Gary W. Hergert

Fractal analysis of spatial and temporal variability

Abstract Characterizing spatial and temporal variability is important in variable rate (VRAT) or long-term studies. This study was conducted to compare spatial variability of soil nitrate in a VRAT nitrogen (N) application study and temporal variability of soybean (Glycine max L.) yield in a long-term organic vs. inorganic study. In the VRAT study, conventional uniform N application was compared with variable rate and variable rate minus 15% N. In the long-term experiment, soybean yields under organic (manure application), fertilizer, and fertilizer plus herbicide systems were studied from 1975 to 1991. Semivariograms were estimated for soil nitrate in the VRAT and for soybean yield in the long-term study. The slope of the regression line of log semivariogram vs. log lag (h, distance or year) was used to estimate the fractal dimension (D), which is an indication of variability pattern. The intercepts (log k) of the log–log lines, which indicate extent of variability, were also compared between treatments. There was no significant effect of the N treatments on the D-values in the VRAT study. The extent of spatial variability for residual soil nitrate became significantly less after imposing N application regimes. The variable rate N application had lower log k-values than uniform application indicating reduced soil nitrate variability with VRAT N application. In the long-term study, all three management systems had similar D and log k-values for soybean yield indicating similar temporal yield variability for the three systems. The three management systems used did not change temporal effects on soybean yield. Rainfall during July and August accounted for 65% of variability in soybean grain yield. Fractal and covariance analyses can be effectively used to compare treatments or management systems for spatial or temporal variability.

Fertilizer and crop management practices for improving maize yields on high pH soils

Abstract In Nebraska, nearly 0.4 million hectares (ha) of maize (Zea mays L.) are subjected to varying degrees of iron (Fe) chlorosis from high pH soil. A factorial design with two maize varieties (tolerant and non‐tolerant) and seed row applied Fe treatments with four replications was used on three soil areas of Cozad silt loam with pHs of 8.6, 8.2, and 7.7. Iron treatments included a check, seed row applied FeSO4•7H2O, FeEDDHA, dried granular FeSO4‐polyacrylamide gel and foliar sprays of 1.5% FeSO4•7H2O. Chlorophyll meter readings at V8 and V10 separated treatment effects on the pH 8.6 site and were highly correlated with yield. In 1993, all Fe treatments on the pH 8.6 site produced significant yield increases on both varieties except the foliar treatment and FeEDDHA on the non‐tolerant hybrid. The FeSO4‐polyacrylamide gel was especially effective, but was not available in 1994. Most Fe treatments significantly increased yields on the pH 8.2 and 8.6 sites, but not the pH 7.7 site. In 1994, most Fe treat...

Skip-Row Planting Patterns Stabilize Corn Grain Yields in the Central Great Plains

The highly variable climate of the central Great Plains makes dryland corn (Zea mays) production a risky enterprise. Twenty-three field trials were conducted across the central Great Plains from 2004 through 2006 to quantify the effect of various skip-row planting patterns and plant populations on grain yield in dryland corn production. A significant planting pattern by plant population interaction was observed at only one of 23 trials, suggesting that planting pattern recommendations can be made largely irrespective of plant population. In trials where skip-row planting patterns resulted in increased grain yields compared to the standard planting pattern treatment (every row planted using a 30-inch row spacing), the mean grain yield for the standard planting treatment was 44 bu/acre. In those trials where skip-row planting resulted in decreased grain yield compared to the standard planting pattern, the mean yield was 135 bu/acre. The plant two rows, skip two rows planting pattern is recommended for riskaverse growers in the central Great Plains where field history or predictions suggest likely grain yields of 75 bu/acre or less. Planting one row and skipping one row is recommended for growers with moderate risk-aversion and likely yield levels of 100 bu/acre or less.

A futuristic view of soil and plant analysis and nutrient recommendations

Abstract The wide scale adoption of site specific management (SSM) and variable rate fertilizer application (VRA) in the next 5 to 10 years portends changes in soil testing and plant analysis. To develop site specific nutrient recommendations, more detailed information about the soils fertility status will be required which could mean greatly increased samples numbers for soil or plant analysis. Discussions of initial research on the large numbers of samples required to produce quality maps for SSM and VRA among scientists, agricultural industry and producers, however, indicates that this may only be a short phase as the expectation of using remote sensing (RS) to replace or compliment limited soil and plant analysis is already occurring. Soil and plant analysis numbers may increase during the next 5 to 10 years as there is a slow transition to SSM and VRA. During this time, however, there will be research to related RS imagery to soil and crop management problems. After 10 years of this transition, ther...

Sugar Beet Fertilization

Global sugar beet production spans diverse regions and a wide range of climatic and agroecological regions from rainfed to irrigated production which presents unique management challenges. Sound nutrient management now and into the future must be balanced between production efficiency and managing to have less impact on the environment. N management continues to improve with more precise N rates. Soil testing for N supplying capability plus residual N will need to be increased to enhance productivity and N use efficiency. Newer cultivation techniques, N placement and timing can also fine tune N rates. In irrigated areas, improvements in N management will be coupled with better water management and conversion of furrow irrigation to sprinklers will accelerate improvements. Enhanced efficiency fertilizer products hold promise but require additional research under a range of conditions to determine cost and production effectiveness. Management for secondary and micronutrients seems adequate at this time. Precision agricultural applications for expanded site specific management in sugar beet are just beginning. Work with maize and wheat point to the potential of creating different management zones in fields and by using remote or close sensing to determine N status for N applications. Similar research will be needed to continue efficient sugar beet production.

Fly ash as a liming material for corn production

Fly ash produced as a by-product of subbituminous coal combustion can potentially serve as an alternative liming material without negatively affecting corn (Zea mays L.) production in areas where use of conventional liming materials can be uneconomical due to transportation costs. A study was conducted to determine if fly ash produced from the Nebraska Public Power District Gerald Gentleman Power Station located in Sutherland, NE could be used as an alternative liming material. This study had the following objectives: 1) compare the effects of fly ash on soil pH with other common agricultural lime materials; 2) determine the effects of fly ash on percent Al saturation in selected soils; and 3) determine the effects of fly ash on corn grain yields. Combinations of dry fly ash (DFA), wet fly ash (WFA), beet lime (by-product of sugar beet [Beta vulgaris L.] processing) (BL), and agricultural lime (AGL) were applied at rates ranging from 0.43 to 1.62 times the recommended lime rate to plots on four acidic soils (Anselmo fine sandy loam, Hord fine sandy loam, Holdrege sandy loam, and Valentine fine sand). Soil samples were collected to a depth of 0.2 m from plots and analyzed for pH before lime applications and twice periodically after lime application. The Hord and Valentine soils were analyzed for exchangeable Ca, Mg, K, Na, and Al for determination of percent Al saturation on selected treatments and sampling dates. Corn grain yields were determined annually. Depending on the lime source, soil pH increased in the upper 0.2 m of soil the year after application compared with the pre-application soil pH values for some sites and years, whereas in others there were no significant increases in pH. However, all lime materials at each site failed to raise the soil pH in the upper 0.2 m of all the treatments and soil types to the target pH of 6.5. Fly ash and AGL treatments did not significantly increase corn grain yields compared with the control on the Anselmo, Hord, and Holdrege soils. At the Hord site, AGL and DFA significantly reduced percent Al saturation by 3.1% and 3.7% compared with the control 5 years after application, respectively. Fly ash did not negatively affect corn grain yields compared with AGL. Yields were 12,472, 12,233, and 12,177 kg ha−1 for the Anselmo, Holdrege, and Hord sites averaged over all treatments and years. The lack of yield response to lime additions was potentially a result of lime materials not raising the soil pH to sufficient levels, higher subsoil pH values, or the exchangeable Al not being high enough prior to lime material application to reduce grain yields in these soils. We conclude that the fly ash utilized in this study and applied at rates in this study, increases soil pH comparable to agricultural lime and is an appropriate alternative liming material.

Irrigation Soybeans by Growth Stages in Nebraska

Irrigated soybean production in Nebraska spans a region with diverse soils and climates. Irrigators can easily adopt irrigation scheduling using a stage of growth for timing applications. However, simplifying assumptions, including soil water holding capacity, rainfall, stored soil water, and adequate irrigation system capacity, are implicit in the development of stage of growth irrigation scheduling recommendations. Reliance on these can lead to misapplication of irrigation water. This project tested irrigation scheduling techniques for indeterminate soybean production in Nebraska, with stage of growth indicating the initiation of irrigation. The range of soils and climate in the study area gave a range of irrigation scheduling recommendations. In the semi-arid, west-central Nebraska, full-season irrigation to meet evapotranspiration demand has been recommended. In sub-humid, south-central and eastern Nebraska, irrigation can be delayed until flowering on deep medium to fine textured soils if the potential root zone is filled at planting time.

Phytosiderophore release from nodal, primary, and complete root systems in maize

Some maize (Zea mays L.) hybrids grown in high pH soil in Nebraska suffer from severely reduced yields caused by iron (Fe) deficiency chlorosis. Hybrids which recover from early season Fe-deficiency chlorosis and yield well are termed Fe-efficient or tolerant. Most Fe-efficient gramineous species respond to Fe-deficiency stress by releasing phytosiderophores (mugineic acid and its derivatives) into the rhizosphere, thereby increasing Fe availability and uptake of the Fe3+-phytosiderophore complex via a high affinity uptake system. Field-grown Fe-efficient maize recovers from Fe-deficiency chlorosis at a stage when nodal roots have become the dominant root system. Quantifying phytosiderophore release from hydroponically grown plants has been proposed as a viable alternative to time-consuming and variable field trials and has been used successfully to delineate among Fe-efficient and Fe-inefficient lines of oat (Avena sativa L.) and wheat (Triticum aestivum L.). Our objectives were (1) to determine if phytosiderophore release differed between nodal- and primary-root systems of maize, and (2) to compare phytosiderophore release from 12 hybrids. Root exudates secreted during daily 4-h collections were analyzed for their Fe-solubilizing ability, which was equated to phytosiderophore release. Nodal root systems released significantly more phytosiderophore than primary- or complete-root systems. In early experiments, an Fe-efficient hybrid (P3279) released more phytosiderophore from nodal roots than an Fe-inefficient hybrid (P3489). Tests of an additional 10 hybrids showed that phytosiderophore release varied significantly among the cultivars but did not clearly distinguish between hybrids classified as Fe-efficient or Fe-inefficient in individual company trials. We recommend using nodal roots when studying Fe-stress response mechanisms in maize.

Phenotypic expression of different maize hybrid genotypes grown on saline‐sodic soil

Abstract Iron deficiency chlorosis (FeDC) in various degrees affects nearly 500,000 ha of corn (Zea mays L.) in Nebraska, primarily in the river valleys, but also on eroded uplands. Corn hybrids produced from 27 public released and 45 experimental inbreds were grown on a Cozad silt loam, saline‐sodic (Typic Haplustolls). This soil is slightly calcareous with average pH of 8.3, organic matter 1.8%, DTPA‐iron 2.59 ppm, SAR 1.75, and electrical conductivity (EC) of 1.97 in the top 28 cm. Salinity and sodium increase in the next 28 cm with pH at 8.6, SAR 3.44, and EC 2.12. Under these conditions, corn grain yields ranged from 0 to nearly 7600 kg/ha. Yields of the most tolerant hybrids were still only 60–65% of those hybrids grown on a Cozad silt loam with lower salinity and sodium. Susceptibility to FeDC is very genotype specific with the most extreme case being MO17 by N192 yielding 6400 kg/ha, while MO17 by N195 gave 0 yield. Average yield of the six hybrids made with N139 as a parent was 398 kg/ha. Several...

COAL FLY ASH AS AN ACID-REDUCING SOIL AMENDMENT AND ITS SIDE-EFFECTS

Coal combustion by-products may offer significant benefits if used properly to neutralize soil acidity, but unintended release of trace components must be considered. A study was conducted with two objectives: (i) To compare the efficacy of two different preparations of fly ash with that of conventional ag lime for their ability to raise soil pH and reduce exchangeable Al; and (ii) to determine if the Al applied in fly ash produces detrimental changes in soil properties following subsequent acidification. Either fly ash in one of two forms, or conventional ag lime, was applied to three acid soils (Anselmo loam, Valentine sandy loam, and Holdrege sandy loam) in a pot study at rates equal to 0.5, 1.0, and 1.5 times the soils’ lime requirements. Soils were equilibrated in triplicate at approximately 33 kPa water potential in the greenhouse for 315 days (liming phase), during which pH and exchangeable aluminum (Al) were measured. The soils were then acidified under similar conditions for 439 days (acidification phase) by adding dilute acid solution to simulate management-induced acidification, and pH and exchangeable Al were then measured again. Both fly ashes and ag lime were effective in raising soil pH by up to 1.2 units and in reducing exchangeable Al by up to 5.6 mg kg−1. Two-way interactions involving soil, liming material, and rate of application produced different results for combinations of these factors. All amendments helped the soils resist subsequent acidification compared with zero-rate treatments but differed based on the 3-way combinations of soil, liming material, and rate of application. We concluded that overliming (as indicated by exceeding the target pH of 6.5) is a problem with all liming materials on the coarsest soils, suggesting that lime calibration should be re-examined. The fly ash materials seem to contribute to soil exchangeable Al after acidification, but this contribution is inconsequential if soil pH values are maintained at agronomic optima.