Reduced Fertilizer Inputs Research Articles

Integration of cover crops and fertilizer rates for weed management in celery

Field studies were carried out in Laingsburg, MI, from 2002 to 2004 on Houghton muck soil to assess the impacts of cover crops and soil fertility regimes on weed populations and celery yield. The cover crops were oilseed radish, cereal rye, hairy vetch, and a bare ground control. The fertility rates were full (180, 90, and 450 kg ha−1nitrogen [N], phosphorus pentoxide [P2O5], and potassium oxide [K2O], respectively), half (90, 45, and 225 kg ha−1N, P2O5, and K2O, respectively), and low (90 kg ha−1N). Each cover crop treatment was combined with the low or half rate of fertilizer. An additional treatment with bare ground plus the full rate of fertilizer was added as standard practice. Treatments were maintained in the same location for the duration of the study. Major weed species were common chickweed, prostrate pigweed, shepherd's-purse, common purslane, and yellow nutsedge. Each year, oilseed radish consistently produced the greatest biomass and provided over 98% early season weed biomass suppression. Hairy vetch and cereal rye provided about 70% weed suppression in early spring. Soil fertility level affected weed populations during the 2004 growing season. In 2004, weed biomass in treatments without cover crops or with vetch increased when greater amounts of fertilizer were applied. Within individual fertility levels, higher celery yields were recorded in the oilseed radish plots. For example, in the low fertility rate, celery yield was 34.8, 29.2, 23.9, and 24.4 ton ha−1in the oilseed radish, cereal rye, hairy vetch, and control plots, respectively in 2003. Overall, the results of this experiment indicate that when included in a system where hoeing and hand-weeding are the only weed control methods, cover crops can successfully improve weed management and celery yield on muck soils, allowing reduced fertilizer inputs.

Energy flow for integrated apple production in Greece

Abstract Integrated production requires constant improvement of methods employed to achieve high fruit quality and yield with minimal inputs. This work was undertaken to evaluate the energy inputs for apple production, to identify the highest energy consuming operations and propose ways to improve them. Integrated production methods were employed during 1999 and 2000 at 26 apple (Malus domestica Borkh.) orchards in Zagora Pelion (Central Greece). The inputs and outputs of major nutrients (only five farms) as well as energy were calculated and mean values are presented. N inputs were five times higher than outputs and reduction in N fertilization can be considered. Total energy inputs were 50.7 GJ ha−1 and outputs 118.5 GJ ha−1 (51.6 GJ ha−1 from fruit). Chemicals (pesticides, fertilizers), use of machinery and fuel were the most important inputs for apple production, while human labor, although intensively used, accounted for small energy inputs due to conversion factor used. Energy outputs could be improved, as the potential for fruit production is higher compared to fruit production of the study years. Energy productivity was calculated (average of the 2 years) as 0.42 kg MJ−1, energy intensity as 2.50 MJ kg−1 and energy efficiency (only fruit considered) as 1.0. Thus, energy savings could be obtained without significant yield reduction, mainly through reducing fertilizer inputs (especially N), diminishing pest control applications through proper techniques and improving the farm road network.

Kentucky Bluegrass Response to Use of Aquatic Plants as a Soil Amendment

Rapid aquatic plant growth in Michigan's smaller lakes has reduced their navigability and recreational use. Harvested aquatic weeds have posed a new waste disposal issue for municipalities. Application of lake weeds as a soil amendment on area farms was viewed as a possible waste management option that might benefit local sod producers. The objectives of this study were to 1) estimate the amount of plant-available N (PAN) released from lake weed material, 2) determine the chemical composition of aquatic plant tissues and their effect on plant-available moisture, and 3) study turfgrass response to lake weed applications using the criteria of turfgrass quality, growth, and N uptake. Rates of lake weed refuse applied to field plots were 96, 161, and 206 Mg·ha-1. Two 47-day laboratory incubations were conducted with the same rates of refuse. Relative to biosolids, the metal content of the lake weeds was low and the nutrient content high. One megagram of lake weeds contained 0.37 kg of P and 2.5 kg of K. The decay constant for the C fraction in lake weeds was 8 to 10 days and 16 days for the N fraction. Estimates of the N supplied by lake weeds (570, 960, and 1200 kg PAN/ha) were based on data from C and N incubations. Application of lake weeds significantly increased plant-available soil moisture and significantly enhanced sod establishment and turf density, resulting in decreased weed pressure. However, excess N was present at higher application rates. Management concerns during the application of lake weeds should focus on nutrient loading and the timing of plant-available N release. Depending on methods of weed harvesting, we observed that large amounts of unwanted trash present in the plant biomass could discourage use by growers. Land application of lake weed refuse could ease waste disposal problems, reduce fertilizer inputs for sod growers, and improve the moisture status of sands. Further, this information can be of value to environmental regulatory agencies in determining safe and proper use of such waste materials.

Spatial Variability of Nutrient Requirements in Fields of the South Peace River Region, Alberta

Site-specific fertilizer application is pertinent only if there is a significant sub-field variability in nutrient requirements. The variability in soil test recommendations for nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) was measured, along transects across three fields in the South Peace River region of Alberta. Depending on the field and intended crop, site-specific fertilizer application would: (1) increase fertilizer inputs by 4–10 kg ha−1, (2) reduce fertilizer inputs by 5–30 kg ha−1, or (3) redistribute the same amount of fertilizer required for uniform application, differently among nutrients and across the field. Fields with extreme topography are more likely to benefit from site-specific fertilizer application, however, slope position alone would be inadequate to stratify fields for this purpose. Requirements for K were the most sensitive to sub-field variability, followed by those for S, P, and N. Producers in the region may not consider site-specific application because grid sampling may be too costly. Quick and economical ways to determine site-specific fertilizer requirements are needed.

Microbial communities in the phyllosphere of grasses on fenland at different intensities of management

AbstractThe effects of changes from conventional grassland management on fenland in Germany to extensification due to reduced fertilizer inputs and cutting frequency on the microbial colonization in the phyllosphere were investigated. A delay in the first cut for silage and hay, required by a nature conservation programme, was accompanied by the senescence of grasses which significantly influenced certain microbial groups. Heterotrophic bacteria, aerobic and anaerobic spore‐formers, as well as filamentous fungi, showed an increase in population densities on the mature herbage of the later cuts. Differences in the rate of fertilizer application and cutting frequency, which had an effect on the dry‐matter yield, also influenced the population density of heterotrophic bacteria and, in certain circumstances, that of filamentous fungi. Chemical measures of forage quality were highly correlated with the population density of microbial groups and with the maturity of the herbage. In contrast to these results, the population dynamics of further groups of micro‐organisms (yeasts, Micrococcaceae, listeria) did not show any relationship with pasture management.

Irrigated Tall Fescue–Legume Communities in the Southern Rocky Mountains

Short‐term testing of perennial forages may not determine their long‐term persistence and productivity. A study initiated in 1994 at New Mexico State University's Sustainable Agriculture Science Center at Alcalde was continued from 1998 to 2001, comparing irrigated monoculture tall fescue (Festuca arundinacea Schreb.) and tall fescue in binary mixtures with each of alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), cicer milkvetch (Astragalus cicer L.), or kura clover (Trifolium ambiguum M.B.) in three randomized complete blocks. Percentage of harvested grass in mixtures declined in midseason, but grass dry matter (DM) yield increased across the season. Grass DM yield averaged 7.78 and 4.79 Mg ha−1 yr−1 for the monoculture and mixtures, respectively. Seasonal distribution of kura clover and combined (kura + fescue) DM yield differed from other treatments causing year × harvest × treatment interactions. Cicer milkvetch–tall fescue performed poorly compared with the other treatments (mean annual yield 5.2 Mg ha−1). Mean annual yield (12.7 Mg ha−1) of the alfalfa–tall fescue mixtures was enough to enhance its usefulness over monoculture grass through reduced fertilizer inputs. The birdsfoot trefoil–tall fescue mixture also provided the benefit of reduced fertilizer requirements, but mean annual yield (8.2 Mg ha−1) equaled fertilized monoculture tall fescue. Kura clover–tall fescue average annual yields (14.1 Mg ha−1) equaled alfalfa–tall fescue. Stand longevity, reduced fertilizer inputs, and high yield and quality enhance the usefulness of kura clover in the southern Rocky Mountains. But, irregular seasonal distribution of kura clover between years may make forage budgeting difficult.

Effects of a Microbial Inoculant on Plant Growth and Rhizosphere Bacterial Populations of Container-grown Plants

A commercially available microbial inoculant (Plant Growth Activator Plus) that contains 50 microorganisms, primarily bacteria, was evaluated in a soilless container substrate to determine its effects on root bacterial populations and growth response of container-grown plants at three fertilizer rates. The tropical ornamental plants included hibiscus (Hibiscus rosa-sinensis `Double Red'), spathiphyllum (Spathiphyllum `Green Velvet') and areca palm (Dypsis lutescens). The bacterial groups enumerated were fluorescent pseudomonads, actinomycetes, heat-tolerant bacteria, and total aerobic bacteria. Analysis of the inoculant before its use determined that fluorescent pseudomonads claimed to be in the inoculant were not viable. The plant variables measured were plant color rating, shoot dry weight and root dry weight. Only hibiscus shoot dry weight and color rating increased in response to the addition of the inoculant to the substrate. Hibiscus roots also had a significant increase in the populations of fluores-cent pseudomonads and heat-tolerant bacteria. From a commercial production point of view, increasing fertilizer rates in the substrate provided a stronger response in hibiscus than did addition of the microbial inoculant. Furthermore, use of the inoculant in this substrate did not compensate for reduced fertilizer inputs.

Grassland management and nitrate leaching, a model approach

To calculate the effect of strategic, tactical and operational grassland management on nitrate leaching, the model Nitrogen, URine and Pastures (NURP) was developed. Data were collected and relationships developed between (i) herbage production, herbage N content and fertilizer input, (ii) N utilization by cattle and N intake, (iii) soil mineral N accumulation and non-harvested N from fertilizers and urine, and (iv) soil mineral N and nitrate concentration in the upper groundwater. Validation of the model shows good agreement with measured data from farms and monitoring programmes. Calculations show that even on dry sandy soils nitrate concentrations of 50 mg 1 −1 in the upper groundwater can be realized by a combination of restricted grazing during the growing season, housing earlier in the season and reduced fertilizer input. The effects of stocking rate, ratio dairy cows:young stock, milk production level, supplementary feeding, drought and urine scorch are discussed.

Efficient resource management in dairy farming on peat and heavy clay soils

Peat and heavy clay soils in the Netherlands are mainly used for permanent grassland to support dairy farming. As a result of intensification in dairy farming during the last decades, environmental quality is threatened by high emissions of N and P. Increased drainage of the wet soils has induced high mineralization rates, with associated losses of organic matter and nutrients. Improved utilization of N and P sources and new grazing and feeding strategies are proposed to reach environmental targets without loss of production. A sustainable prototype-system is designed by stepwise theoretical improvements of the current dairy farm. Although groundwater levels are kept high to limit breakdown of soil organic matter, the high availability of N and P from unavoidable peat mineralization offers the possibility to drastically reduce fertilizer inputs, which will directly reduce nutrient losses to the environment. Reduction of protein content in the ration reduces ammonia emission by approximately 20%, while milk production levels of 14,000 kg ha −1 per year can be maintained. The change from full to restricted grazing effectively reduces N losses from soil, but ammonia emission reductions are only significant with an improved slurry-application technique. A reduction in young stock reduces the roughage requirements but contributes little to the reduction of the nutrient surplus. Reduction of N imports trades off with the restoration of the soil-N stock, which is depleted by mineralization and unavoidable losses. Optimization of the utilization of nutrient resources is an effective first step to realize a sustainable fanning system.

Use of Cover Crop Mulches in a No-till Furrow-irrigated Processing Tomato Production System

No-till processing tomato (Lycopersicum esculentum Mill.) production in four winter cover crop-derived mulches was evaluated in 1997 and 1998 in Five Points, Calif. The effectiveness of two medics, `Sava' snail medic (Medicago scutellata Mill.) (sava), and `Sephi' barrel medic (Medicago truncatula Gaertn.) (sephi), and two cereal/legume cover crop mixtures, triticale/`Lana' woolypod vetch (X Triticosecale Wittm./Vicia dasycarpa Ten.) (triticale/vetch) and rye/`Lana' woolypod vetch (Secale cereale L./V. dasycarpa) (rye/vetch), was compared with two conventionally tilled fallow controls (with and without herbicide) (fallow+h and fallow-h) in suppressing weeds and maintaining yields with reduced fertilizer inputs. The comparison was conducted as a split plot, with three N fertilization rates (0, 100, and 200 lb/acre; 0, 112, and 224 kg·ha-1) as main plots and cover crops and fallow controls as subplots. Tomato seedlings were transplanted 3 weeks after the cover crops had been mowed and sprayed with herbicide. There were no significant differences in weed cover in the no-till cover crop treatments relative to the fallow controls in 1997. Early season weed suppression in rye/vetch and triticale/vetch plots was similar to herbicide-treated fallow (fallow+h) in 1998, however, later in the 1998 season weed suppression was best in the fallow+h. Tissue N was highest in the fallow treatments in both 1997 and 1998. Yields were highest in the triticale/vetch and fallow and lowest in sephi treatments in 1997, but there were no differences among treatments in 1998. These results demonstrate the feasibility of no-till mulch production of furrow irrigated processing tomatoes and identify opportunities for further optimization of the system.

Potassium Fertilization Effects on Alfalfa in a Mediterranean Climate

Potassium fertilization rates for alfalfa (Medicago sativa L.) have been increasing with intensive cropping systems or decreasing with policies that generally lead to reduced fertilizer inputs. In this case, nutrient buildup or maintenance of high soil test levels may not be desirable and drawdown of K reserves may be beneficial in the short term. The objective of this research was to evaluate the effects of potassium fertilization of alfalfa in areas of high soil exchangeable K levels and long growing seasons. A field experiment was established under irrigation from 1993 to 1997 in the Mediterranean environment of the Ebro Valley (Spain) on a silty clay loam soil. The treatments were five annual rates of K (0, 41.5, 83, 166, and 332 kg K ha−1) and two rates of K (166 and 332 kg K ha−1) applied prior to seeding on two alfalfa cultivars. The average annual dry matter (DM) yield was 21.5 Mg ha−1 and showed a small linear response to K fertilization (Pr > F = 0.0589). Total K removal in the herbage increased linearly with each rate of K and reached 1728 kg K ha−1 with the application of 332 kg K ha−1 yr−1, compared with 1546 kg K ha−1 without K fertilization. At the end of the experiment, soil ammonium acetate extractable K (Ke) increased little with K rates, and the differences were observed only in the first 30 cm of depth. Despite the uptake of 1546 kg K ha−1, soil Ke values did not change appreciably, suggesting that much of the K uptake was derived from the fertilizer and from nonexchangeable soil K fractions. Although K fertilization slightly increased alfalfa DM yields in this high testing Mediterranean soil, the economic benefit of this limited response does not justify the expense.

Influence of soil phosphorus status and nitrogen addition on carbon mineralization from 14 C-labelled glucose in pasture soils

This study examines the effect of soil P status and N addition on the decomposition of 14C-labelled glucose to assess the consequences of reduced fertilizer inputs on the functioning of pastoral systems. A contrast in soil P fertility was obtained by selecting two hill pasture soils with different fertilizer history. At the two selected sites, representing low (LF) and high (HF) fertility status, total P concentrations were 640 and 820 mg kg–1 and annual pasture production was 4,868 and 14,120 kg DM ha–1 respectively. Soils were amended with 14C-labelled glucose (2,076 mg C kg–1 soil), with and without the addition of N (207 mg kg–1 soil), and incubated for 168 days. During incubation, the amounts of 14CO2 respired, microbial biomass C and 14C, microbial biomass P, extractable inorganic P (Pi) and net N mineralization were determined periodically. Carbon turnover was greatly influenced by nutrient P availability. The amount of glucose-derived 14CO2 production was high (72%) in the HF and low (67%) in the LF soil, as were microbial biomass C and P concentrations. The 14C that remained in the microbial biomass at the end of the 6-month incubation was higher in the LF soil (15%) than in the HF soil (11%). Fluctuations in Pi in the LF soil during incubation were small compared with those in HF soil, suggesting that P was cycling through microbial biomass. The concentrations of Pi were significantly greater in the HF samples throughout the incubation than in the LF samples. Net N mineralization and nitrification rates were also low in the LF soils, indicating a slow turnover of microorganisms under limited nutrient supply. Addition of N had little effect on biomass 14C and glucose utilization. This suggests that, at limiting P fertility, C turnover is retarded because microbial biomass becomes less efficient in the utilization of substrates.

A Methodology for Precision Nitrogen Fertilization in High-Input Farming Systems

Nitrogen (N) emissions to ground and surface waters have become a major concern in many regions. In reaction, policy makers are tightening environmental constraints on agriculture, resulting in a call for more efficient management systems. This study presents a methodology for precision N fertilization in high-input farming systems applying split fertilizer strategies. Essentially, the method uses a mechanistic simulation model to quantify (i) soil mineral-N levels and (ii) N uptake rates on a real-time basis. Early warning signals are generated once N concentrations drop below a critical threshold level, indicating that additional fertilizer should be applied. Thresholds are not static, but defined in relation to actual uptake rates. Spatial variation is incorporated through the concept of management units: i.e., stable units with relatively homogeneous characteristics in terms of water regimes and nutrient dynamics. Separate simulations are conducted for each management unit, based on selected representative soil profiles. The proposed methodology was tested in a winter wheat (Triticum aestivum L.) field during the 1998 growing season. Six experimental strips were delineated receiving either ‘precise’ or traditional fertilization. Precision fertilization proved efficient in reducing fertilizer inputs (−23%), while slightly improving grain yields (+3%) and hectoliter weights (+4%). Results clearly illustrate the significance of precision management in the process of increasing fertilizer use efficiency.

The population dynamics of Anisantha sterilis in winter wheat: comparative demography and the role of management

Summary 1. We report on a 3‐year field study designed to monitor the detailed population dynamics of Anisantha sterilis in winter wheat, as well as to explore the consequences of changing broad‐scale patterns of management, in the form of reduced fertilizer inputs. 2. In the absence of herbicides, population dynamics were dominated by density‐dependent population growth. Unusually, this occurred mainly through density‐dependent recruitment. This was estimated to reduce population growth rates by 50‐fold, compared with the effects of density‐dependent competition between plants for resources. Density‐dependent recruitment also tended to buffer populations against year‐to‐year variations in emergence levels. 3. Little evidence for temporal variations in allometric seed production, the strength of competition between plants for resources or maximal mean plant performance was found in this study, or in comparison with previously published data. 4. No aspect of the life cycle was significantly affected by variation in the level of applied nitrogen fertilizer. In the case of competitive interactions we postulate that this lack of effect results from reduced intraspecific competitive effects as a consequence of decreased maximal plant size under low nitrogen conditions. The highly competitive nature of the environment in which A. sterilis occurs means that such changes tend to mask the effects of changing nitrogen levels. 5. Estimates of the effects of cultivation, on the other hand, indicated that seed germination, and hence population growth, was reduced by up to 90% when ploughing was employed rather than minimum tillage. While to some extent the effects of variation in the form of cultivation on population numbers may be buffered by density‐dependent recruitment, this effect outweighs any effects of nutrients or spatial or temporal variability in population dynamics. 6. Using previously published models for the dynamics of Alopecurus myosuroides, Avena sterilis and Avena fatua, we show that the response of populations of Anisantha sterilis to cultivation is very different from that of other grass weeds. In addition we show how single species models for population dynamics may be used to predict the responses of weed assemblages to changes in forms of management.

Use of spectral radiance for correcting nitrogen deficiencies and estimating soil test variability in an established bermudagrass pasture

The use of variable rate technology has become increasingly popular for applying plant nutrient elements. The most widely used method for determining variable fertilizer rates is presently based on soil testing and yield mapping. Three field studies (Bumeyville 1995, Burneyville 1996, and Ardmore 1996) were initiated in established Midland bermudagrass [Cynodon dacrylon (L) Pers.] pastures to determine the relationship between spectral radiance at specific wavelengths with forage nitrogen (N) removal and biomass, and to determine field variability of soil test parameters. Variable N (applied to 1.5 × 2.4 m subplots within 2.4 × 45.7 m main plots), fixed N and check treatments were evaluated at each location. Spectral radiance readings were taken in the red (671±6 nm), green (570±6 nm), and near infrared (NIR) (780±6 nm) wavelengths. The normalized difference vegetation index (NDVI) was calculated as NIR‐red/NIR+red. Variable N rates were applied based on NDVI. The highest fixed variable N rate was set at 224, 336, and 672 kg N ha‐1 for Burneyville, 1995, 1996, and Ardmore, 1996, respectively. At Bumeyville, soil samples were collected in all variable rate plots (1.5 × 2.4 m) and analyzed for various soil test characteristics. NDVI, red, green, and NIR spectral radiance readings were correlated with bermudagrass forage N removal and yield. Correlation of forage yield and N removal with red, NIR, and NDVI were best with maximum forage production, however, when forage production levels were low correlation decreased dramatically for the red wavelength compared with NIR and NDVI. Forage yield and forage N removal in variable rate treatments increased when compared to the check while being equal to the half‐fixed and fixed rates where higher N rates were applied. Also, variability about the mean in variable rate plots was significantly lower than half‐fixed and fixed rates which supports adjusting N rates based on indirect NDVI measurements. Variable N rate plots reduced fertilizer inputs by 60% and produced the same yield as fixed rate plots, while fixed and half‐fixed rates did not increase N content in the forage over that of the variable rate treatment. Soil sample data collected from small consecutive plots (<4 m2) was extremely variable indicating that intense sampling would be needed if variable fertilizer application were to be based on soil test results.

The effects of “starter” fertilizer injection on the growth and yield of drilled vegetable crops in relation to soil nutrient status

SummaryExperiments showed that injection of liquid NPK starter fertilizers directly below the seed of several vegetable crops enhanced early growth, and often increased yield at maturity, even on a soil of high PK status in the presence of ample broadcast fertilizer. Furthermore, small amounts of starter fertilizer applied to a low PK status soil increased early season growth of some crops to a level comparable with that on an adjacent fertile soil of the same soil series subject to identical cultural practices. In a separate experiment, yields from applying starter fertilizer alone on the low PK soil gave yields which were not significantly different from those obtained with much higher levels of conventional broadcast fertilizer. The inclusion of potassium in the starter solution was beneficial on the low K soil but generally had no effect in treatments with high levels of residual K, possibly because of an associated reduction of nitrogen in the starter as K increased. The growth response of seedlings on prepared gradients of residual soil P and K, with and without NPK starter fertilizer, varied with crop but suggests that little benefit from starter applications might be expected at levels >80 μg g–1 NaHC03-extractable P or >300 μg g–1 NH4NO3-exchangeable K (MAFF P indices >5 in the UK fertility classification, or K indices >3). It is suggested that the use of starter fertilizer offers scope for maintaining yields with reduced fertilizer inputs on soils at lower levels of residual nutrients than currently advised for conventional dressings.

Nitrate Leaching to a Shallow Mid-Atlantic Coastal Plain Aquifer as Influenced by Conventional No-Till and Low-Input Sustainable Grain Production Systems

In December, 1987, the states in the Chesapeake Bay region, along with the federal government, signed an agreement which called for a 40% reduction in nitrogen and phosphorus loadings to the Bay by the year 2000. To accomplish this goal, major reductions in nutrient loadings associated with agricultural management practices were deemed necessary. The objective of this study was to determine if reducing fertilizer inputs to the NT system would result in a reduction in nitrogen contamination of groundwater. In this study, groundwater, soil, and percolate samples were collected from two cropping systems. The first system was a conventional no-till (NT) grain production system with a two-year rotation of corn/winter wheat/double crop soybean. The second system, denoted low-input sustainable agriculture (LISA), produced the same crops using a winter legume and relay-cropped soybeans into standing wheat to reduce nitrogen and herbicide inputs. Nitrate-nitrogen concentrations in groundwater were significantly lower under the LISA system. Over 80% of the NT groundwater samples had NO3-N concentrations greater than 10 mgl-1, compared to only 4% for the LISA cropping system. Significantly lower soil mineral N to a depth of 180 cm was also observed. The NT soil had nearly twice as much mineral N present in the 90-180 cm portion than the LISA cropping system.

Growth Rate and Water Use by Legume Species at Three Soil Temperatures

AbstractLegumes may be used to reduce fertilizer inputs, provide ground cover for soil erosion protection, and reduce residual soil nitrates. Little data are available to guide a producer in selecting a legume that matches water and temperature conditions and produces acceptable growth and N2‐fixation rates. The purpose of the experiment reported here was to provide such information. After a 14‐d germination period at 20 °C, we grew eight legume species at soil temperatures of 10, 20, and 30 °C (± 2 °) for 105 d in a greenhouse. Daily water use was recorded, and plant dry weights were measured every 21 d. Initially annual species such as soybean [Glycine max (L.) Merr.] and fababean (Vicia faba L.) grew fastest at all temperatures. For the first 42 d at 10 °C, white clover (Trifolium repens L.), crimson clover (Trifolium incarnatum L.), and hairy vetch (Vicia villosa L.) also exhibited rapid growth. With warmer temperatures and longer growth periods, lespedeza (Lespedeza stipula L.) as well as soybean grew rapidly. At 20 and 30 °C, soybean growth was often more than double that of most other species. Growth was maximal at 10 °C for fieldpea (Pisum arvense L.), hairy vetch, and crimson clover; at 20 °C for fababean and white clover; and at 30 °C for soybean, sweetclover (Melilotus alba L.), and lespedeza. Average water‐use rates and water‐use efficiency generally paralleled growth, except water use increased and water‐use efficiency decreased as soil temperature increased. These results indicate that growth and water use differed greatly among legume species, that each legume species has its own characteristic optimum growth temperature, and that this optimum temperature for a given species may change as growth progresses.

Grain yield, stalk rot, and mineral concentration of fertigated corn as influenced by N P K

Abstract Peanut (Arachis hypoaaea L.) is a major cash crop in Georgia. Corn (Zea mays L.) is the preferred rotation crop, but is often not profitable because of large inputs costs. Fertilizer comprises approximately 50% of the variable production costs of irrigated corn. There is interest in reducing fertilizer inputs, in particular N, to reduce variable costs and decrease nitrate leaching to groundwater, but yields may suffer. Our objective was to investigate the effect of N, P, and K fertilizer rates on the yield of N‐fertigated corn in a corn/peanut rotation. Field experiments were conducted during 1987 and 1988 on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Paleudult) at Tifton, GA. Treatments were three rates each of N, P, and K fertilizer in a complete factorial. Nitrogen, P, and K rates were 168, 252, 336 kg N ha‐1 yr‐1; 44, 73, 103 kg P ha‐1 yr‐1; and 84, 223, and 363 kg K ha‐1 yr‐1, respectively. Grain yields were large, 12.6 and 10.4 Mg ha‐1 in 1987 and 1988, respectively, but n...