshold of resistance/susceptible (R/S) of 4.00 only be accepted if confidence intervals do not cover 1.00.     

Nitrogen response of no‐till corn in first and second years following conservation reserve program

Abstract

A considerable amount of land enrolled in the Conservation Reserve Program (CRP) has been and will be returned to row crop production. It is difficult to predict how to manage nitrogen (N) fertilizer for these row crops, since there are plausible reasons to expect either substantial N immobilization or substantial N mineralization due to the effects of CRP enrollment. Our objective was to characterize corn (Zea mays L.) yield response to N following CRP in order to develop N management recommendations. Corn was planted either directly into killed CRP sod (CRP‐corn) or following soybean [Glycine max (L.) Merr.] that had been planted into killed CRP sod (CRP‐SB‐corn)‐ We applied a range of N rates and determined the economically optimum N rate from the yield response data. In both years of the study, the optimum N rate for CRP‐corn was much higher (181 and 230 lb N acre^‐1 in 1996 and 1997, respectively) than theoptimum N rate for CRP‐SB‐corn(108 and 113 lb Nacre^‐1 in 1996 and 1997, respectively). CRP‐corn with no N fertilizer appeared extremely N deficient for the first half of the season. We observed a large flush of inorganic soil N in late summer of the first year out of CRP, but this N was apparently too late for optimum corn production that season. We recommend soybean as the first choice row crop to plant immediately following CRP. If corn is to be planted immediately following CRP, we recommend higher‐than‐normal N rates to optimize production.