Thermic Typic Hapludult Research Articles

Growth of Relay Intercropped Soybean

AbstractRelay intercropping of wheat (Triticum aestivum L.) and soybean [Glycine max (L.) Merr.] allows for earlier soybean planting than in conventional doublecropping systems, but shading and other influences of the wheat crop may be detrimental to intercropped soybean development. The purpose of this study was to determine the effect of relay intercropping on soybean growth and yield. Intercropped soybean, planted 19 (1989) or 14 (1990) days before wheat harvest, was compared with a control treatment (same no‐till planting pattern and date, but no wheat) on a Cecil sandy loam (clayey, kaolinic, thermic Typic Hapludults) soil. Intercropping had a greater influence on soybean growth in 1989, when there was more shading by the wheat canopy and also when the period between soybean planting and wheat harvest was longer, than in 1990. In both years, the greatest effects of intercropping on growth occurred early in the season, when intercropped plants were taller but had smaller stem diameters, less leaf area, and less aboveground dry weight, as compared with control plants. Photosynthetic rates of upper canopy leaves were reduced by intercropping for 2 wk after wheat harvest in 1990. This was associated with an increase in specific leaf area in intercropped plants. Lateseason growth, including that of reproductive parts, was similar for intercropped and control treatments, and there were no detectable effects of intercropping on final yield components or yield in either year. In environments where the period of overlap between the wheat and soybean crops is relatively short, negative effects of relay intercropping on early soybean growth may not result in yield reductions.

Soil Loss and Silage Yield for Three Tillage Management Systems

Corn (Zea mays L.) for silage is commonly grown in the southeastern USA in fields with rolling topography where rows often run up and down slope, promoting surface water runoff and soil erosion. The objective of this study was to assess one conventional and two nonconventional tillage-management systems on silage yield, water runoff, and soil loss on sloping fields in the Piedmont of the southern USA. The study was conducted on an Appling sandy loam (clayey, kaolinitic, thermic Typic Hapludults) on a 4% slope with 12% clay and 66% sand in the Ap horizon (...)

Nitrogen Outputs from a Field‐Size Agricultural Watershed

AbstractNitrogen outputs from a 0.34‐ha field were measured for 1984 through 1987. The field consisted of Cowarts loamy sand (fine‐loamy, siliceous, thermic Typic Hapludult) managed in a summer row crop‐winter cover crop sequence. Outputs measured were subsurface flow, surface runoff, and denitrification. Monthly sampling of denitrification rates showed a high degree of temporal and spatial variability. Rates significantly increased with soil moisture and depth. Denitrification also increased after irrigation events. Nitrogen movement in subsurface flow was 97% NO3‐N and was about 10 times that in surface runoff. Most subsurface flow and movement of N (77 kg NO3‐N ha−1) occurred in December 1986 through February 1987 when 62 cm of precipitation fell in a 12‐wk period (December 1986–February 1987) following fertilizer application. This period accounted for one‐half the total subsurface nitrate movement for the 4‐yr study. Even though no crop was harvested in 1985, subsurface outputs of N were low in winter of 1985–1986. Soil NH4‐N levels were significantly higher after the year without a harvest, indicating that more of the N in crop residue was found in the soil pool.

Crop and Tillage Rotations: Grain Yield, Residue Cover, and Soil Water

AbstractInformation regarding crop yield response for different tillage and rotation systems is needed to determine regional or local suitability for a given production system. Our objective was to determine the effects of continuous and alternating tillage sequences in corn (Zea mays L.) monoculture and corn‐soybean [Glycine max (L.) Merr.] rotation on residue cover, soil water, and grain yield. Continuous conventional tillage (CT), continuous no‐tillage (NT), or CT and NT alternating every other year were evaluated during a 5‐yr period on a Rion (fine‐loamy, mixed, thermic Typic Hapludult)‐Pacolet (clayey, kaolinitic, thermic Typic Kanhapludult) sandy clay loam complex at a Piedmont location and an Eunola sandy loam (fine‐loamy, siliceous, thermic Aquic Hapludult) at a Coastal Plain location. The 5‐yr average NT corn grain yield was 27% (1.15 Mg ha−1) higher than CT at the Piedmont location, but only 4% (0.32 Mg ha−1) higher at the Coastal Plain location. Continuous NT at the Piedmont location also resulted in higher corn yields 2 out of 4 yr compared with NT following CT. The increase in corn yield with NT was associated with greater soil water availability, primarily attributed to surface residue cover from corn stover fostering greater infiltration on a crust‐prone soil. Soybean yield during the 5‐yr period was 5% higher with NT at the Piedmont location and unaffected by tillage at the Coastal Plain location. In general, crop rotation had no effect on corn yield at either location. Results indicate that continuous NT should be the system of choice on this upland Piedmont soil.

Determining differential water movement through ion exchange resin for nitrate leaching measurements

Abstract The fate of fertilizer N applied to agricultural soils is of growing concern due to the potential for groundwater contamination. The recent development of an exchange resin that specifically absorbs NO3 has led to the potential for a new technique to measure cumulative NO3 leaching. The main limitation to the application of the resin technique is the matching of water movement through the resin with that of soil. A soil water movement device was developed to compare water movement through the resin to that of soil. A study was initiated to develop a resin/soil pack with water movement characteristics that closely matches those of natural soils. Three different soil types were used in this study: a Cahaba sandy loam (fine‐loamy, siliceous, thermic Typic Hapludult), a Congaree clay loam (fine loamy, mixed, nonacid, thermic Typic Udifluvent), and a Hiwassee clay (clayey, kaolinitic, thermic Typic Rhodudult). Both pure resin and resin mixed with soil were found to have higher water movement characteristics compared to bulk soil. A resin pack method was found which had water movement characteristics that were not significantly different from that of bulk soil for the three different soil types. The resin pack method is described.

Ammonia volatilization from urea, ammonium sulfate and NutraSweet sludge in bare and straw‐covered soils

Abstract NutraSweet sludge, a by‐product from the manufacture of the artificial sweetner aspartame, is often applied to land as fertilizer. In many cases, the sludge is surface‐applied, which could result in gaseous losses of nitrogen. In order to determine the relative importance of nitrogen losses through ammonia volatilization, a laboratory study was conducted to compare NutraSweet sludge with ammonium sulfate and urea at equivalent rates of nitrogen. The materials were surface‐applied to two soils in the presence or absence of a surface mulch of straw, and ammonia volatilization was measured over a 16‐day period at 25°C. The soils were collected from areas mapped as Tifton (Fine loamy, siliceous, thermic Plinthic Paleudults) and Dothan (Fine loamy, siliceious, thermic Typic Hapludults) series, respectively. The results show that relative to urea, the NutraSweet sludge loses ammonia more slowly throughout the incubation period but particularly in the initial stages. The straw did not affect ammonia vol...

Interaction of tillage and soil type on available water in a corn-wheat-soybean rotation

Drought stress often reduces grain yield of warm-season crops in the southern Piedmont and South Atlantic Coastal Plain. No-till systems may reduce drought stress by reducing losses of water from runoff and surface evaporation. The objective of this study was to determine the effect of no-till (NT), either continuous or in alternating sequences with conventional tillage (CT), on soil water content during the warm season in a corn ( Zea mays L.)-wheat ( Triticum aestivum L.)-double-crop soybean ( Glycine max. L. Merr.) rotation. A field study was conducted for 3 years on an Aycock fine sandy loam (fine-silty, siliceous, thermic Typic Paleudult) in the Coastal Plain region and for 2 years on a Pacolet sandy clay loam (clayey, kaolinitic, thermic Typic Hapludult) in the Piedmont region. Soil water content was measured to a depth of 0.9 m in corn and soybean in the following four tillage sequences: (1) continuous NT; (2) NT corn-CT wheat-NT soybean; (3) CT corn-CT-wheat-NT soybean; (4) continuous CT. For the Pacolet soil, soil water content was frequently higher in NT than in CT, particularly in the Ap horizon under corn. Differences in water content in the Ap ranged from 0.030 to 0.100 m 3 m −3. Differences in water content occurred infrequently on the Aycock soil, and were of smaller magnitude. Tillage of the previous crop had no effect on soil water content. Results indicate a high potential for NT systems to reduce drought stress on upland soils in the Piedmont subject to surface sealing and runoff. The potential is less for nearly level soils of the Coastal Plain.

Establishment of Two Bermudagrasses in Three Soil Environments

AbstractTifton 44 hybrid bermudagrass [Cynodon dactylon (L.) Pers.], has been reported to be more cold tolerant and to give better animal gains than the hybrid Coastal. It has been observed that Tifton 44 has not established as rapidly as Coastal, frequently taking 2 to 3 yr to achieve complete ground cover. The objective of this work was to determine and quantify differences in the field establishment of Coastal and Tifton 44 grown at three locations for 2 yr on clayey, kaolinitic, thermic Typic Hapludult (Cecil and Mayodan) and loamy, siliceous, thermic Grossarenic (Blanton) soils in North Carolina. A single row of sprigs was set in the center and the length of each 3.1‐ by 6.2‐m plot. Establishment effects were measured by weekly counts of the number of tillers/stolons intercepting a series of transect lines spaced at 0.15‐m intervals on both sides of the sprigged row, and by harvesting the forage produced at the end of the season in 0.30‐ by 6.1‐m increments from the center to the border of each plot. Two establishment indices were developed as the response variables from the transect count data. Analyses of variance were conducted on yield, establishment indices, and on spring ground cover estimates. Yield of forage and establishment characteristics were similar for Coastal and Tifton 44 on the Mayodan soil, but Coastal established more rapidly and produced more forage than Tifton 44 on the Cecil soil in both years of the trial and on the Blanton soil during the first year. In three of six trials, Tifton 44 would have required a 0.3‐ to 0.6‐m row spacing to equal the coverage obtained by Coastal in a 0.9‐ to 1.2‐m row spacing.

Soil Ca, Al, acidity and penetration resistance with subsoiling, lime and gypsum treatments

Abstract. Crop growth on strongly weathered soils is often limited by soil compaction in addition to aluminium toxicity and/or calcium deficiency. This study examines the effects of subsoiling, lime and gypsum on penetrometer resistance, acidity, aluminium and calcium levels and cotton (Gossypium hirsutum L.) root growth on soils transitional between Cecil and Appling series (clayey, kaolinitic, thermic Typic Hapludults) in the Piedmont region of Georgia, USA. The main plots were subsoiled to depths of 0.35 or 0.80 m or untreated. Dolomitic limestone (0 or 4.03 t per hectare on subplots) and phosphogypsum (0 or 10 t per hectare on sub‐subplots) were incorporated into the surface soil (0.15 m). Deep subsoiling (0.80 m depth) decreased penetrometer resistance at 0.3–0.5 m depth and increased yield in two of three years, but there was no response to shallow subsoiling (0.35 m depth). Lime increased yield when surface soil water pH prior to amendment was less than a Cate‐Nelson critical value of 4.6. Gypsum moved downward much more rapidly than lime, increasing soil solution calcium ion activity to a depth of 0.8 m within 5 months of application. There were differences in clay content between replicate plots and calcium movement was faster where the clay content was less. Yield responses to gypsum in 1986 were attributed to increased root growth below 0.2 m resulting from the increased calcium ion activity. Yield response to gypsum in limed sub‐subplots was significant only in 1986.

Potassium fertilization effects on yield and longevity of established alfalfa

Abstract Limited information is available which describes the response of established alfalfa (Medicago sativa L.) to topdressing applications of K fertilizer in the Southeastern United States. Field experiments were conducted for three years to determine alfalfa response to rates and time of K application. The experiments were established in two‐year old stands of alfalfa on a Decatur silty clay loam (clayey, kaolinitic, thermic Rhodic Paleudults) and a Hartsells fine sandy loam (fine loamy, siliceous, thermic Typic Hapludults) located in northern Alabama. Potassium as KCl was broadcast in the spring prior to regrowth. For split application treatments, the K was applied in early spring and after the second cutting. Annual total K rates ranged from 56 to 596 kg/ha. Potassium fertilization maintained alfalfa stand density on both soils, but the experiment on the Decatur soil was discontinued after two years due to severe stand loss when the lowest rate of added K was used. Alfalfa yields were increased by ...

Calcination Effect on the Agronomic Effectiveness of Apatitic North Carolina Phosphate Rock

AbstractCalcination of apatitic phosphate rock (PR) is one of the means to increase the grade (total P content) of the mineral. The objective of this study was to investigate the effect of calcination on the solubility and agronomic effectiveness of apatitic North Carolina PR in a greenhouse experiment. A Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult) with pH 4.8 was used. Fertilizers were mixed with the soil at P rates of 0, 50, 150, and 300 mg P kg−1. Funks G5757 maize (Zea mays L.) was grown for 6 wk for each of two crops. The results showed that the degree of carbonate substitution for phosphate in the apatite structure was decreased from 1.20 to 0.32 mol after calcination. The corresponding decrease in neutral ammonium citrate solubility was from 2.7 to 0.8%. Dry‐matter yield and P uptake by maize in two successive crops also decreased due to calcination. Across the range of the P rates used in two maize crops, an average reduction in dry‐matter yield of 77% was calculated for the calcined PR relative to uncalcined PR. Thus, apatitic PR used for direct application should not be calcined, even though calcination can increase its total P content.

Potassium Fertilization of Doublecropped Wheat and Soybeans under Two Tillage Systems

Because the yield response to K in a wheat (Triticum aestivum L.)-soybean [Glycine max (L.) Merr.] rotation on Atlantic Coastal Plain soils may be influenced by tillage type and K application timing, a study was conducted between 1986 and 1988 on a Bojac loamy sand (coarse-loamy, mixed, thermic Typic Hapludult) to investigate the effects of tillage, K rate, and K application timing on soil and plant K and crop yields. The experimental design was a split plot, with tillage as the main plot factor and K rate × K application timing as the subplot factor. Tillage treatments were conventional tillage (CT) and no-till (NT). Potassium fertilizer (KC1) rates of 0, 36, and 72 lb K/acre were applied (i) 100% prior to wheat planting; (ii) 50% prior to wheat planting, 50% at Zadoks 30 growth stage; and (iii) 50% prior to wheat planting, 50% prior to soybean planting. Wheat yields under continuous NT management declined from 84 bu/acre in 1987 to 53 bu/acre in 1988, while CT wheat yields remained constant at 76 bu/acre in 1987 and 75 bu/acre in 1988. No-till soybeans significantly outyielded CT soybeans by 48 to 33 bu/acre in 1987 and 61 to 46 bu/acre in 1988. Neither wheat nor soybeans responded to K rate or timing of application despite reductions in soil test K to levels diagnosed as insufficient. Leaching losses contributed significantly to declines in soil K, as crop removal accounted for only a portion of the “missing” K. Testing for K on Coastal Plain soils should involve subsoil sampling, since both wheat and soybeans appear capable of procuring considerable amounts of K from deeper than 12 to 18 in. within the profile.

Predicting Cation Mobility in Kaolinitic Media Based on Exchange Selectivities of Kaolinite

AbstractPredictive modeling of cation transport in soils requires knowledge of the distribution of exchangeable species between solution and adsorbed phases. Such distribution of exchangeable species may be described with an exchange selectivity coefficient. Typically, the selectivity coefficient for any cation‐exchange pair varies among soils. If the exchange complex of a soil is dominated by one type of exchanger, however, then the selectivity coefficient for that soil may be similar in magnitude to that for the principal mineral (or organic) constituent. Therefore, reasonably accurate predictions of cation transport in that soil might be obtained using exchange data for the dominant exchange material. This study was undertaken to determine whether exchange data for kaolinite could be successfully used in predicting Ca, Mg, and Na retention during movement in a Mahan series soil (clayey, kaolinitic, thermic Typic Hapludult). Binary‐exchange isotherms for Ca‐Mg, Ca‐Na, and Mg‐Na were generated for Ga‐1 kaolinite (well crystallized). Selectivity coefficients derived from these data were used to describe cation exchange during miscible displacement through columns of (i) kaolinite admixed with acid‐washed sand and (ii) Mahan soil. Use of the selectivity coefficients for kaolinite provided good predictions of cation transport in the kaolinite/sand mixture. Predictions for the kaolinitic Mahan soil were not as good. The presence of small amounts of 2:1 minerals may have influenced the overall exchange behavior of the Mahan soil. When the uncertainty in values for selectivity coefficients and other exchange or transport parameters was considered, however, the exchange selectivity data for kaolinite could adequately describe cation transport in the Mahan soil.

Phosphate Rocks Compacted with Superphosphates vs. Partially Acidulated Rocks for Bean and Rice

AbstractPhosphate rocks (PR), which have low reactivity and contain large amounts of Fe and Al oxides, may be both ineffective as direct‐application fertilizers and unsuitable for partial acidulation. Such PRs can be made more effective by mixing them with soluble phosphates and compressing the mixture into pellets. The agronomic effectiveness of such pelletized mixtures was compared with that of partially acidulated phosphate rocks (PAPR), in pot trials with upland rice (Oryza sativa L.) and kidney bean (Phaseolus vulgaris L.) as indicator crops. Capinota PR, (CPR) which is low in reactivity and contains 8.8% Fe2O3 + Al2O3, and moderately reactive Huila PR (HPR), with 2.3% Fe2O3 + Al2O3, were mixed with triple superphosphate (TSP) to provide 50% of the total P in water‐soluble form in the mixture. The mixtures were then compacted into pellets. A Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult, pH 4.5) was used in the study. With TSP as the standard (assuming 100% effectiveness), pelletizing it with CPR increased the CPR's relative effectiveness from 43% before treatment to 80% after for rice grain production and from 51% before treatment to 92% after for bean biomass yield. Likewise, P uptake by rice increased from 47 to 79% and uptake by beans from 51% to 92% of that of TSP for CPR compacted with TSP. The moderately reactive HPR, low in Fe2O3 + Al2O3, the Huila PAPR (HPAPR), and the compacted HPR pus TSP were 83 to 86% as effective as TSP in increasing grain yield of rice and 75 to 81% as effective in promoting P uptake. For bean, the relative effectiveness of HPR, HPAPR, and compacted HPR plus TSP was 88 to 95% for biomass yield and 80 to 88% for P uptake. This study confirms that, for some PRs that have low reactivity and high Fe2O3 + Al2O3 contents, compaction with soluble P fertilizers is agronomically more effective than partial acidulation.

No-Till Corn Response to Nitrogen Rate and Timing in the Middle Atlantic Coastal Plain

Improved N use efficiency for no-till corn (Zea mays L.) production on sandy soils may be enhanced with split applications of N fertilizer immediately prior to periods of highest N uptake. A field study was conducted in 1988 and 1989 at the Eastern Shore Agricultural Experiment Station in Painter, VA, on a Bojac loamy sand (coarse-loamy, mixed, thermic Typic Hapludult) to investigate split N applications near silking. Nitrogen treatments (as 30% N-urea ammonium nitrate solution) of 0, 36, 72, 108, and 144 lb N/acre at the 5-leaf growth stage (ENR) were factorially arranged with 0, 25, 50, 75, and 100 lb N/acre applied at the 16-leaf stage (LNR) in a randomized complete block design with three replications. Corn cultivar Pioneer Brand 3320 was planted no-till into a killed winter rye (Secale cereale L.) cover crop onto the same site each spring. At the 14-leaf stage, samples of the leaf immediately below the whorl were collected from each plot and analyzed for N, P, K, Ca and Mg. Yield response was attributed less to timing of N applications than to the total N rate; however, at least 36 lb N/acre were required at the 5-leaf stage to prevent N deprivation and reduction of yield potential. While LNR treatments increased yield at all ENR treatments, the greatest yield response to late N application was obtained between 36 and 72 lb N/acre applied early. At equal N rates, N use efficiency was not significantly affected when fertilizer N applications were split between the 5-leaf and 16-leaf growth stages. Under the high rainfall conditions which increased yield and nitrate leaching potentials, recommended 16-leaf stage N rates for 14-leaf N concentrations of 1.7 to 2.0% ranged from 85 to 92 lb/acre. Calibration of 16-leaf stage fertilizer N requirements with 14-leaf stage critical N values were not successfully developed for leaf N concentrations greater than 2% because yields were not maximized despite total N applications considerably higher than routinely recommended. Diagnosis and Recommendation Integrated System (DRIS) norms developed in Georgia did not accurately diagnose corn N status in Virginia; hence, local calibration of DRIS norms is necessary.

Yield and elemental composition of wheat grain as influenced by source and rate of nitrogen

Abstract Application of sewage sludges to winter wheat (Triticum aestivum L.) is a possible mechanism to supply nutrients to the crop while simultaneously reducing the need for more expensive and less desirable disposal strategies. Research was conducted during 1986 and 1987 to determine the effect of fall applied sewage sludges on yield, N recovery, and elemental composition of wheat grain. The study was conducted in a corn (Zea mays L.)‐wheat‐soybean [Glycine max (L.) Merr.] rotation located on a Suffolk sandy loam soil (coarse, loamy, siliceous, thermic Typic Hapludult). The N treatments applied consisted of 0 (control), 30, 60, and 90 kg N ha‐1 from UAN solution applied in the spring and two anaerobically digested sewage sludges (one lime conditioned and the other lime stabilized) designed to supply 80 kg of plant available N ha‐1 applied in the fall. Twenty kg of N as UAN solution were applied in the fall when the wheat was seeded to all treatments except the control and the sewage sludge treatments....

Comparative availability to wheat of metals from sewage sludge and inorganic salts

A greenhouse experiment was conducted to evaluate the availability of metals from sewage sludge and inorganic salts, and the effect of pH and soil type on yield and metal (Zn, Cu, Cd and Ni) uptake by wheat (Triticum aestivum L. var. ‘holly’). Soils used in this study were Hartsells sandy loam (fine-loamy, siliceous Thermic Typic Hapludult) and Decatur silty clay loam (Clayey, kaolinitic, Thermic Rhodic Paleudult). Two treatments of sewage sludge containing metals were applied at the rate of 20 and 100 mt ha−1. Inorganic Salts of Zn, Cu, Cd, and Ni were applied (as sulfate salts) at concentrations equivalent to those found in the 20 and 100 mt ha−1 sludge. One treatment consisted of inorganic metals plus sewage at the 20 Mg ha−1 rate. Two soil pH levels, one at field pH (below 6.0) and another pH adjusted between 6.5 and 7.0 were used. Wheat plants were harvested four weeks after germination. Two more subsequent harvests were made at four week intervals. For each harvest, dry matter yield increased as the rate of sludge application increased for both soil types. The soil pH also influenced the dry matter yield. High yield was observed when the pH was adjusted between 6.5 to 7.0 for both soils. An increase in yield was also observed at each subsequent harvest for most of the treatments. Inorganic salt treatments produced lower dry matter yields when compared with the sludge. Both sludge application and metal salts increased plant tissue concentration of Zn, Cu, Cd, and Ni at field pH for both soils. However, increasing the pH of the soil for both sludge and inorganic salt treatments generally decreased the tissue concentration of the above metals.

Anionic Effects on Potassium Reactions in Variable-Charge Atlantic Coastal Plain Soils

To better understand the role anions play in the rate of cation adsorption, the effect of anions on K mobility, retention, and rate of K reactions in two variable-charge Atlantic Coastal Plain soils was investigated. The soils studied were a Rumford loamy sand (coarseloamy, siliceous, thermic Typic Hapludult) and a Kenansville loamy sand (loamy, siliceous, thermic Arenic Hapludult). The effects of ClO4, Cl, SO4, PO4, and SiO3 on the rate and magnitude of K adsorption on the two soils was investigated at pH 5 and 6 using a stirred-flow kinetic technique. The type of anion present had little, if any, effect on the rate of K adsorption, but had an effect on the amount of K adsorbed. In general, the amount of K adsorbed in the presence of a particular accompanying anion was of the order SiO3 > PO4 > SO4 > Cl > ClO4. When SiO3 was the accompanying anion in a 20 mg K L−1 solution, K adsorption on the Rumford soil was as high as 358 mg K kg−1, vs. a K adsorption maximum of only 58 mg K kg−1 when ClO4 was the accompanying anion. Likewise for the Kenansville soil, the SiO3 maximum was 321 mg K kg−1 while the ClO4 maximum was only 89 mg K kg−1. These studies demonstrate the role anions play in K retention and mobility, specifically on variable-charge Atlantic Coastal Plain soils.

Seasonal Performance of Several Clovers Grown as Annuals in Southern Alabama

(...) Seven clovers were evaluated at four locations in southern Alabama to determine seasonal yield distribution and dependability. Soils were Malbis fine sandy loam (fine-loamy, siliceous, thermic Plinthic Palendult), Lucedale sandy clay loam (fine-silty, carbonatic, thermic Rendollic Eutrochrept), Sumter clay (fine-silty, carbonatic, thermic Rendollic Eutrochrept), and Cahaba fine sandy loam (fine-loamy, siliceous, thermic Typic Hapludult). The experimental design was a randomized complete block with four replications at each location. Experiments were seeded in autumn at each location each year from 1985 through 1987 (...)

Soil Variables and Interactions Affecting Prediction of Crop Yield Pattern

The pattern and magnitude of crop yield variability in a field reflect soil conditions that influence yield to varying degrees during critical portions of the crop season. Variables accounting for the majority of soybean [Glycine max (L.) Merr.] yield variation, measured on 40 farm fields on either Cecil or Pacolet soil (clayey, kaolinitic, thermic Typic Hapludults) landscapes during 1982 and 1983, were previously identified by using factor analyses and components regression. The objective of this study was to determine the nature of interactions among clay at 0 to 0.1 m, C at 0 to 0.1 m, rainfall (Day 214 to 280), pH at 0 to 0.1 m and 0.45 to 0.55 m, and integrated soil water tension at 0.1 and 0.5 m. Analyses were done in relation to soybean grain yield using two-point and four-point, two-dimensional sliding polynomials. As clay content at 0 to 0.1 m increased from 3 to about 18%, crop yield was greatly decreased, modulus of rupture was increased, and the yield response to pH, rainfall, and soil water tension was reduced. Soybean yield on soils with clay contents greater than 20% at 0 to 0.1 m was significantly modified by soil C content. At 39.2% clay, crop yield was affected very little by soil water tension at 0.1 m, by rainfall, or by pH at 0 to 0.1 m. More than 255 mm of rainfall between Day 214 and 280 increased yield only on sites with high C levels, e.g., 11.93 g kg−1. In spite of significant variate interactions, linear and noninteractive 5 and 10-term component regression models demonstrated good potential for predicting soybean grain yield.