Thermic Plinthic Kandiudults Research Articles

POD YIELD AND KERNEL SIZE DISTRIBUTION OF PEANUT PRODUCED USING SUBSURFACE DRIP IRRIGATION

Longterm yield data are essential to determine the economic feasibility of installing a subsurface drip irrigation(SDI) system for crop production. However, first year yields and associated economic returns are vital for system paymentthe first year. Vegetable and row crop production has been successful with SDI, but pod yield and kernel size distribution dataon peanut (Arachis hypogaea L.) are limited especially during the installation year. Site 1 was established in 1997 on aFaceville sandy loam soil (fine, kaolinitic, thermic Typic Kandiudults) converted from native grass pasture. Site 2 wasestablished in 1998 on a Tifton sandy loam soil (fineloamy, kaolinitic, thermic Plinthic Kandiudults) following two yearsof cotton. These SDI systems include two lateral spacings (0.91 and 1.83 m) buried at 0.3 m soil depth. Site 1 had two emitterspacings (46 and 61 cm) and two irrigation levels. Site 2 had one emitter spacing (46 cm) and three irrigation levels. Anonirrigated (NI) control was included at each site. Irrigation water was applied daily based on estimated ETo whereirrigation level one (IL1) was ETo *Kc, and IL2 and IL3 were 75 and 50% of IL1, respectively. Pod yield increased 38% withSDI (5433 kg ha 1 ) compared to NI peanut (3937 kg ha 1 ). When compared to the state average (3012 kg ha 1 ), SDI showeda 81% pod yield increase. The percentage of jumbo kernels increased 39% at Site 1 and 81% at Site 2 compared with NI. SDIpeanut had lower quantity (75% less) of number one sized peanut kernels than NI. Overall, during the installation year, SDIhad higher pod yields and larger kernel size than NI treatments. These yield data can be useful when projecting the economicfeasibility of installing a SDI system and making the first year payment.

GLEAMS, Opus, PRZM2β, and PRZM3 Simulations Compared with Measured Atrazine Runoff

High‐intensity storms that occur shortly after chemical application have the greatest potential to cause chemical runoff. We examined how effectively current chemical transport models GLEAMS, Opus, PRZM2β, and PRZM3 could predict water runoff and runoff losses of atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] under such conditions, as compared with observations from a controlled field runoff experiment. The experiment was conducted for 2 yr using simulated rainfall on two 14.6‐ by 42.7‐m plots within a corn (Zea mays L.) field on Tifton loamy sand (fine‐loamy, kaolinitic, thermic Plinthic Kandiudults) under conventional tillage practices. For each plot‐year, atrazine was applied as surface spray immediately after planting and followed by a 50‐mm, 2‐h simulated rainfall 24 h later. A similar preapplication rainfall and four subsequent rainfalls during the growing season were also applied. Observed water runoff averaged 20% of the applied rainfall. Less runoff occurred from freshly tilled soil or under full canopy cover; more runoff occurred when nearly bare soil had crusted. Observed total seasonal atrazine runoff averaged 2.7% of that applied, with the first posttreatment event runoff averaging 89% of the total. GLEAMS, Opus, PRZM2β and PRZM3 adequately predicted water runoff amounts, with normalized root mean square errors of 29, 29, 31, and 31%, respectively. GLEAMS and PRZM3 predicted atrazine concentrations in runoff within a factor of two of observed concentrations. PRZM2β overpredicted atrazine concentrations. Opus adequately predicted atrazine concentrations in runoff when it was run with an equilibrium adsorption submodel, but significantly underestimated atrazine concentrations when it was run with a kinetic sorption submodel.

Total and Seasonal Distribution of Dry Matter Yields for Pearl Millet × Wild Grassy Subspecies Hybrids

The wild grassy subspecies Pennisetum glaucum (L.) R. Br. subspecies monodii (Maire) Brunken has been used as a source of germplasm for improved disease resistance and cytoplasmic diversity for improving pearl millet [P. glaucum (L.) R. Br.] cultivars. The objective of this research was to evaluate a portion of the monodii germplasm to determine if this germplasm could be used to increase the dry matter yield and extend the growing period of pearl millet forage hybrids. Seventy‐nine monodii accessions from Niger, Mali, Senegal, and Burkina Faso were crossed with Tift 85DA1, a cytoplasmic‐nuclear‐male‐sterile (CMS) pearl millet used in commercial hybrid production. These hybrids along with `Tifleaf 2' (a popular commercial hybrid) and `Gahi 3' were tested for 2 yr on a fine, loamy, thermic Plinthic Kandiudult soil at Tifton, GA, latitude north 31.48° and longitude west 83.53°. The best experimental hybrid yielded up to 31% more dry matter than Tifleaf 2. A significant hybrid × year effect on total yield indicated that some of the hybrids showed a differential response during the 2 yr. Tifleaf 2 produced between 23 and 32% of its total yield in the last harvest, whereas a number of the experimental hybrids produced significantly more (up to 50%) of their dry matter in the last harvest. The experimental hybrids were consistent across years in their superior late‐season production. Variation was also observed among hybrids for production of dry matter in the first harvest. Early production would be especially valuable in areas that have distinct wet and dry seasons. This research indicates that genes for enhancing level and distribution of yield in cultivated pearl millet are present in the wild grassy subspecies, monodii

Agronomic and Economic Analyses of Cotton Starter Fertilizers

None of the published literature has focused on the response of cotton (Gossypium hirsutum L.) to various starter fertilizer sources. This study was conducted to determine (1) if cotton grown on Coastal Plain soils in South Georgia would respond to different starter fertilizer sources and (2) if use of starter fertilizers would result in an economic gain. Experiments were conducted in 1997 and 1998 at the Coastal Plain Experiment Station in Tifton on a Tifton loamy sand (fine‐loamy, kaolinitic, thermic Plinthic Kandiudults), the Southeast Georgia Branch Station in Midville on a Dothan loamy sand (fine‐loamy, kaolinitic, thermic Plinthic Kandiudults), and the Southwest Branch Experiment Station in Plains on a Greenville sandy clay loam (fine, kaolinitic, thermic Rhodic Kandiudults). Five starter fertilizer sources were applied 5 cm to the side of and 5 cm below the seed drill at planting in each study. Total shoot N and Ca were increased in two of the six studies with starter fertilizers. Likewise, plant height, leaf area index, and shoot dry weight was increased with starter fertilizers in two of the six studies. With the exception of micronaire, starter fertilizers did not significantly influence the fiber properties investigated. Differences in fiber properties did result in small differences in cotton price premiums or discounts. Lint yields were significantly increased with starter fertilizers at Midville and Plains in 1997, when the crop was exposed to an extended period of cool weather immediately after planting. The most appropriate cotton starter fertilizer appeared to depend on soil type.

Analysis of Cotton Yield Stability Across Population Densities

Final lint yield in cotton (Gossypium hirsutum L.) is relatively stable across a wide range of population densities. This study was conducted to determine (i) which components of final lint yield impart this yield stability across plant populations and (ii) how yield distribution is influenced by population density. Studies were conducted in 1997 and 1998 on a Tifton loamy sand (Fine‐loamy, kaolinitic, thermic Plinthic Kandiudults). Cotton was planted in each study on 91‐cm row widths at seeding rates ranging from 3.5 to 25.1 seeds m−2. At harvest, each plot was hand picked and boll numbers and weights were recorded at each monopodial branch and sympodial branch fruiting position. Lower population densities led to plants with more mainstem nodes and monopodial branches with increased fruit retention, resulting in greater fruit production per plant. Boll size was inversely related to population density. Mean net assimilation rate from first flower to peak bloom also was related inversely to population density. The mainstem node of peak boll set increased with population density. Fruit production on a ground area basis was greater in the first sympodial position as population density increased, while fruit production on a ground area basis in third positions and monopodial branches was greater as population density decreased. Accumulative seedcotton from sympodial branches also increased with population density. Total fruit number and seedcotton yield per area were not influenced by population density in these studies. Yield stability across population densities was achieved through manipulation of boll occurrence and weight.

Nitrate‐Nitrogen, Soluble, and Bioavailable Phosphorus Runoff from Simulated Rainfall After Fertilizer Application

AbstractRunoff from crop land can enhance eutrophication of fresh water and hypoxia in sea water. We simulated rain at 25 mm hr‐1 for 2 hr, 8 d prior and 1, 14, 29, 49 and 108 d after fertilization and planting of corn (Zea mays L.). Experimental sites received 50 kg N, 45 kg P, and 125 kg K ha‐1 as granulated fertilizer broadcast and incorporated to a depth of 150 mm. An additional 118 kg N ha‐1 was surface‐banded as solution fertilizer at Day 28, which was 1 d prior to the Day 29 rain. The study was conducted for 2 yr on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudults) with a slope of 4.5%, on micro‐ (5.57 m2) and meso‐scale (622 m2) plots. Runoff was equal for the two scales of plots. There were greater runoff losses of soluble‐P from meso‐ (1.4 kg ha‐1) than from micro‐plots (1.0 kg ha‐1). Nitrate‐N losses averaged 2.7 kg ha‐1 and bioavailable‐P losses were 2.3 kg ha‐1. Greatest NO3‐N and soluble‐P losses occurred the day after application of the soild fertilizer, whereas bioavailable‐P loss was greatest at Day 14 and 29. No increase in NO3‐N losses was found 1 d after the application of urea ammonium nitrate solution, possibly indicating that liquid fertilizers are not as susceptible to runoff losses as solid fertilizers. Results of this study should encourage the use of small plots, thereby saving research time and expense and provide data useful for estimating losses at similar sites.

TEMPORAL DISTRIBUTION OF 14C IN SOIL WATER FROM FIELD LYSIMETERS TREATED WITH 14C-METOLACHLOR

In a previous study utilizing fallow field lysimeters of an undisturbed, loamy sand soil treated with 14 C-metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], 2 to 5% of the applied 14 C was mobile to soil depths of 56 to 96 cm. The objective of this 120-day study was to determine the temporal distribution of 14 C-metolachlor and/or metabolite(s) in soil water from similar field lysimeters and their possible contribution to groundwater contamination. Undisturbed soil column field lysimeters (20.3-cm i.d. × 101-cm long; 16 gauge steel) were driven into a conventionally tilled Dothan loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) and treated with 14 C-metolachlor and tritiated water ( 3 H 2 O) and subjected to natural rainfall or irrigation. Percent recovery of metolachlor and/or metabolite(s) in the soil, as based on 14 C measurement, was 62% at 30 days, 63% at 60 days, 51% at 90 days, and 49% at 120 days. Recovery of 3 H 2 O was 36, 24, 6 and 0.25% of the applied for the same time periods. By 30 and 60 days after application (DAA), 3 H 2 O had distributed symmetrically in the soil profile, whereas, a large percentage of the 14 C was retained in the upper 24 cm. No 14 C and <1% of the applied 3 H 2 O was recovered in leachate the first 30 days. Cumulative recovery of 14 C in leachate was <1% of that applied at 60 days, 3% at 90 days, and 7% at 120 days. Cumulative recovery of 3 H 2 O in leachate for the same time periods was 22, 39, and 39% of that applied. The symmetrical breakthrough curve for 3 H 2 O indicated no preferential flow or immobile water, whereas the breakthrough curve for 14 C was asymmetrical as a result of the sorption-desorption processes. Peak concentrations of 14 C and 3 H 2 O in the leachate occurred at 94 and 63 DAA, respectively. The sorptive tendencies of both radiolabeled species distinguished the magnitude of movement, with 3 H 2 O much more mobile than 14 C-metolachlor and/or metabolite(s). Assuming that all 14 C in leachate was parent, average metolachlor concentrations in leachate were less than the National Health Advisory level, which may indicate that metolachlor should be considered a low risk chemical because of its potential to contaminate groundwater in soils with low organic matter and high clay content in the subsoil.

Fiber Yield and Quality of Cotton Grown at Two Divergent Population Densities

Poor seed germination and early seedling damage often reduce plant populations in the north‐eastern cotton (Gossypium hirsutum L.) producing region of the USA. A field study was conducted at Clayton, NC, on a Dothan sandy loam (fine‐loamy, siliceous, thermic Plinthic Kandiudult) to investigate responses of cotton reproductive development to reduced plant population. All flowers on plants grown at 2 and 12 plants m−2 were tagged so that associations among boll and lint quantity and quality, flowering date, and fruiting position could be determined. On plants grown at 2 plants m−2, 33 and 65% of their fiber came from flowers initiated before 88 days after planting (DAP) in 1992 and 1993, respectively. Plants grown at 12 plants m−2 produced 63 and 88% of their fiber from flowers initiated before 88 DAP in 1992 and 1993, respectively. Plant population did not affect total lint yield, however. Because of favorable late‐season weather, plants grown at 2 plants m−2 produced more bolls on vegetative branches and at more distal sympodial positions than did plants grown at 12 plants m−2. Boll weight and micronaire were generally higher for earlier bolls at all positions for the lower population density. Later bolls exhibited poorer boll and fiber properties, indicating negative effects of reduced heat unit accumulation by later bolls. Our findings indicate that replanting, which might delay stand establishment by 3 to 4 wk, would be of little help toward improving fiber yield because it would rely more heavily on later produced bolls.

Establishment of ‘Tifton 9’ Bahiagrass in Response to Planting Date and Seed Coat Removal

AbstractStands of ‘Tifton 9’, like those of other bahiagrasses (Paspalum notatum Flügge var. saurae Parodi), develop slowly. Our objectives were to determine seedling emergence and stand establishment responses to planting date and mechanical seed coat removal using greenhouse and field plantings. Seed dehulled by acceleration in an airstream to hit a metal plate (7.8 kg ha−1) or whole seed (11.2 kg ha−1) was planted at equivalent rates in five blocks of a randomized complete block design on seven biweekly planting dates from 9 March through 1 June in 1994 and 1995 at both a droughty upland site (Dothan loamy sand: fine‐loamy, siliceous, thermic Plinthic Kandiudults) and a lowland site (Alapaha sand: loamy, siliceous, thermic Arenic Plinthic Paleaquults) near Tifton, GA (31°26′ N, 83°35′ W), to observe emergence and establishment. Spring and fall plant counts and final stand ratings of percent bahiagrass occurrence were used to evaluate emergence and establishment. Emergence 7 d after greenhouse planting of dehulled seed (18.3%) was greater (P &lt; 0.01) than whole seed (0.7%). Emergence at 28 d after planting was not different (36.2%) between seed treatments. Mean surface (0 to 50 mm) soil moisture content at the lowland site (58 g kg−1) was higher than the upland site (28 g kg−1). Seedling heights, measured in June 1994, spring seedling number in both years, and 1995 fall plant numbers were often higher with earlier planting date. No differences in final stand (% occurrence) could be attributed to planting date. Final stand ratings were greater (P &lt; 0.05) at the lowland (84%) than at the upland site (79%), and greater (P &lt; 0.05) for whole than for dehulled seed in 1994, but no differences were observed in 1995. Development of Tifton 9 bahiagrass stands at these Coastal Plain sites was slow, but relatively insensitive to differences in spring or early summer planting date. Dehulled seed emerged more rapidly, but this provided no sustained advantage in stand establishment in these environments.

Influence of tractor wheel tracks and crusts/seals on runoff: Observations and simulations with the RZWQM

In simulations on the fate of agricultural chemicals applied to crops, accurate partitioning of rainfall between infiltration and runoff is fundamental to chemical runoff predictions. We evaluated the Root Zone Water Quality Model (RZWQM version 3.1) against measured runoff from two field plots (15×45 m with 3% slope) on a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult). Six simulated rainfall events, each 25 mm h −1 for 2 h, were applied to maize ( Zea mays, L.) each year. In the uncalibrated mode, RZWQM under-predicted runoff by 40% on average, with the closest fit for events that occurred after full canopy. Saturated hydraulic conductivity ( Ks) accounted for the majority of the uncertainty in predicted runoff. When Ks of the surface crust was back calibrated from the measured runoff, RZWQM predicted runoff closely for the remaining plots and events. Alternatively, using different Ks values for wheel track and crop beds, running the model for each and, then, proportionally assigning runoff also led to predictions that agreed with measured runoff. When spatial and temporal changes in Ks were calibrated to specific conditions at the site, RZWQM effectively predicted runoff.

SIZE OF POINTERS FOR RESIDUE COVER MEASUREMENT

Comprehensive models for agrichemical transport necessarily include runoff predictions to partition rainfallbetween infiltration and runoff, as this ability is fundamental to predictions of chemical runoff and leaching. We compared GLEAMS, Opus, and PRZM-2 model runoff predictions with runoff measured in a precisely controlled field site used for chemical runoff studies. In 1992 and 1993, two 14.5 m 42.9 m corn (Zea mays, L.) field plots with 3% slope on Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) received six severe, artificial rainfall events over the growing season with each event consisting of a 25 mm hC1 rainfall for 2 h. Runoff was monitored continuously using a collector and flume. Model performance criteria included sensitivity analysis, graphical comparison and statistical analysis including mean, ratio of means, root mean square error (RMSE), and a paired difference t-test. Observed runoff averaged 20% of added rainfall. Lowest values occurred with freshly plowed soil or full canopy cover, while 24 to 34% runoff occurred when nearly bare soils had crusted over. Using an initial moisture condition-II curve number (CN) of 85, GLEAMS and Opus predicted runoff within 10%, overall, and produced a pattern of high and low runoff that closely followed observed. PRZM-2 overpredicted runoff by 90%, overall, and predicted its highest runoff when observed runoffwas lowest. Paired difference t-tests indicated a significant difference between measured and predicted runoff for PRZM-2 (p<0.001 at = 0.05), but none for GLEAMS (p = 0.761) or Opus (p = 0.194). Mean, ratio of means, and RMSE showed that GLEAMS and Opus performed better than PRZM-2. All three models were very sensitive to CN values which were empirical and subjective, but less sensitive to measurable soil physical properties. With careful parameterization, GLEAMS and Opus could be used to simulate runoff from similar row-crop and soil conditions.

GLEAMS*, OPUS, AND PRZM-2 MODEL PREDICTED VERSUS MEASURED RUNOFF FROM A COASTAL PLAIN LOAMY SAND

Comprehensive models for agrichemical transport necessarily include runoff predictions to partition rainfallbetween infiltration and runoff, as this ability is fundamental to predictions of chemical runoff and leaching. We compared GLEAMS, Opus, and PRZM-2 model runoff predictions with runoff measured in a precisely controlled field site used for chemical runoff studies. In 1992 and 1993, two 14.5 m 42.9 m corn (Zea mays, L.) field plots with 3% slope on Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) received six severe, artificial rainfall events over the growing season with each event consisting of a 25 mm hC1 rainfall for 2 h. Runoff was monitored continuously using a collector and flume. Model performance criteria included sensitivity analysis, graphical comparison and statistical analysis including mean, ratio of means, root mean square error (RMSE), and a paired difference t-test. Observed runoff averaged 20% of added rainfall. Lowest values occurred with freshly plowed soil or full canopy cover, while 24 to 34% runoff occurred when nearly bare soils had crusted over. Using an initial moisture condition-II curve number (CN) of 85, GLEAMS and Opus predicted runoff within 10%, overall, and produced a pattern of high and low runoff that closely followed observed. PRZM-2 overpredicted runoff by 90%, overall, and predicted its highest runoff when observed runoffwas lowest. Paired difference t-tests indicated a significant difference between measured and predicted runoff for PRZM-2 (p<0.001 at = 0.05), but none for GLEAMS (p = 0.761) or Opus (p = 0.194). Mean, ratio of means, and RMSE showed that GLEAMS and Opus performed better than PRZM-2. All three models were very sensitive to CN values which were empirical and subjective, but less sensitive to measurable soil physical properties. With careful parameterization, GLEAMS and Opus could be used to simulate runoff from similar row-crop and soil conditions.

Subsoil Nitrate Uptake by Grain Pearl Millet

AbstractPearl millet [Pennisetum glaucum (R.) Br.] is a high‐quality grain crop that can that can be grown without irrigation during hot, dry summers in the southeastern United States. The N rate required for optimum pearl millet grain yield varies widely in published studies, possibly because of variability in residual soil N from the subsoil. Field studies were conducted in the southern Coastal Plain at Tifton, GA, on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudult) with nitrate accumulations near subsoil plinthite. The objective was to determine if pearl millet can extract N from acidic, relatively impermeable subsoils. Nitrate N (1 M KCl‐extractable) was 4 mg kg−1 in the surface 0.6 m, 1 mg kg−1 in the next 0.6 m, and 6 mg kg−1 from 1.2 to 1.5 m. We fertilized pearl millet field plots with two levels of N (0 and 168 kg ha−1) and studied root development during the growing seasons in 1993 and 1994. Soil cores were taken 40 d after planting to a depth of 1.2 m, separated into 0.3‐m depth segments, and root length density was measured. Roots were found in the deepest segments. Nitrogen fertilization increased the proportion of the root length density found in the surface soil in one year. We also injected 15N as 60% atom l5N‐enriched KNO3 at a depth of 1 m at 30 and 40 d after planting. At physiological maturity, atom % 15N abundance in the plants ranged from 10.1 to 12.0 where 15N was injected and was near natural abundance where no 15N was injected. These results indicate that pearl millet can extract N from 1 to 1.2 m in an acidic and impermeable subsoil.

COMPARISON OF INSTANTANEOUS EQUILIBRIUM AND EQUILIBRIUM-KINETIC SORPTION MODELS FOR SIMULATING SIMULTANEOUS LEACHING AND RUNOFF OF PESTICIDES1

Two chemical sorption models, a two-site equilibrium-kinetic sorption model (E-K) and an instantaneous equilibrium sorption model (I-E), were used to describe pesticide leaching and runoff. Concentrations of bromide, atrazine, and fenamiphos in leachate and runoff water from 1.0 m × 0.5 m × 0.1-m boxes of packed air-dry Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudults) were compared with simulated concentrations predicted by the Root Zone Water Quality Model (RZWQM). Atrazine and bromide (as KBr) were applied to the soil surface and fenamiphos was incorporated into the top 7 cm. Water (100 mm in 2 h) was applied using sprinkler rainfall simulator 24 h later. The E-K model and the I-E model, which are the two submodels for chemical sorption in RZWQM, were used for pesticide sorption simulations, and a nonuniform mixing model was used for pesticide runoff simulations. Model parameter values were obtained by measurements, from the literature, and by calibration with measured atrazine and fenamiphos breakthrough curves (BTCs) and a runoff chemograph from an independent experiment. Results showed that the E-K model simulated atrazine and fenamiphos leaching and atrazine runoff better than the I-E model. The I-E sorption model underestimated pesticide leaching and overestimated atrazine runoff. Compared with previous studies showing that the E-K model simulated pesticide sorption and leaching better than the I-E sorption model with initially saturated soils and under steady state water flow conditions, this study showed that the E-K model also worked better than the I-E sorption model for initially air-dry soil and under fast and transient water flow conditions for leaching as well as runoff of a pesticide.

Long-Term Phosphorus and Potassium Application to Corn on Coastal Plain Soils

The effect of long-term fertilizer applications on soil test levels, yield, and crop removal depends on soil texture and mineralogy. The objectives of this study were to measure the fluctuations in soil P and K in soils of varying texture and to evaluate the usefulness of the Mehlich-1 soil extractant in predicting yield response. A field experiment was conducted for 11 yr on two soils : a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudults) and a Greenville sandy clay loam (clayey, kaolinitic, thermic Rhodic Kandiudults). Phosphorus treatments were 0, 92, 183, and 275 lb P 2 O 5 lb/acre in the first year followed by annual applications of 0, 37, 73, and 0 lb/acre, respectively. Potassium treatments were 0, 48, 96, and 144 lb K 2 O/acre in the first year followed by annual applications of 0, 48, 96, and 0 lb/acre, respectively. Soil samples (0-6 in.) were collected each year at tasseling of the corn (Zea mays L.) crop, P and K concentrations were determined in soil and grain samples, and yield was measured. Initial application rates influenced initial soil test levels, and annual application rates affected the rate of change of soil test levels with time. All significant yield increases on the Greenville soil were due to P application. Phosphorus moves rapidly from solution into less available forms in the Greenville soil due to the soil's high P fixing capacity. Yield increases on the Tifton soil resulted from K applications, presumably due to greater leaching losses on the sandier textured soil. The Mehlich-1 extractant provides a questionable measure of soil P availability for corn. Particularly in areas where P runoff potential is high, P fertilizer should not be applied to irrigated corn in the Southeast unless the Mehlich-1 extractable soil P concentration ≤ 12 lb/acre. Data from this long-term study show that accounting for soil K below the plow layer may improve the use of mehlich-1 extractant as a measure of K availability for corn.

Nitrogen Mineralization and Ammonia Volatilization from Fractionated Poultry Litter

AbstractPassing poultry litter through a 0.83‐mm sieve generates a fine fraction higher in N concentration and cheaper to transport per unit of N than the whole litter. One objective of this work was to determine if the organic N in the fine fraction undergoes faster mineralization than that in the whole litter. Whole litter or fine fraction from three poultry houses was either mixed with samples of Dothan loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudult) or applied on the soil surface at a rate of 100 kg N ha−1. The treatments were incubated at water field capacity and 27°C, with samples extracted at 3, 7, and 14 d. Differences in N mineralization were relatively small between materials; by Day 14, the organic N had undergone a slightly higher mineralization in the fine fraction (51.5%) than in the whole litter (44.5%). A second objective was to compare the potentials for net N mineralization, NH3 volatilization, and respiration of whole poultry litter and fine fraction stored for 7 d at 25 °C and at two water contents (unamended [0.12–0.26 kg H2O kg−1] and 0.5 kg H2O kg−1). On an equal‐mass basis, net N mineralization and NH3 volatilization were larger in the fine fraction than in the whole litter, whereas respiration was similar in both materials. All processes increased with an increase in water content. These results suggest that the fine fraction should be managed similarly to the whole litter when applied to soil and that it may lose more NH3 than does the whole litter during storage, particularly at relatively high water contents.

N-Show: An Educational Computer Program that Displays Dynamic Graphs of Nitrogen in Soil

A careful study of the output of simulation models can help students understand concepts of crop production and soil management. Very often, graphical representation of the simulated data allows faster and easier understanding of the different processes occurring in a particular system. N-Show is an educational computer program that produces a dynamic, graphical representation of results generated by CERES--Maize, a simulation,model of corn (Zea mays L.) growth and development. The program allows the user to observe and compare the results of several runs of CERES--Maize, which were selected to demonstrate the effect of soil type and N rate on nitrate leaching. N-Show displays dynamic graphs of water and inorganic N contents in the soil, N in the plant, and N leached out of the soil profile. The unique feature of N-Show is that it allows the user to move the graphical display back and forth in time, thereby allowing careful study of the events that occur at specific times. N-Show could be used in undergraduate crop and soil courses and in training sessions for extension workers and farmers. CROP be useful tools for SIMULATION MODELS can teaching concepts related to crop production and soil management (Holt et al., 1976; Waldren, 1982; Meisner et al., 1991). Studying changes in specific variables (i.e., soil inorganic N, crop N uptake, etc.) with time can help students understand the underlying processes in a particular system. Very often, graphical representation of the data allows faster and easier understanding of existing relationships between variables. Two of the possibilities for graphically representing changes in several variables with time are: (i) to display the instantaneous value of each variable (for example in a vertical bar graph with a bar for each variable) and continuously update those values as time proceeds, and (ii) to display the value of each variable in the y axis and time in the x axis (a separate line for each variable). The fist option has the advantage of allowing the display of more variables, because no space is used for displaying the time dimension. Thus, the first option is attractive when the display space is limited, as is the case with typical computer monitors. Models that continuously update the display of variables usually provide a dynamic graph that changes as time moves forward (i.e., SWIM model from Ross, 1990; Scientific Software Group, 1993), but do not allow users to move the display forward and backward in time at their own will. In many cases, it would be convenient to move the display back and forth in time so that relationships between different variables can be better analyzed and Dep. of Crop and Soil Sciences/Institute of Ecology, Plant Sciences Bldg. 3401, Univ. of Georgia, Athens, GA 30602. Received 8 July 1993. *Corresponding author (mcabrera@uga.cc.uga.edu). Published in J. Nat. Resour. Life Sci. Educ. 23:43-45 0994). understood. N-Show is a computer program that provides students with that capability when analyzing simulated results related to the fate of N in soils. The program generates a dynamic, graphical representation of simulated results obtained with the CERES--Maize model (Jones-and Kiniry, 1986). MATERIALS AND METHODS Because the main objective of developing N-Show was to help students understand aspects of N cycling in a cropping systems, I chose the CERES--Maize model to generate the simulated results to be displayed. Soil files were prepared for two soils, a Cecil loamy sand (clayey, kaolinitic, thermic Typic Kanhapludults), representative of the Georgia Piedmont region, and a Tifton sandy loam (fineloamy, siliceous, thermic Plinthic Kandiudults), representative of the Georgia Coastal Plain region. Soil properties for 1.8-m profiles were provided in 10-cm increments for the upper 30 cm, and in 30-cm increments for the rest of the profile (Table 1). For each soil, simulation runs were made with N rates of 100, 200, and 300 kg N ha -l. The N applications were split in three equal amounts applied at planting, and at 41 and 62 d after planting. CERES--Maize version 2.1 was modified slightly to save (in one of the output files) some data that are normally generated by the model but are not saved to file. The modified output file provided values of soil nitrate concentrations in each layer, plant-extractable water content, total N uptake by corn, and total N leached below 1.8 m. These values, recorded every 7 d, are used by N-Show to provide a dynamic representation of the data.

Early Sweetpotato Plant Production Increased by GA3 and BA Plus GA4+7

Table 1. Influence of immersion in GA3 or BA + GA4+7 on cumulative number of early z plants harvested Treatments that decrease the interval from bedding to plant harvest or increase the number of sweetpotato [Ipomoea batatas (L.) Lam.] plants produced from bedded roots help reduce propagation cost and facilitate early transplanting. Immersing roots in 250 to 1000 mg/ liter gibberellic acid (GA3) before bedding increased the number of early and total plants produced (Tompkins and Bowers, 1970; Tompkins et al., 1973). However, those plants had thin, tough, wiry stems that could not be satisfactorily. transplanted mechanically (Tompkins et al., 1973). The cytokinin benzyladenine (BA) has been reported to interact with the activity of GA3 (Malik and Archbold, 1992) and GA,.,, the latter in a proprietary material (Miller, 1988). The objective of this study was to determine if using lower GA concentrations than previously reported would increase plant production without the plant distortion reported by Tompkins et al. (1973). ‘Georgia Jet’ and ‘Jewel’ roots were removed from storage on 13 Apr. 1990 and sorted for uniformly large canner size (2.5 to 5 cm in diameter, 5 to 18 cm long). Roots of each cultivar were assigned randomly to lots of 20 and immersed 10 min in solutions of GA3 at 0.5 or 1 mg·liter-1 (Pro Gibb 4%; Abbott Lab., North Chicago, Ill.), in solutions of BA + GA4+7 at 5 or 50 mg·liter -1(Promalin; Abbott Lab.), or not immersed (nontreated control). Roots were air-dried, placed in 40 × 60-cm contiguous plots in a greenhouse, and drenched with a fungicide solution prepared with 16 g of 75% wettable powder 2,6-dichloro-4-nitroaniline (dicloran)/liter. Roots were covered with 5 cm of fumigated Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudults). The propagating bed was watered immediately after bedding and thereafter as needed to ensure adequate moisture levels for plant production. After the first plant harvest, granular fertilizer [28.0N–12.3P–23.2K

Seasonal Phosphorus Losses in Runoff from a Coastal Plain Soil

Nutrients from agricultural fields can contaminate runoff and groundwater and enhance eutrophication. Runoff, soil loss, soluble P (SP), and bioavailable P (BP) associated with runoff and soil loss were measured from six 2 h simulated rainfall events (1 in./h) to determine amount of P transported during a corn (Zea mays L.) growing season and to develop relationships that predict P amounts and forms leaving different size field plots. Two 60-sq-ft microplots and two 6500-sq-ft mesoplots (3% slope) were located on a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult). Phosphorus was broadcast at 31 Ib P/acre, then incorporated to a depth of 6 in. Corn (conventional tillage) was planted after fertilizer application. Six simulated rainfall events occurred 5 d before and 1, 14, 29, 49, and 108 d after fertilizer application [...]

Root Hair Occurrence anld Variation with Environment

AbstractEarly literature on peanut [Arachis hypogcrea (L.)] indicates the existence of two forms of root hairs: (i) a rosette form of root hair (4 mm long) occurring; radially where a lateral root initiates from a primary root, and (ii) shorter (0.30 mm), more profuse root hairs occurring along root lengths usually behind the root tip. Since little is known about the factors that influence peanut root hair formation, the purpose of this study was to quantify root hair formation under various soils and water stress conditions. Separate rhizotron, field, and greenhouse studies were conducted. The rhizotron study showed no differences in the percentage of roots having root hairs regardless of water stress treatments imposed 20 to 50 and 50 to 80 days after planting (DAP). Thirty‐seven to 43% of the roots had root hairs. In the field, peanut root systems growing within dialysis root bags in a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudults) showed a significant increase in root hair formation from 7% at 70 DAP to 31% at harvest. In the greenhouse using three soil types, Greenville fine sandy loam (clayey, kaolinitic, thermic Rhodic Kandiudults), Tifton loamy sand, and a 4:1 coarse sand:fritted clay mixture (rhizotron), soil type was found to affect the percentage of roots having root hairs. Roots growing in the Tifton, sand:fritted clay mixture, and Greenville soils had 47, 17, and 14% root hairs, respectively. In all studies, the rosette form of root hair around lateral initiates was observed. Approximately 66% of the lateral initiates expressed rosette‐type root hairs. Mycorrhizal infection, though insufficient to significantly affect nutrient uptake, was greater with the rhizotron (18%) than the Greenville (6%) and Tifton soils (3%). There may be a possible interaction between root hair occurrence and mycorrhizae infection.