Cover crop potential of winter oilseed crops in the Northern U.S. Corn Belt

ABSTRACT

Winter camelina [WC, Camelina sativa (L.) Crantz] and field pennycress (FP, Thlaspi arvense L.) are emerging oilseed crops in corn–soybean rotations, but little is known about their cover crop potential. A 2-year study was conducted in Minnesota, USA to evaluate the effect of winter oilseed crops on nitrogen (N) use, growth and yield of corn and soybean. Treatments included WC, FP, winter rye (WR, Secale cereale L.), and a no cover crop (NC) control. Oilseed crops produced 40–50% less spring biomass and accumulated less N compared to WR. The tissue-N of WC and FP was 39.0% and 6.6% higher than WR, respectively. The C:N ratio of cover crops was lower than 20:1, suggesting rapid decomposition. Compared with NC, cover crops lowered soil nitrate before major crops planting, but the post-harvest N profile following corn and soybean was not affected. Compared with NC, cover crops significantly decreased corn yield, with 8.7%, 9.5% and 9.8% reduction following WC, FP and WR, respectively. Cover crops did not affect growth, yield and N uptake of soybean. Oilseed crops showed potential to improve N cycling in the rotation, but more research of their impact on major crops is needed.     

Response of Different Crops to Arbuscular Mycorrhiza Fungal Inoculation in Phosphorus-Deficient Soil

Arbuscular mycorrhizal fungi (AMF) have the capability to improve crop yields by increasing plant nutrient supply. A pot experiment was conducted under natural conditions to determine the response of AMF inoculation on the growth of maize (Zea mays L.), sorghum (Sorghum bicolor L.), millet (Pennisetum glaucum L.), mash bean (Vigna mungo L.), and mung bean (Vigna radiata. L.) crops during 2008. The experiment was conducted as a completely randomized design in three replications using phosphorus (P)–deficient soil. Three plants were grown in 10 kg soil up to the stage of maximum growth for 70 days. Spores of AMF were isolated from rhizosphere of freshly growing wheat and berseem crops and mixed with sterilized soil with fine particles. Crops were inoculated in the presence of indigenous mycorrhiza with the inoculum containing 20 g sterilized soil mixed with 40–50 AMF spores. Inoculation with AMF improved yield and nutrient uptake by different crops significantly over uninoculated crops. Inoculated millet crop showed 20% increase in shoot dry matter and 21% in root dry matter when compared with other inoculated crops. Increases of 67% in plant nitrogen (N) and iron (Fe) were observed in millet, 166% in plant P uptake was observed in mash beans, 186% in zinc (Zn) was measured in maize, and 208% in copper (Cu) and 48% in manganese (Mn) were noted in sorghum crops. Maximum root infection intensity of 35% by AMF and their soil spore density were observed in millet crop followed by 32% in mash beans. Results suggest that inoculation of AMF may play a role in improving crop production and the varied response of different crops to fungi signifies the importance of evaluating the compatibility of the fungi and plant host species.     

Impact of a 5-year winter cover crop rotational system on the molecular diversity of arbuscular mycorrhizal fungi colonizing roots of subsequent soybean

The impact of winter cover crops, specifically wheat (Triticum aestivum L.), red clover (Trifolium pratense L.), and rapeseed (Brassica napus L.) or winter fallow, on community composition of arbuscular mycorrhizal fungi (AMF) in subsequent soybean roots was investigated in a 5-year field trial on andosolic soils in Japan. Soybean roots were sampled at full-flowering and analyzed for AMF communities using a partial LSU rDNA region. Phylogenetic analysis detected 22 AMF phylotypes, including eight Glomus, three Gigaspora, two Scutellospora, three Acaulospora, two Rhizophagus, and one of Funneliformis, Diversispora, Paraglomus, and an unknown glomeromycete in the roots. The 5-year rotation of different winter cover crops or winter fallow did not impact the molecular diversity of AMF communities colonizing the roots of subsequent soybean. In all of the rotations, Glomus and Gigaspora phylotypes were common to soybean roots over the 5-year period. Redundancy analysis (RDA) demonstrated that AMF communities in the roots of subsequent soybean were not significantly different among winter cover crop rotations or fallow. However, AMF communities in soybean roots were clearly influenced by rotation year suggesting that climate or other environmental factors were more important than winter cover cropping system management.     

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.     

Corn Residue Removal Effects on Hydraulically Effective Macropores

Enhanced understanding of biomass removal effects on soil quality could be achieved with greater knowledge of how corn residue removal and cover crops interact to affect surface pore structure. This study was conducted to evaluate the effects of corn (Zea mays L.) residue removal on soil macropore characteristics and to assess the effectiveness of cover crops in mitigating the potential negative impacts of corn biomass removal on surface pore structure. Three different corn residue removal rates and the presence or absence of cover crops were evaluated in a no-till corn/soybean (Glycine max L.) rotation near Brookings, SD. Following eight years of residue removal high (HRR) and medium (MRR) rates of residue removal reduced water inflow into the soil surface compared to the low (LRR) residue removal treatment. The representative mean pore radius (λ_Δψ) for both rotation phases of LRR approached the same value (≈ 235 µm). However, nine months after corn residue removal the λ_Δψ for HRR in the soybean phase of the rotation was significantly lower than LRR at 161 µm. There was no significant difference in λ_Δψ between HRR (214 µm) and LRR (236 µm) 21 months after residue removal during the corn phase of the rotation. The initial reduction in λ_Δψ following corn residue removal in HRR followed by soil surface recovery the following year suggests that inclusion of decaying corn residue is critical in the maintenance of hydraulically functional macropores in this fine textured soil. Cover crops were not observed to mitigate these impacts of crop residue removal on surface soil structure within the time period of the study.     

Crop Productivity and Nutrient Bioavailability in a Potato-Based Three-Year Rotation as Affected by Composted Pulp Fiber Residue Application and Supplemental Irrigation

The possibility of using composted pulp fiber residues (CPFR) in a potato rotation in eastern Canada was tested. Three rates of CPFR (0, 45, and 90 Mg C ha^?1) with or without supplementary irrigation were applied. Pea (Pisum sativum L.), corn (Zea mays L.), and potato (Solanum tuberosum L.) were cultivated in 2002, 2003, and 2004, respectively. Soil total carbon (C) and nitrogen (N), bulk density, and water-holding capacity were improved by CPFR. Pea and corn yields and total dry matter were increased using CPFR. Supplemental irrigation increased pea yield compared with the rain-fed system. Total tuber yield was increased by CPFR in the irrigated but not in the rain-fed system. The CPFR application increased plant-available phosphorus (P) and potassium (K) in all rotation crops. Nitrogen accumulation in all rotation crops except potato was increased by CPFR. The CPFR application successfully enhanced soil fertility and crop productivity without any adverse effects.     

Effect of indigenous mycorrhizal colonization on phosphorus‐acquisition efficiency in soybean and sunflower

Despite a general consent about the beneficial contribution of arbuscular mycorrhizal fungi (AMF) on natural ecosystems, there is an intense debate about their role in agricultural systems. In this work, soybean (Glycine max L.) and sunflower (Helianthus annuus L.) field plots with different P availabilities were sampled across the Pampean Region of Argentina (> 150 samples from Mollisols) to characterize the relationship between available soil P and indigenous mycorrhizal colonization. A subsequent pot experiment with soybean and sunflower was carried out to evaluate the effect of P supply (0, 12, and 52 mg P kg^–1) and AMF inoculation on AMF colonization and crop responsiveness to P in a Mollisol. Both crops showed high AMF colonization in the field (average: 55% for soybean and 44% for sunflower). While mycorrhizal colonization in soybean was significantly and negatively related to available soil P, no such trends were apparent in sunflower. Also, total biomass was 3.5 and 2.0 times higher in mycorrhizal than in nonmycorrhizal pot‐grown soybean under low‐ and medium‐P conditions, respectively. Sunflower, on the other hand, did not benefit from AMF symbiosis under medium and high P supply. While mycorrhization stimulated P‐uptake efficiency in soybean, the generally high P efficiency in sunflower was not associated with AMF symbiosis.     

Soil microbial properties in Bt (Bacillus thuringiensis) corn cropping systems

Growing Bt crops reduces the use of insecticides applied to them, but these crops could affect soil microorganisms and their activities. We evaluated the effects of Bt (Cry1Ab) corn (Zea mays L.) and deltamethrin ([S]-α-cyno-3-phenoxybenzyl [1R, 3R]-3-[2,2-dibromovinyl]-2,2-dimethylcyclopropane-1-carboxylate) insecticide application on soil microbial biomass C (MBC), β-glucosidase enzyme activity (final season only), bacterial functional diversity, and bacterial community-level physiological profiles (CLPPs) in corn monoculture in five seasons. We also determined if growing Bt corn in crop rotation would alter these effects. Statistical analysis of pooled data across seasons did not show any effects of Bt technology, insecticide application or crop rotation on soil microbial biomass or diversity even though differences between seasons and between the rhizosphere and bulk soil were observed. Annual analyses of results also showed that neither the Bt technology nor insecticide application affected soil MBC, enzyme activity, or functional diversity of bacteria in corn rhizosphere, but shifts in bacterial CLPPs due to Bt trait were observed in one year. Crop rotation effects on soil microbial properties were not observed in most cases. Where effects were observed, Bt corn grown in rotation resulted in greater MBC, enzyme activity and functional diversity than Bt corn grown in monoculture or conventional corn grown in rotation, and these effects were observed only in bulk soil. Therefore, the Bt technology is safe with respect to the non-target effects measured in this study. However, the effects of repeated use of Bt crops over many years on the soil environment should continue to be monitored.     

Long‐term effects of lime and gypsum additions on no‐till corn and soybean yield and soil chemical properties in southern Brazil

A long‐term experiment on a clayey, kaolinitic, thermic Rhodic Hapludox where dolomitic lime was applied to the surface (either at 4.5 t/ha or at 1.5 t/ha per yr for 3 yr), or incorporated into the topsoil (4.5 t/ha), and gypsum applied to the surface (3, 6, and 9 t/ha), was carried out to evaluate their effects on soil profile chemical properties and yields of corn (Zea mays L.) and soybean (Glycine max L. Merrill). Lime applied to the soil surface at either full or split rates, or incorporated and surface‐applied gypsum had long‐lasting effects on soil acidity or calcium and sulphur availability respectively, as measured 8 yr after application. Grain yields of corn and soybean were not influenced by liming. Gypsum at 9 t/ha significantly increased corn grain yields by 7 and 8% respectively 7–10 yr after application, but did not affect soybean grain yields. The differences in response of the corn and soybean crops to gypsum might be related to the Ca²⁺ uptake by plants because of cation exchange properties of roots, being smaller for corn than for soybean. The use of gypsum in no‐till systems becomes more viable when corn is grown with a greater frequency in crop rotation.     

Effect of agricultural management practices on arbuscular mycorrhizal fungal abundance in low-input cropping systems of southern Africa: a case study from Zimbabwe

Previous research, mostly in temperate agricultural systems, has shown that management practices such as fallow period, tillage, crop rotation, and phosphorus (P) fertilizer applications can influence the abundance of arbuscular mycorrhizal fungi (AMF), but relatively little is known about their effect in smallholder farmers’ fields in sub-Saharan Africa. In this study, we evaluated the effect of four subsistence crops that form associations with AMF, moderate P fertilization, tillage, and fallow period on the subsequent AMF abundance on three contrasting low fertility soils in south-western Zimbabwe. Arbuscular mycorrhizal fungal abundance was estimated based on early mycorrhizal colonization of maize (Zea mays L.) or lablab (Lablab purpureus L.) following the various treatments. The previously grown crop significantly affected AMF abundance (p < 0.001). It was highest after lablab followed by pigeonpea (Cajanus cajan L.), maize, and groundnut (Arachis hypogaea L.), and there were significant positive correlations between AMF abundance and aboveground biomass of pigeonpea, lablab, and maize. Contrary to much previous research, P fertilization, fallowing, and tillage did not significantly decrease AMF abundance. In smallholder farmers’ fields in the semi-arid tropics of sub-Saharan Africa, therefore, growing vigorous mycorrhizal plants prior to the dry season could be more important than minimizing P fertilizer applications, fallow periods, and tillage to maintain or increase AMF abundance.     

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.     

Aggregate stability and glomalin in alternative crop rotations for the central Great Plains

 Land productivity, along with improvement or maintenance of soil health, must be evaluated together to achieve sustainable agricultural practices. Winter wheat-fallow (W-F) has been the prevalent cropping system in the central Great Plains for 60 years where moisture is a limitation to crop production. Alternative cropping systems show that producers can crop more frequently if residue management and minimum tillage are used. The impact of different crops, crop rotations and tillage management practices on soil quality was assessed by measuring aggregate stability and glomalin production by arbuscular mycorrhizal (AM) fungi in soil from cropping trials established in 1990. Crops were wheat (W), corn (C), proso millet (M), and sunflower (S). Rotations sampled were W-F, W-C-M, W-C-M-F, W-C-F, and W-S-F. In the same area as the cropping trials, soils were taken from a perennial grass (crested wheatgrass) and from a buffer area that had been planted to Triticale for the past 2 years but prior to that had been extensively plowed for weed control. We found that aggregate stability and glomalin were linearly correlated (r=0.73, n=54, P<0.001) across all treatments sampled. Highest and lowest aggregate stability and glomalin values were seen in perennial grass and Triticale soils, respectively. Aggregate stability in W-S-F was significantly lower than in the other crop rotations (P≤0.03), while W-C-M had significantly higher glomalin than the other rotations (P<0.05). Differences between crop rotations and the perennial grass indicate that selected comparisons should be studied in greater detail to determine ways to manage AM fungi to increase glomalin and aggregate stability in these soils. Received: 16 March 1999     

Doybean growth and composition as affected by K,Ca, and Mg rates and corn rotation

Abstract

Different rates of K, Ca, and Mg were applied to bulklots of Decatur clay loam (pH 5.8) which had been collected from an area under natural vegetation. Nitrogen and P were each applied at the rate of 100 ppm. Soybean (Glycine max L.) and corn (Zea mays L.) were planted to pots in four replications of each treatment. Plants were grown for 6 weeks and subsequently all the pots were re‐planted to soybeans. This crop rotation was repeated until six crops had been harvested from each pot.

Potassium fertilization did not affect soybean growth but increased the dry matter of corn plants. Calcium application affected the growth of neither crop, but Mg addition to the soil reduced the growth of both crops. The composition of the plants generally reflected the available amounts of each nutrient. Additionally, Mg consistently decreased K in soybeans but increased Mn in the two crops. The inclusion of corn in rotation with soybeans resulted in the following effects on the succeeding soybean harvests: more tolerance to high Mg, greater reduction of plant Ca and Mg caused by K application, and lower levels of available K and Ma in soils and soybeans. However, the greater rate of depletion of soil K and Mn under corn rotation did not appear Co affect the dry matter yields of the following soybean plants relative to the plants under the continuous soybean cropping system.     

Contrasting grain crop and grassland management effects on soil quality properties for a north-central Missouri claypan soil landscape

Abstract

Crop management has the potential to either enhance or degrade soil quality, which in turn impacts on crop production and the environment. Few studies have investigated how crop management affects soil quality over different landscape positions. The objective of the present study was to investigate how 12 years of annual cropping system (ACS) and conservation reserve program (CRP) practices impacted soil quality indicators at summit, backslope and footslope landscape positions of a claypan soil in north-central Missouri. Claypan soils are particularly poorly drained because of a restrictive high-clay subsoil layer and are vulnerable to high water erosion. Three replicates of four management systems were established in 1991 in a randomized complete block design, with landscape position as a split-block treatment. The management systems were investigated: (1) annual cropping system 1 (ACS1) was a mulch tillage (typically ≥ 30% of soil covered with residue after tillage operations) corn (Zea mays L.)–soybean (Glycine max (L.) Merr.) rotation system, (2) annual cropping system 2 (ACS2) was a no-till corn–soybean rotation system, (3) annual cropping system 3 (ACS3) was a no-till corn–soybean–wheat (Triticum aestivum L.) rotation system, with a cover crop following wheat, (4) CRP was a continuous cool-season grass and legume system. In 2002, soil cores (at depths of 0–7.5, 7.5–15 and 15–30 cm) were collected by landscape position and analyzed for physical, chemical and biological soil quality properties. No interactions were observed between landscape and crop management. Relative to management effects, soil organic carbon (SOC) significantly increased with 12 years of CRP management, but not with the other management systems. At the 0–7.5-cm soil depth in the CRP system, SOC increased over this period by 33% and soil total nitrogen storage increased by 34%. Soil aggregate stability was approximately 40% higher in the no-till management systems (ACS2 and ACS3) than in the tilled system (ACS1). Soil aggregation under CRP management was more than double that of the three grain-cropping systems. Soil bulk density at the shallow sampling depth was greater in ACS3 than in ACS1 and ACS2. In contrast to studies on other soil types, these results indicate only minor changes to claypan soil quality after 12 years of no-till management. The landscape had minor effects on the soil properties. Of note, SOC was significantly lower in the 7.5–15-cm soil depth at the footslope compared with the other landscape positions. We attribute this to wetter and more humid conditions at this position and extended periods of high microbial activity and SOC mineralization. We conclude that claypan soils degraded by historical cropping practices will benefit most from the adoption of CRP or CRP-like management.     

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.     

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.     

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.     

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.     

Effect of cropping systems on nitrogen mineralization in soils

 Understanding the effect of cropping systems on N mineralization in soils is crucial for a better assessment of N fertilizer requirements of crops in order to minimize nitrate contamination of surface and groundwater resources. The effects of crop rotations and N fertilization on N mineralization were studied in soils from two long-term field experiments at the Northeast Research Center and the Clarion-Webster Research Center in Iowa that were initiated in 1979 and 1954, respectively. Surface soil samples were taken in 1996 from plots of corn (Zea mays L.), soybean (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) that had received 0 or 180 kg N ha^–1 before corn and an annual application of 20 kg P and 56 kg K ha^–1. N mineralization was studied in leaching columns under aerobic conditions at 30  °C for 24 weeks. The results showed that N mineralization was affected by cover crop at the time of sampling. Continuous soybean decreased, whereas inclusion of meadow increased, the amount of cumulative N mineralized. The mineralizable N pool (N _o) varied considerably among the soil samples studied, ranging from 137 mg N kg^–1 soil under continuous soybean to >500 mg N kg^–1 soil under meadow-based rotations, sampled in meadow. The results suggest that the N _o and/or organic N in soils under meadow-based cropping systems contained a higher proportion of active N fractions. Received: 10 February 1999     

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.