Elizabeth A. Guertal

TOMATO LEAF CHLOROPHYLL METER READINGS AS AFFECTED BY VARIETY, NITROGEN FORM, AND NIGHTTIME NUTRIENT SOLUTION STRENGTH

Abstract Leaf chlorophyll content is closely related to leaf nitrogen (N) content, so it is reasonable to assume that ammonium‐N (NH4‐N): nitrate‐N (NO3‐N) ratio in the nutrient solution used to grow tomatoes (Lycopersicon esculentum Mill.) hydroponically may affect leaf greenness, and consequently chlorophyll meter (SPAD) readings. It has also been shown that increasing nutrient solution strength (NSS) increases tomato productivity, but there are no reports regarding how NSS affects SPAD readings under greenhouse conditions. Genotype may also influence SPAD readings, and standardization for cultivar and sampling time may be needed. The objective of this study was to characterize SPAD readings for five tomato cultivars and SPAD reading response to a combination of two NSS (1X and 4X Steiner solution strength daily applied 18 days after transplanting at 7 p.m.) and two concentrations of NH4‐N in solution (0 and 25%) in order to evaluate the potential of SPAD readings as a tomato yield predictor in greenhouse production systems. The SPAD readings were not uniform across tomato varieties tested, being consistently higher for ‘Max’ and lower for the other varieties. Initially, SPAD readings for tomato varieties used in this study were low at the vegetative stage, and increased up to 40 DAT, but subsequently decreased at 49 DAT, or the fruit set of the first and second clusters. After this time, SPAD readings showed no variation. Chlorophyll meter readings for ‘Max’ were higher in the top plant layers, but decreased in the top plant layer of the other tomato varieties. The SPAD readings were higher for plants supplied with 25% NH4‐N than those without NH4‐N in solution, but the use of a nighttime nutrient solution did not affect SPAD readings. None of the possible interactions among tomato variety, NH4‐N: NO3‐N ratio, and NSS were consistently significant.

Influence of compaction from wheel traffic and tillage on arbuscular mycorrhizae infection and nutrient uptake by Zea mays

Interactive effects of seven years of compaction due to wheel traffic and tillage on root density, formation of arbuscular mycorrhizae, above-ground biomass, nutrient uptake and yield of corn (Zea mays L.) were measured on a coastal plain soil in eastern Alabama, USA. Tillage and soil compaction treatments initiated in 1987 were: 1) soil compaction from tractor traffic with conventional tillage (C,CT), 2) no soil compaction from tractor traffic with conventional tillage (NC,CT), 3) soil compaction from tractor traffic with no-tillage (C,NT), and, 4) no soil compaction from tractor traffic with no-tillage (NC,NT). The study was arranged as a split plot design with compaction from wheel traffic as main plots and tillage as subplots. The experiment had four replications. In May (49 days after planting) and June, (79 days after planting), root biomass and root biomass infected with arbuscular mycorrhizae was higher in treatments that received the NC,NT treatment than the other three treatments. In June and July (109 days after planting), corn plants that received C,CT treatment had less above-ground biomass, root biomass and root biomass infected with mycorrhizae than the other three treatments. Within compacted treatments, plants that received no-tillage had greater root biomass and root biomass infected with mycorrhizae in May and June than plants that received conventional tillage. Corn plants in no-tillage treatments had higher root biomass and root biomass infected with mycorrhizae than those in conventional tillage. After 7 years of treatment on a sandy Southeastern soil, the interactive effects of tillage and compaction from wheel traffic reduced root biomass and root biomass infected with mycorrhizae but did not affect plant nutrient concentration and yield. ei]J H Graham

Mapping of Soil Insect Infestations Sampled by Excavation and Acoustic Methods

Abstract Geostatistical analysis was used to map traditionally and acoustically sampled populations of soil invertebrates at two different times in a hayfield at Grove Hill, AL, and once in an Auburn, AL, hayfield. The distributions of nearly all the soil invertebrates and their sounds were nonrandom in all three mapping studies. The maps constructed by excavation and acoustic sampling methods were compared by correlating the estimated (kriged) soil invertebrate counts with the estimated (kriged) counts of sounds per minute (pulse rate). Acoustic and traditional estimates were positively correlated in the Auburn study. Kriged estimates for green June beetle grub counts overlapped significantly with kriged estimates of sound pulse rate (R2 = 0.47). Overlap with sound pulse rates increased slightly when other soil organisms were counted along with green June beetle grubs: estimates of sound pulse rates were significantly correlated with counts of all white grubs (R2 = 0.50), all white grubs with earthworms (R2 = 0.52), all white grubs with earthworms and earwigs (R2 = 0.59), and total invertebrates (R2 = 0.59). The correlation between acoustic and traditional estimates was not significant at Grove Hill in either year, possibly because of a lack of experience in signal analysis or because the soil invertebrates may not have generated enough sounds to be detected above the background noise levels. These results suggest that acoustic technology is a promising tool for detecting insect pests in soil, but that further study and additional analysis are needed to improve interpretation of acoustic data obtained in the field.

GREENHOUSE TOMATO RESPONSE TO LOW AMMONIUM-NITROGEN CONCENTRATIONS AND DURATION OF AMMONIUM-NITROGEN SUPPLY

High ammonium-nitrogen (NH4-N) concentration in solution may adversely affect greenhouse tomato (Lycopersicon esculentum Mill.) yield, but it has been reported that small NH4-N fractions improve yield and may increase vegetative growth and nutrient element uptake. The effects of short- or long-term supply of NH4-N to tomato plants is not clear, and further information is required to determine how it can affect fruit yield. The objective of this study was to determine the tomato yield response to 0:100, 10:90, 20:80, 30:70, and 40:60 NH4-N:NO3-N ratios supplied at the vegetative, vegetative plus flowering, flowering plus fruiting, and fruiting stages, and over the entire plant life cycle. Two experiments under greenhouse conditions were conducted with ambient light in which light intensity was 2,667 and 5,030 W h−1 m− 2 for the winter (1996–1997) and the spring (1997) experiments, respectively. In both experiments, neither the length of NH4-N supply nor the NH4-N concentration in solution affected tomato yield. Longer NH4-N supply increased the amount of fruit with blossom-end rot (BER) in the winter (1996–1997) experiment, but BER incidence was unaffected in the spring (1997) experiment by duration of NH4-N supply. The number of fruit with BER was greatly increased by higher NH4-N concentrations in solution in the spring (1997) experiment. Plant height was not affected by NH4-N concentration in either the winter or spring experiments, and neither was fruit firmness measured for fruit at the mature green stage. Fresh and dry weights were unaffected by NH4-N concentration or length of supply, but in the spring (1997) experiment, fresh weight of leaves, as well as their proportion to the weight of the aerial parts, were affected by both NH4-N concentration and length of supply. High concentrations of NH4-N and long periods of NH4-N supply increased calcium (Ca) concentration in leaf tissue, but only for the spring (1997) experiment was there a significant relationship between Ca concentration in leaves and BER incidence.

Nitrogen budget for fescue pastures fertilized with broiler litter in major land resource areas of the southeastern US

The southeast US produces a tremendous number of broiler chickens (Gallus gallus), which in turn produce massive quantities of litter (manure and bedding materials). In the Southeast, litter is most often disposed of via land application to pastures, however, the ultimate fate of much of the applied nitrogen (N) is not known. We have constructed N budgets for three sites across the southeastern U.S. in an effort to determine how much of the applied N is useful for plant production and how much is left to be absorbed by the environment. Study sites were located in the Coastal Plain (Alabama), Piedmont (Georgia), and Cumberland Plateau (Tennessee) Major Land Resource Areas (MLRA) of the southeastern US. Litter was applied in the Spring of two consecutive years at a rate to supply 70 kg of available N ha−1. The total amount of N applied ranged from 103 to 252 kg N ha−1 depending on site and year. Nitrogen fluxes monitored in this study were broiler litter N, ammonia (NH3) volatilization, denitrification, plant uptake, and leaching. Plant uptake represented the largest flux of applied N, averaging 43% of applied N. Losses due to NH3 volatilization and denitrification combined were only 6% of applied N on average. Loss of N due to NO3-N leaching appeared to be significant only at the Coastal Plain site where NO3-N concentrations in the groundwater peaked at 38 mg N l−1. We believe the majority of excess N shown in these budgets is likely accounted for by leaching losses and soil accumulation. Regardless of these assumptions and low gaseous losses, it is apparent that on average, 57% of applied N is destined for a fate other than plant uptake. The results of this study indicate that land-application of broiler litter at currently recommended rates has the potential for negative impacts on the environment of the southeastern U.S. in the long-term.

Effects of nitrogen form, nighttime nutrient solution strength, and cultivar on greenhouse tomato production

Abstract Higher greenhouse tomato (Lycopersicon esculentum Mill.) yield is obtained by using 25% of NH4‐N in solution compared to using NO3‐N as the sole nitrogen (N) source. However, blossom‐end rot (BER) may occur in tomato fruit when NH4‐N was present in nutrient solutions. High nutrient solution strengths improve tomato fruit quality, but can also increase BER. Two NH4‐N concentrations in solution (0 and 25%), and two nighttime solution strengths (NSS) (1X and 4X Steiner solution strength applied at 7 p.m.) were used to grow five indeterminate type greenhouse tomato cultivars: Caruso, Jumbo, Match, Max, and Trust. A significant interaction occurred between NH4‐N concentration and NSS factors: 0% NH4‐N and high NSS increased marketable yield and fruit:whole plant ratio, and reduced BER. In contrast, a concentration of 25% NH4‐N and high NSS reduced marketable yield and the fruit:whole plant ratio, and increased BER incidence. Max, Match, and Trust tomato cultivars produced high marketable yield and hig...

Ammonium concentration in solution affects chlorophyll meter readings in tomato leaves

Abstract Combinations of NH4‐N:NO3‐N usually result in higher tomato (Lycopersicon esculentum Mill.) yields than when either form of nitrogen (N) was used alone. Leaf chlorophyll content is closely related to leaf N content, but the effect of the NH4‐N:NO3‐N ratio on leaf greenness was not clear. The objective of this study was to determine the influence of NH4‐N:NO3‐N ratios on chlorophyll meter (SPAD) readings, and evaluate the meter as a N status estimator and tomato yield predictor in greenhouse production systems. Fruit yield and SPAD readings increased as the amount of NH4‐N in solution increased up to 25%, while higher ratios of NH4‐N resulted in a decline in both. The N concentration in tomato leaves increased as concentration of NH4‐N in solution increased. Fruit yield increased as chlorophyll readings increased. SPAD readings, total N in leaves, fresh weight of shoots, and fruit yield all showed a quadratic response to NH4‐N, reaching a peak at 25 or 50% of N as NH4‐N. SPAD readings taken at the...

Nitrogen rate and within-row plant spacing effects on sweetpotato yield and grade

Abstract A 2‐yr study was conducted to evaluate the effect of within‐row spacing and nitrogen (N) fertility on sweetpotato [Ipomoea batatas (L.) Lam.] yield and quality. Conducted in North Alabama on a Hartsells fine sandy loam (fineloamy, siliceous, thermic Typic Hapludult), the study consisted of four replications of a factorial arrangement of four within‐row spacings (15, 20, 25, and 30 cm) and 4 N fertility rates (0, 36, 72, and 108 kg N/ha). Nitrogen fertilization did not affect yield or quality of harvested storage roots and there was no significant interaction between row spacing and N rate in either year. In 1994, greatest total yield ofsweetpotatoes occurred with the narrowest within‐row spacing (15 cm), but in 1995 within‐row spacing did not affect total yield. In 1994, as within‐row spacing increased, yield of Jumbo sweetpotatoes increased.

EFFECTS OF SOIL FUMIGATION AND N SOURCE ON SOIL INORGANIC N AND TOMATO GROWTH

Soil fumigation, commonly used in vegetable production, may alter the rate of nitrification, affecting availability of N for crop use. The objective of this research was to examine effects of soil fumigation and N fertilizer source on tomato growth and soil NO3–N and NH4–N in field production. Experiments 1 and 2 included application of methyl bromide at 420 kg ha-1 to a Norfolk sandy loam (fine loamy siliceous thermic Typic Kandiudult) in combination with preplant applications of calcium nitrate, ammonium nitrate, and ammonium sulfate at 144 kg N ha-1. An additional fumigant, metam-sodium, was included in the second experiment at 703 L ha-1 (268 kg sodium methyldithiocarbamate ha-1). Experiment 3 included methyl bromide and metam-sodium, with ammonium sulfate as the sole source of N applied at 144 kg N ha-1. In the first two studies, fumigants had little or no effect on soil NH4–N or NO3–N concentration. Tomato plants were larger and fruit yield was greater in fumigated plots, but there were few growth or yield responses to N source. In the third experiment, fumigants increased concentration of soil NO3–N and NH4–N at 16 days after fumigation (DAF), however, there was no effect on nitrification owing to fumigants. It appears that N source selection to overcome inhibition of nitrification is not necessary in plant production systems that involve fumigation

Nitrogen mineralization from ‘AU Golden' sunn hemp residue

ABSTRACT The tropical legume sunn hemp (Crotalaria juncea L.) cultivar ‘AU Golden’ has the potential to provide substantial nitrogen (N) to subsequent crops to reduce recommended application rates of synthetic N fertilizers. A mineralization field trial was conducted to measure mass decomposition and N and carbon (C) amounts remaining from sunn hemp residue following three planting dates (May, June, and July) during the 2013 growing season at the Tennessee Valley (TVS) and Coastal Plain (WGS) locations of AL. Residue from June and July plantings contained 50.0% and 61.1% N at WGS and 41.5% and 66.5% N at TVS by the end of their respective incubation periods compared to residue from the May planting, which contained 21.1% N at WGS and 47.8% at TVS. In order to create a more synchronous relationship between ‘AU Golden’ residue N mineralization and crop demand, termination must be delayed until approximate planting of the following crop.