Alfalfa Management Research Articles

Effect of fall harvest time on forage yield and nutritive value of three alfalfa cultivars with different root types

AbstractWarmer than normal late fall temperatures may change standard fall harvest management of alfalfa (Medicago sativa L.) in western Canada. The objective of this study was to evaluate the forage yield and nutritive value of three types of alfalfa cultivars under different harvest managements. A field experiment was conducted from 2013 to 2017 using rhizomatous type (RR), cv. AC Yellowhead (M. sativa subsp. falcata), tap root type (TR), cv. Equinox (ssp. sativa) and creeping root type (CR), cv. Spredor 4 alfalfa (ssp. sativa), at Melfort, SK, Canada. The five harvest treatments were two 1‐cut systems (early July or late July) and three 2‐cut systems (early July + early or late September, late July + late September). Total forage yield was greater in TR and CR alfalfa than RR alfalfa; however, RR alfalfa had higher total forage yield under dry growing conditions versus CR alfalfa. The three alfalfa cultivars had a similar response to 2‐cut harvest managements. The first cut yield was affected by the timing of the second cut of the previous year with the early September harvest reducing yield more than the late September. Three alfalfa cultivars had similar crude protein (CP), total digestible nutrient (TDN), and acid detergent fiber (ADF) concentrations. There was a significant nutrient yield benefit of TR and CR alfalfa under a 2‐cut system over the RR alfalfa. Although the prairie climate is warming, the findings suggest that a fall rest period until late September is recommended regardless of alfalfa types to maintain high hay yield over multiple years.

Non-structural carbohydrates contributed to cold tolerance and regeneration of Medicago sativa L.

Soil water content only affected regeneration time, whereas the NSC content was related to the success of alfalfa regeneration. Non-structural carbohydrates (NSCs) are important factors influencing the overwintering and regeneration of alfalfa. In this study, we analyzed eight in-situ samplings at three depths of coarse roots (crown, 20 and 40cm depths) during the overwintering period and assessed the dynamic change and allocation of root NSCs under three irrigation frequencies (irrigation once every second day/4days/8days). Primary results showed that: (i) before cold acclimation, irrigation once every second day was beneficial to the accumulation of soluble sugars and starch in crown tissues, which would be maintained until the following spring and accelerate the regeneration time of alfalfa; (ii) during the overwintering process, the soluble sugars and starch contents in the crown were significantly higher than those in deeper roots, and there was an asynchronous effect caused by the change in soluble sugars and starch among roots at three depths; and (iii) the change trend of soluble sugar and starch contents was consistent with that of semi-lethal temperature, and there was a significant negativecorrelation between the content of soluble sugar (R2 = 0.8046) and starch (R2 = 0.6332) and the semi-lethal temperature. This study demonstrated that NSCs are the key driver of cold tolerance and regeneration under the three irrigation frequencies evaluated. Our results provide further insight into the allocation of NSCs in winter. This improved understanding of the mechanism of overwintering will allow for improved water management of alfalfa in high latitude areas.

Irrigation and Phosphorus Management of Alfalfa Under Semi-Arid Conditions

The frequency of irrigation and deficit irrigation management are drawing attention because water resources are becoming limited year by year, especially in the last decade. Besides, the rate and application time of P fertilization gained more importance just after the researchers found out it is more effective than N-fertilizing for alfalfa cultivation. This study aimed to determine the effects of different irrigation managements (seasonal deficit, intervals of 5, 7, and 9 days), phosphorus application season (autumn and spring), and the rate of P fertilizer (0, 30, 60, 90 kg ha-1) on the yield and forage quality of alfalfa. The experiment was conducted in the 2019-2020 years, which was the 3rd and the 4th years of alfalfa respectively, under semi-arid Mediterranean conditions. The stand height and fiber content (NDF) were higher in the autumn application. However, forage contained more nitrogen in the spring application. A higher amount of water (800 mm) with higher irrigation frequency (5 days – I5d) caused a reduction in yield due to water excess. The yield was the highest (21.34 t ha-1) and the forage quality was better in 448 mm water application with 9 days intervals (I9d). Seasonal deficit water management caused a significant loss in yield and quality. Nevertheless, 18.04 t ha-1 dry matter yield with 24.05 % CP content was recorded at seasonal deficit water management. P fertilization increased the yield and forage quality. The yield was the highest (20.23 t ha-1) at the rate of 90 kg ha-1 P fertilizer, but yield and forage quality characteristics were similar between 30, 60, and 90 kg ha-1 P. The results showed that P fertilization could be done in both autumn and spring at the rate of 30 kg ha-1 and 448 mm water could be applied at 9 days intervals for fulfilling performance under semi-arid Mediterranean conditions. When water resources are very scarce, the seasonal water deficit should be applied, especially in late summer.

Development of Online Alfalfa Management Extension Education Resources Amid the COVID-19 Pandemic

Prior to the COVID-19 pandemic, many Extension programs used web-based resources but balanced those with in-person events for interpersonal connection with producers and for individuals with limited access to technology. In 2020, in-person Extension programs were cancelled or converted to online versions. This was the case for the ‘Alfalfa in the South’ (AITS) program, a collaboration between Auburn University (AU) and University of Georgia (UGA). Two online AITS programs were held (May and Sept) and are examples of rethinking traditional models and optimizing resources to prioritize our commitment to clientele. In its first program, the program content was delivered through 1) a series of webinars from AU, UGA and University of Florida (UF) Extension Specialists (n = 6 webinars) and a 1-h live roundtable discussion held through Zoom on May 13, 2020. The roundtable consisted of a moderator interacting with five panelists (faculty, Extension agents and producers) answering live questions from the audience (n = 45 participants). All content was archived by the Alabama Cooperative Extension System (ACES) for later access using online resources. The second program occurred in Sept 2020 as a collaboration between AU, UF and UGA Specialists. This program included several pre-recorded short videos and e-publications on topics in establishment and management of alfalfa in the South. In 2020, the web-metrics gathered for the ACES webpage and Youtube channel across these programs sums over 3000 views of alfalfa resources. Similarly, engagement on the AL Beef and Forage Extension Facebook pages were over 3000 people. Although a traditional formal post-programming survey was not conducted with participants, an online survey was distributed simultaneously in the south region (n = 12 states) from May through December 2020 aiming to identify main challenges and limitations of alfalfa adoption. The results (n = 212 respondents) showed approximately 65% participants already invested time in learning about alfalfa using Extension online programs and resources available. This shows increased importance of online outreach as a tool to maintain relevance and connection with clientele.

Biomass Production and Nutrient Status of Alfalfa (Medicago Sativa L.) In Response to Boron Supply in Sandy Soil

ABSTRACT Boron (B) fertilization management of alfalfa, as perennial crop, requires to identify its sensitivity to B and its nutrients status after B supply for different forage harvests. The response of alfalfa to B supply, when grown on a Mediterranean sandy soil, was evaluated at different cuts. The native soil B content was around 0.15 mg kg−1, which was considered as B deficient. 19 cuts were evaluated in container experiment during three successive production seasons: 2016 (5 cuts), 2017 (7 cuts), and 2018 (7 cuts). Six soil B supplies were tested: 0 (control), 0.2, 0.5, 1, 5, and 10 mg kg−1. B was added in the sodium form. It was split equally between sowing and after the first cut for each rate. The results revealed that B deficiency symptoms did not induce a negative impact on total biomass production and protein content. Shoot B content of all cuts increased with increasing B rates. The lowest shoot B levels (<35 mg kg−1) were recorded in control after five successive cuts. B uptake for each cut can be predicted using the regression model: y (mg kg−1 of soil) = 0.018 x–0.01 z + 0.14 (adjusted R2 = 0.61) where x = soil B supply (mg kg−1) and z = cut number during growing seasons (from 1 to 19). The residual soil B was less than 0.5 mg kg−1, after 19 cuts, for different B rates. The results suggest that alfalfa seems not to be affected by B deficiency particularly during the first 3 years of production in sandy soil.

67 2018 Alfalfa in the South Workshop Series: A review of regional Extension efforts

Abstract Alfalfa research in the Southeast has steadily increased over the past ten years. Researchers have a renewed interest in this perennial legume as new varieties have been released that are better suited to the challenging climate and use in the Southeast. Extensive effort has been put forth in establishing programs promoting the use of alfalfa as a viable high-quality forage option in the south. In 2018, the “Alfalfa in the South” workshop series was designed to provide in-depth extension education, circulate new research findings, and engage in discussions with producers as related to the use of alfalfa in the southeast. The series consisted of 4 one-day workshops, organized by University of Georgia Extension in conjunction with America’s Alfalfa, and included Extension specialists, faculty, and graduate students from both the University of Georgia and Auburn University. Topics were broken into five classroom learning modules: 1) site selection and establishment, 2) improving animal performance with alfalfa, 3) managing alfalfa for persistence, 4) alfalfa breeding programs, and 5) graduate student research updates. Each workshop concluded with an on-farm demonstration where attendees engaged in discussion with producers utilizing alfalfa in their operation. Postworkshop evaluation results determined that, on a scale of 1 to 5, where “1” was “no change” and “5” indicated “greatly improved,” producers rated their change in interest using alfalfa as a 4.73 and their confidence in using alfalfa management skills as 4.36. Additionally, the producer discussion and field tour section rated the highest, 4.67 (1 being “poor” and 5 being “excellent”); however, all topics rated 4.12 or higher, indicating that attendees found this workshop to be very good to excellent. Of the 60 participants, 68% indicated that they would make some major changes and 32% plan to try to make minor management changes following the workshops.

Bayesian measurement error correction in structured additive distributional regression with an application to the analysis of sensor data on soil–plant variability

The flexibility of the Bayesian approach to account for covariates with measurement error is combined with semiparametric regression models for a class of continuous, discrete and mixed univariate response distributions with potentially all parameters depending on a structured additive predictor. Markov chain Monte Carlo enables a modular and numerically efficient implementation of Bayesian measurement error correction based on the imputation of unobserved error-free covariate values. We allow for very general measurement errors, including correlated replicates with heterogeneous variances. The proposal is first assessed by a simulation trial, then it is applied to the assessment of a soil-plant relationship crucial for implementing efficient agricultural management practices. Observations on multi-depth soil information forage ground-cover for a seven hectares Alfalfa stand in South Italy were obtained using sensors with very refined spatial resolution. Estimating a functional relation between ground-cover and soil with these data involves addressing issues linked to the spatial and temporal misalignment and the large data size. We propose a preliminary spatial interpolation on a lattice covering the field and subsequent analysis by a structured additive distributional regression model accounting for measurement error in the soil covariate. Results are interpreted and commented in connection to possible Alfalfa management strategies.

Cutting management and alfalfa stand age effects on organically grown corn grain yield and soil N availability

AbstractAlfalfa is recommended as a rotational crop in corn production, due to its ability to contribute to soil nitrogen (N) and carbon (C) stocks through atmospheric N2fixation and above- and belowground biomass production. However, there is little information on how alfalfa management practices affect contributions to soil and subsequent corn crop yields, and research has not been targeted to organic systems. A study was conducted to determine the effects of alfalfa stand age, cutting frequency and biomass removal on soil C and N status and corn yields at three organically managed Minnesota locations. In one experiment, five cutting treatments were applied in nine environments: two, three and four cuts with biomass removal; three cuts with biomass remaining in place; and a no-cut control. In the other experiment, corn was planted following 1-, 2-, 3- or 4-year-old alfalfa stands and a no-alfalfa control. Yield was measured in the subsequent corn crop. In the cutting experiment, the two- and three-cut treatments with biomass removal reduced soil mineral N by 12.6 and 11.5%, respectively, compared with the control. Potentially mineralizable N (PMN) was not generally affected by cutting treatments. The three-cut no-removal increased potentially mineralizable C by 17% compared with the other treatments, but lowered soil total C in two environments, suggesting a priming effect in which addition of alfalfa biomass stimulated microbial mineralization of native soil C. Although both yields and soil mineral N tended to be higher in treatments where biomass remained in place, this advantage was small and inconsistent, indicating that farmers need not forgo hay harvest to obtain the rotational benefits of an alfalfa stand. The lack of overall correlation between corn grain yields and mineral and potentially mineralizable N suggests that alfalfa N contribution was not the driver of the yield increase in the no-removal treatments. Alfalfa stand age had inconsistent effects on fall-incorporated N and soil N and C parameters. Beyond the first year, increased alfalfa stand age did not increase soil mineral N or PMN. However, corn yield increased following older stands. Yields were 29, 77 and 90% higher following first-, second- and third-year alfalfa stands than the no-alfalfa control, respectively. This indicates that alfalfa may benefit succeeding corn through mechanisms other than N contribution, potentially including P solubilization and weed suppression. These effects have been less studied than N credits, but are of high value in organic cropping systems.

Mass balance analyses of nutrients on California dairies to evaluate data quality for regulatory review

Effective regulations may help reduce nitrate contamination of groundwater from agriculture. Dairy farmers in California must maintain a ratio below 1.4 of total nitrogen (N) applied to total N-removed (N-Ratio) on cropland receiving manure application. In annual reports to the regulatory agency, farmers detail nutrients applied to cropland, removed in harvests, and exported off farm. Data were extracted from all available annual reports for 62 dairies from 2011, 2012, and 2013. Excretions of N, phosphorus (P), and potassium (K) were calculated using reported herd demographics and standard excretion equations from the American Society of Agricultural and Biological Engineers. Calculated nutrient excretion values were compared to the reported values of manure nutrients applied to cropland and exported off farm. Reported N-Ratios were compared to mass balance simulations exploring variable crop yields and alfalfa management. In the nutrient excretion balance, the distribution of the percent of N and P recovered in manures applied or exported peaked at 24% (median=31%) and 26% (median=53%) of excreted, respectively. The distribution of recovered K was fairly uniform from 0% to 300% (median=146%) of excreted K. In N-ratio simulations, 62% and 66% of all reported N-ratios were lower than their respective simulated N-ratio, assuming alfalfa crops received no N fertilization and minimal fertilization (26% of N-removed in harvest) respectively. When simulated crop yields were normally (sd=0.25) or Student's t distributed (df=154) around expected crop yields, 28% and 57% of all reported ratios fell within the 95% confidence interval of the simulations, respectively. Low and erratic recovery rates of excreted P and K existed. Additionally, reported N-Ratios were generally lower and more varied than necessary for farmers to maintain crop yields while complying with regulations. Greater understanding of low recovery rates is needed before data are used to assess the impact of regulations.

ALFALFA Nutrient and irrigation management

Once a good stand of alfalfa has been established, continued production and stand life depends on good management practices, which include maintaining soil nutrients, applying manure judiciously, and irrigating properly. The following article is a section from the revised (2015) Alfalfa Management Guide, which is available for purchase here: www.societystore.org. Earn 1 CEU in Nutrient Management by reading this article and completing the quiz at www.certifiedcropadviser.org/certifications/self‐study/771.

A Simple Method for Estimating Effective Cation Exchange Capacity, Cation Saturation Ratios, and Sulfur Across a Wide Range of Soils

Cation exchange capacity (CEC) and soil S supply potential are important soil characteristics. The BaCl2-MgSO4 compulsive exchange (CECCE) method is recommended for measuring effective CEC (ECEC) of both calcareous and acidic soils. However, to reduce costs, soil testing laboratories typically report CEC estimated from agronomic soil test data (summation method; CECsum), a method that overestimates the ECEC of calcareous soils. Recently, guidance for sulfur (S) management of alfalfa (Medicago sativa L.) was derived based on a single, 30-min, 0.01-M CaCl2 soil extraction with a 1:5 (wt:vol) soil-to-solution ratio. We tested the hypothesis that a single, 5-min, 0.01-M SrCl2 soil extraction with a 1:10 (wt:vol) soil-to-solution ratio can be used to accurately estimate both ECEC and available S across a variety of soil types. Fifty New York agricultural soils (soil pH from 5.1 to 8.4) were analyzed for CECCE and cations extracted with Morgan, Mehlich 3, 1 M NH4OAc, 1 M NH4Cl, and 0.01 M SrCl2 (single and double extractions). The CECsum based on Mehlich 3, Morgan, 1 M NH4OAc, and 1 M NH4Cl extraction solutions greatly overestimated ECEC as measured by CECCE, whereas the CECsum based on a single extraction with 0.01 M SrCl2 correlated well with CECCE across all soils (slope, 1.0451; R2 = 0.8538). Extractable S in the 5-min 0.01-M SrCl2 solution correlated well with results of the 30-min 0.01-M CaCl2 extraction (slope, 0.9685; R2 = 0.9976). We conclude that a single 5-min 0.01-M SrCl2 extraction with 1:10 soil-to-solution ratio is a simple, rapid, and inexpensive method of estimating ECEC and plant-available S.

Soil and Tissue Testing for Sulfur Management of Alfalfa in New York State

Alfalfa (Medicago sativa L.) is an important forage crop in New York. During the past decades, atmospheric S deposition has decreased, raising questions about fertilizer S needs of alfalfa and soil and tissue testing as tools for S management. On‐farm, replicated trials were conducted in eight locations in New York comparing two S sources (CaSO4 and K2SO4×2MgSO4 at 168 kg S ha−1) applied after the first cutting in 2008 vs. a no‐S control. Four of eight sites were S responsive, averaging a 17% yield increase with S fertilization. Sulfur fertilization did not impact estimated milk production per unit yield for any of the cuttings or locations despite small S‐fertilization‐induced changes in protein levels at some locations. The greatest yield and response to S were measured for Site 5 (10.0 and 8.5 Mg ha−1 with and without S fertilization, respectively). The data suggest critical values of 2.7 g S kg−1 (tissue test) and 8 mg SO4–S kg−1 (0.01 mol L−1 CaCl2 extractable soil test) at which a 95% relative yield was obtained. Monitoring of soil S concentrations during a 5‐yr corn (Zea mays L.) and 4‐yr alfalfa rotation showed that recently manured fields are not likely to be S deficient, but soil S concentrations declined during the unmanured alfalfa years and soils could become S deficient. We concluded that both tissue and soil S tests have potential as indicators of S responsiveness for alfalfa. Additional research is needed to validate the suggested soil and plant tissue critical values.

Chemical properties and biological activity in soils of Mallorca following twenty years of treated wastewater irrigation

On the Mediterranean island of Mallorca, the use of secondary-treated municipal wastewater in irrigation was introduced with the construction of the first wastewater treatment plants in the 1970s. In this study, the chemical properties and biological activity of 21 arable soils, irrigated for more than 20 years with secondary-treated wastewater, were tested in order to assess their quality. Soil quality was evaluated by measuring cation exchange capacity, pH, calcium carbonate equivalent, soil organic matter, total nitrogen, available phosphorus, water-soluble organic carbon, soil microbial biomass, soil basal respiration, and the activities of the enzymes dehydrogenase, β-glucosidase and alkaline phosphatase. No negative effects of the irrigation treatment were observed on the measured soil parameters. Indeed, soil water-soluble organic carbon, soil microbial biomass and β-glucosidase and alkaline phosphatase activities increased under treated wastewater irrigation. Biological activity of soils irrigated with treated wastewater was affected mainly by soil organic matter content. Although the typical crop management of alfalfa, and other forage crops associated with treated wastewater irrigation, may have contributed to the increase of these parameters, the results suggest that irrigation with treated wastewater is a strategy with many benefits to agricultural land management.

Alfalfa management affects infestations of Lygus rugulipennis (Heteroptera: Miridae) on strawberries in northwestern Italy

Lygus rugulipennis (Heteroptera: Miridae) is a highly polyphagous plant bug that causes severe damage on everbearing strawberries in NW Italy. In this area strawberry fields are frequently surrounded by alfalfa and other forage crops on which plant bugs usually live and reproduce until mowing or harvest. A 3-year research study was conducted to test the attractiveness of some herbs, including alfalfa, for ovipositing L. rugulipennis females, and to evaluate if appropriate management of neighbouring forage crops could affect bug infestation levels and damage to strawberries. In 2005, the attractiveness to ovipositing females of four plant species (strawberry, alfalfa, red clover and chamomile), each of which is abundant in NW Italy, was evaluated in laboratory trials. In 2006 and 2007, the seasonal abundance of plant bugs on strawberries and alfalfa was monitored in an experimental strawberry field with a strip of alfalfa along two sides. During field surveys, the influence of alfalfa management, including insecticide treatments in 2007, on plant bug numbers was assessed. In the laboratory, females of L. rugulipennis preferred, in decreasing order, chamomile, alfalfa, red clover and strawberry for oviposition. However, in the field, the majority of nymphs were collected on strawberries over most of the growing season, showing that L. rugulipennis is able to reproduce and develop on this plant. During field surveys, more species of plant bugs, and more individuals, were observed on alfalfa, which although attractive for mirid bugs did not prevent their migration to strawberries during periods of high population density. At such times, an insecticide treatment on alfalfa kept plant bug infestations on strawberries under the economic threshold.

Pre‐crop effects of alfalfa management systems on inorganic soil nitrogen and cereals in organic farming under pannonian site conditions

Journal of Plant Nutrition and Soil ScienceVolume 171, Issue 4 p. 576-579 Short Communication Pre-crop effects of alfalfa management systems on inorganic soil nitrogen and cereals in organic farming under pannonian site conditions Renate de Kruijff, Renate de Kruijff Division of Organic Farming, Department of Sustainable Agricultural Systems, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, AustriaSearch for more papers by this authorGabriele Pietsch, Gabriele Pietsch Division of Organic Farming, Department of Sustainable Agricultural Systems, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, AustriaSearch for more papers by this authorBernhard Freyer, Bernhard Freyer Division of Organic Farming, Department of Sustainable Agricultural Systems, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, AustriaSearch for more papers by this authorJürgen K. Friedel, Jürgen K. Friedel [email protected] Division of Organic Farming, Department of Sustainable Agricultural Systems, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, AustriaSearch for more papers by this author Renate de Kruijff, Renate de Kruijff Division of Organic Farming, Department of Sustainable Agricultural Systems, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, AustriaSearch for more papers by this authorGabriele Pietsch, Gabriele Pietsch Division of Organic Farming, Department of Sustainable Agricultural Systems, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, AustriaSearch for more papers by this authorBernhard Freyer, Bernhard Freyer Division of Organic Farming, Department of Sustainable Agricultural Systems, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, AustriaSearch for more papers by this authorJürgen K. Friedel, Jürgen K. Friedel [email protected] Division of Organic Farming, Department of Sustainable Agricultural Systems, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, AustriaSearch for more papers by this author First published: 06 August 2008 https://doi.org/10.1002/jpln.200700257Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume171, Issue4August, 2008Pages 576-579 RelatedInformation

The ecology and economics of insect pest management in nut tree alley cropping systems in the Midwestern United States

The potential ecological benefits of an alternative agronomic practice such as alley cropping are numerous, but the practice is unlikely to be adopted unless it is economically viable. We investigated insect pest dynamics, crop yields, and small farm economics in an alley cropping practice of alfalfa and black walnut compared to conventionally grown alfalfa. We examined the mortality factors affecting alfalfa weevil, Hypera postica (Gyllenhal), under normal monocultural alfalfa management and under an agroforestry practice of intercropping alfalfa with black walnut trees at two alley widths, 12.2 and 24.4 m. Alfalfa yields were determined for three harvest cycles over 2 years in the same system. Black walnut and alfalfa financial models were used to determine the economic viability of alfalfa-black walnut alley cropping based on yield results. We found that alfalfa weevil mortality was significantly higher for two of the four sampling dates in alley cropped alfalfa compared to monocropped alfalfa. Alfalfa yield from wider alleyways was not significantly different from monocropped alfalfa for the first harvest date, but lower thereafter, while yield from narrower alleyways was significantly lower than both wider alleyways and monocropped alfalfa. Financial models indicated alley cropping alfalfa at wider alley widths provided positive cash flow. Our results suggest alley cropping alfalfa with black walnut provides both ecological and economic benefits.

Alfalfa Management in No-tillage Corn

Glyphosate-resistant corn was no-till planted into alfalfa that was in the early bud stage (UNCUT) or had been cut 3 to 4 d earlier and baled for hay (CUT). Alfalfa control and corn yield were measured in nontreated plots as well as plots treated with glyphosate alone or tank-mixed with 2,4-D or dicamba applied at planting (AP) or POST. Alfalfa control was greater for all AP treatments of UNCUT compared to CUT alfalfa. Glyphosate plus dicamba applied AP controlled alfalfa better than the other AP treatments resulting in increased corn yield compared with other AP treatments. Postemergence applications of glyphosate alone or tank-mixed with 2,4-D or dicamba controlled alfalfa better 6 weeks after treatment than AP applications of the same herbicides; however, corn yield for AP treatments were similar or greater than the yield of POST applications of the same herbicides. Corn yield averaged 13% higher following herbicide applications to UNCUT compared with CUT alfalfa, so the value of alfalfa hay must be weighed against the loss of corn yield when making decisions concerning the management of an alfalfa–corn rotation.

Contribution of initial C and N reserves in Medicago sativa recovering from defoliation: impact of cutting height and residual leaf area.

We studied the effects of stubble carbon / nitrogen (C / N) reserves or residual leaf area (RLA) on the contribution of taproot C / N reserves to shoot regrowth of Medicago sativa L. after cutting. The study assessed the effects of two cutting heights (6 and 15 cm), two RLAs (0 or 100%), and two initial C / N reserve levels (high N or low N) on forage production, nitrogen (N) distribution, and C / N reserve dynamics within stubble and taproot.

Sod‐Seeding and Grazing Effects on Alfalfa Weevils, Weeds, and Forage Yields in Established Alfalfa

Alfalfa (Medicago sativa L.) hay production for dairy and equine industries is a profitable enterprise in the Great Plains. However, as stands thin, forage production decreases and weeds increase, resulting in decreased returns. The objective of this research was to determine if alternative management strategies using October sod seeding plus March grazing could be utilized to increase forage production and control pests. Experiments were conducted at four locations in central Oklahoma from 1998–2000. Two ungrazed treatments (with and without pesticides) were compared with three treatments without pesticides but grazed by cattle in March. The three grazing treatments included: no sod seed, ryegrass (Lolium multiflorum Lam.) sod‐seeded in October, and wheat (Triticum aestivum L.) sod‐seeded in October. Grazing by cattle reduced alfalfa weevil (Hypera postica Gyllenhal) larval populations as effectively as insecticide application. In thin stands (&lt;200 stems m−2), total forage yields were increased with alfalfa–grass mixtures by an average of 2.7 kg ha−1. However, alfalfa yields were decreased 0.9 kg ha−1 with sod‐seeded ryegrass (P = 0.05). In thin stands, sod‐seeded grass treatments were more effective at weed suppression than a herbicide treatment. Net returns from cool‐season forage production increased with sod seeding plus March grazing compared with net returns using conventional haying methods. In thin stands (&lt;200 stems m−2), sod seeding of ryegrass or wheat plus March grazing provided greater net returns ($175 ha−1) than conventional practice of using pesticides and haying. In full stands (&gt;250 stems m−2), net returns from conventional alfalfa management (using pesticides and only haying) were comparable to October sod seed plus March grazing treatments.

THE EFFECTS OF COMPOST AND CROP ROTATIONS ON CARBON TURNOVER AND THE PARTICULATE ORGANIC MATTER FRACTION

Management practices that influence the quantity of C inputs returned to the soil from cropping systems and compost applications alter subsequent biotic activity broadly, contribute to seasonal fluctuations in nutrient dynamics, and may increase C sequestration. The effects of crop rotations and compost applications on soil-C sequestration and decompostion, and the turnover time of C 4 -derived corn C were assessed via changes in the C content and 13 C values of particulate organic matter (POM) and total soil organic C (SOC). The majority of organic inputs entered the POM fraction, defined as the sand-sized soil separates remaining on a 53-μm sieve after removal of residues (>2 mm), dispersion in 5% sodium polyphosphate, and 12 h of shaking. Before the application of compost to soil, 85% of the C in the compost material was classified as POM. Measurements of POM-C in the soil were 45% higher and SOC was 16% greater where compost was applied in place of N fertilizer. Addition of compost to POM-C diminished the value of POM as an indicator of short-term changes in nutrient dynamics. However, POM-C remaining from compost applications made during the period 1993 to 1997 may be an indicator of enhanced macroaggregate stability: improved soil tilth and the retention of soil C and N. The turnover time of C 4 -derived C in the POM fraction was 11 years compared with 22 years in SOC. The presence of compost C did not affect the turnover time of corn-derived C. High cropping intensity and chisel plow management increased C sequestration relative to the preceding alfalfa management.