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Subsurface banding of P fertilizer is more effective than broadcast and incorporation for annual crops on P-deficient sites. Subsurface banding in established alfalfa (Medicago sativa L.) may damage plants. This study compared spring-applied, broadcast dry monoammonium phosphate (MAP) and fluid ammonium polyphosphate (APP), and APP applied in surface bands with 15-, 30-, or 60-cm spacing, at rates equivalent to 0.5x and lx the soil test recommendation for yield, tissue P concentration, and P uptake at six sites. There was no difference in soil test P measured after the first cutting between broadcast MAP or APP. Yield responses to P occurred at all sites and ranged from a low of 0.7 Mg [ha.sup.-1] (7%) averaged across P rate, to 2.6 Mg [ha.sup.-1] (46%) at the 0.5x rate and 5.4 Mg [ha.sup.-1] (95%) at the lx rate above the 0 kg P [ha.sup.-1] treatment. Yield was higher with MAP than with APP for five of 19 individual harvests, while total yield was 1.0 Mg [ha.sup.-1] higher with MAP than with APP at one site-year. Phosphorus source effects on P concentration and uptake were similar to those on dry matter yield. There was a linear decrease in yield with increasing band spacing for one site-year and a quadratic response for another. Responses to band spacing in tissue P concentration for nine harvests suggest that band spacing of 15 and 30 cm may enhance P availability relative to broadcast or 60-cm spacing. In only one site-year did we find a yield advantage of MAP over APE or of surface band over broadcast APP. Abbreviations: MAE monoammonium phosphate; APE ammonium polyphosphate.

Aluminum toxicity and soil acidity are major constraints in alfalfa (Medicago sativa subsp, saliva) production in the world. Despite intense research efforts, neither an effective screening procedure nor an Al-tolerant alfalfa germplasm is available. This dictates the need for identifying a new source of Al-tolerant genes in the closely related species M. truncatula (barrel medic). Our objectives were to compare three Al tolerance screening methods: (i) a seedling-based hydroponics method, (ii) a soil-based plant method, and (iii) an Al-stressed seedling-based lumogallion root staining method in 32 M. truncatula accessions. The soil system compared the genotypes for dry root and shoot weights in unlimed soil and for relative weights. The lumogallion root staining of Al-stressed seedlings compared the genotypes for fluorescence intensity of Al-bound lumogallion within the root tips. In the hydroponics system, the genotypes were compared for root elongation and relative growth. The three methods were different from each other, with altered rankings for genotypes across the methods. The soil assay demonstrated a higher capacity for discriminating Al response among genotypes with a higher reprodudbility. Most of the genotypes that were Al-tolerant in soil were also Al-tolerant using the hydroponics and root staining methods. The results suggested that a combination of soil-based and hydroponics screening might be essential to identify Al-tolerant genotypes possessing multiple Al tolerance mechanisms.

There is considerable uncertainty relative to the emissions of [N.sub.2]O from legume crops. A study was initiated to quantify [N.sub.2]O fluxes from soils cropped to alfalfa (Medicago sativa L.) and soybean (Glycine max L.), and to improve our understanding of soil and climatic factors controlling [N.sub.2]O emissions from these crops. Measurements were made on three soils cropped to alfalfa, soybean, or timothy (Phleumpratense L.), a perennial grass used as a control. In situ soil-surface [N.sub.2]O emissions ([F.sub.N2O]) were measured 47 times during the 2001 and 2002 growing seasons. Soil water, N[H.sub.4]-N, N[O.sub.3]-N, and [N.sub.2]O contents, and soil temperature were also determined to explain the variation in gas fluxes. Emissions of [N.sub.2]O were small under the grass where very low soil mineral N content probably limited denitrification and [N.sub.2]O production. Soil mineral N contents under legumes were lip to 10 times greater than under timothy. However, soil mineral N contents and [F.sub.N2O] were not closely related, thus suggesting that the soil mineral N pool alone was a poor indicator of the intensity of [N.sub.2]O production processes. Higher [F.sub.N2O] were measured under legume than under timothy in only 6 out of 10 field comparisons (site-years). Moreover, the emissions associated with alfalfa (0.67-1.45 kg N [ha.sup.-1]) and soybean (0.46-3.08 kg N [ha.sup.-1]) production were smaller than those predicted using the emission coefficient proposed for the national inventory of greenhouse gases (alfalfa = 1.60-5.21 kg N [ha.sup.-1] ; soybean = 2.76-4.97 kg N [ha.sup.-1]). We conclude that the use of the current emission coefficient may overestimate the [N.sub.2]O emissions associated with soybean and alfalfa production in eastern Canada.

Research has been conducted on Salmonella enterica and Escherichia coli O157:H7. Results indicate that the cells of these bacteria are attached to alfalfa sprout roots, but only S. enterica is attached to sprouts and to sprout seed coats in large cell aggregates and in large numbers respectively.

Alfalfa (Medicago sativa L.) cultivars with multifoliolate (MF) leaves are being promoted as a source of high quality forage, but information is lacking about the effect of environment on MF expression. We studied the influence of air temperature and photoperiod on the MF trait and its association with leaf and stem morphology. We grouped plants from four cultivars into four MF expression classes (very low, 60% MF leaves). These plants were grown in four growth chamber environments combining cool (20/11 [degrees] C day/night) and warm (29/17 [degrees] C) air temperatures with short (13 h) and long (16 h) photoperiods. Photoperiod had a greater influence than temperature on MF expression (MF%, number of MF leaves total leaf [number.sup.-1]). Under long, MF expression of plants in very low, low, and medium MF expression classes declined linearly with increased maturity. Under short-days, MF% of these classes declined until bud, but then increased until maturity. Multifoliolate expression of plants in the high expression class decreased in the cool-long day environment, but maintained or increased MF% in other environments. At harvest, MF%, leafiness, and leaflet number per MF leaf were greater for short vs. long photoperiods, but were not affected by air temperature. Multifoliolate expression was positively correlated (r = 0.43) with leafiness and number of leaflets per MF leaf (r = 0.96), but was not correlated with stem characteristics. Individual MF leaves had larger leaf area but similar specific leaf weight as trifoliolate leaves in all environments. In evaluation of MF expression, stage of maturity, and environmental conditions should be standardized.

The changes in soil aggregation and organic carbon (C) content over five years beneath corn and alfalfa were determined. Soil aggregation improved under alfalfa with an asymptotic regression while the organic C improvement showed a sigmoidal shape. Improvements in aggregation wre larger than that for organic C. Under fallow and corn cropping, little variation in organic C and aggregation were observed. For these two conditions, the mean weight diameter of water-stable aggregates was positively related to the soil water content at the time of sampling.

This alfalfa takes nitrogen from soil, not air. Alfalfa, the queen of forages, may soon hold court in a new realm of environmental cleanup. Scientists in the ARS Plant Science [...]

In the absence of irrigation, water from a water table below the root zone can sometimes sustain crop growth. This study was conducted to determine whether alfalfa grown without irrigation, but in the presence of a water table below the root zone, can give normal yields. Three irrigation treatments were applied: irrigating during the first two growth cycles, irrigating during the first three growth cycles, and no irrigation restrictions for the four growth cycles of the irrigation season. Water-table depths midway between parallel tile drains were evaluated. Yields from the midway position between drains were compared with yields nearer the drains. The influence of occurrence/nonoccurrence of irrigation on yield was also tested by regression analysis. Water tables tended to be deeper in the absence of irrigation but differences were small among the three treatments. Yield was dependent on the occurrence of irrigation but not on water-table depth. Most important, nonirrigation caused an 80% drop in yield.

Research using alfalfa seedlings indicates that plants may not be especially vulnerable to the DNA-damaging effects of increasing ultraviolet radiation due to diminishing stratospheric ozone. The action spectrum or wavelength-dependent sensitivity at which alfalfa DNA-injury occurs in the form of cyclobutyl pyrimidine dimer induction was found to be at the unexpectedly long wavelength of 365 nm rather than 280 to 313 nm as had been postulated in previous forecasts of how ozone depletion will affect plants.

The identical characteristics between the stable, low-molecular-weight (LMW) RNA fractions of several rhizobial isolates of Phaseolus vulgaris grown in the soil of Lanzarote, an island of the Canary Islands and a less-common pattern found within Sinorhizobium meliloti obtained from nodules of alfalfa and alfalfa-related legumes grown in northern Spain are presented. The bean isolates from Lanzarote not placed in the genus Rhizobium, showed inconsistancy with seed-borne transmission of Rhizobium etli from the Americas to the Canaries as an explanation for the presence of bean-nodulating rhizobia in soils of Lanzarote.

Research has been conducted on conjugative plasmid transfer from Pseudomonas putida to the indigenous bacterial community of alfalfa sprouts cultivated from the commercially available seeds. The authors have demonstrated that alfalfa spouts provide environment which allows efficient conjugant gene transfer between the colonizing bacteria, and that the tranconjugant formation occurs later.

Although alfalfa (Medicago sativa L.) stands have been reported to improve soil physical properties, little is known about the specific influences of above- and belowground alfalfa components on soil physical properties. A 2-yr study was conducted to investigate alfalfa root and shoot mulch modifications of soft physical properties and water movement in the root zone of a Kalamazoo loam soil (fine-loamy, mixed, mesic Typic Hapludalf) in southwest Michigan. Four treatments were considered: bare fallow (BF), bare fallow with alfalfa shoot mulch (BFSM), alfalfa with shoots removed and roots remaining (AR), and alfalfa with alfalfa shoot mulch (ASM). Volumetric soil water contents were measured by time domain reflectometry (TDR). Development of fine roots was monitored by minirhizotron technology. Alfalfa root systems increased saturated hydraulic conductivity ([K.sub.sat]) by 57%, total and macroporosities by 1.7 and 1.8%, respectively, and water recharge rate of the soil profile by as much as 5.4% per day. These effects of alfalfa roots on soil porosity were mainly attributed to increased amplitudes of wetting and drying cycles and high rates of root turnover in the Ap horizon. [K.sub.sat] was significantly correlated with macroporosity (r = 0.90, P [is less than or equal to] 0.01). Mean weight diameter (MWD) of aggregates from bare fallow soils was 20% higher when alfalfa shoot mulch was applied. Our results suggest that aggregate stability was more affected by C sources from shoot mulch and root turnover than by factors specific to root activities such as physical enmeshment of aggregates and increased soil wetting and drying cycles.