J. Schepers | University of Nebraska Lincoln (original) (raw)

Papers by J. Schepers

Agronomy Journal, 2008

Midseason fertilizer N recommendations in corn (Zea mays L.) and wheat (Triticum aestivum L.) are... more Midseason fertilizer N recommendations in corn (Zea mays L.) and wheat (Triticum aestivum L.) are not consistent from one region to the next. Preplant soil testing, yield goals, economic optimums, chlorophyll meters, and optical sensor‐based yield prediction models are limited regionally. The objective of this paper is to introduce an applied approach for applying preplant N fertilizer in automated gradients used for determining midseason N rates based on plant response. This approach assumes that midseason biomass estimated using normalized difference vegetation index (NDVI) sensor readings is directly related to corn and wheat grain yield, and that delaying applied N until midseason (eight‐leaf stage in corn and Feekes 5 in winter wheat) can result in near‐maximum yields. The ramped calibration strip (RCS) applicator applies 16 different incremental N rates (3‐to 6‐m intervals), over 45 to 90 m (number of rates, intervals, and distances can be adjusted depending on the crop). Beca...

Agronomy Journal, 2018

Core Ideas Active‐optical reflectance sensor algorithms perform poorly outside the area for which... more Core Ideas Active‐optical reflectance sensor algorithms perform poorly outside the area for which they were originally developed. The red edge waveband is more sensitive to N stress than the red waveband. Some active‐optical reflectance algorithms are dependent on the sensor for which they were developed. Uncertainty exists with corn (Zea mays L.) N management due to year‐to‐year variation in crop N need, soil N supply, and N loss from leaching, volatilization, and denitrification. Active‐optical reflectance sensing (AORS) has proven effective in some fields for generating N fertilizer recommendations that improve N use efficiency, but locally derived (e.g., within a US state) AORS algorithms have not been tested simultaneously across a broad region. The objective of this research was to evaluate locally developed AORS algorithms across the US Midwest Corn Belt region for making in‐season corn N recommendations. Forty‐nine N response trials were conducted across eight states and thr...

Agronomy Journal, 2008

Active sensor reflectance assessments of corn (Zea mays L.) canopy N status are advocated to dire... more Active sensor reflectance assessments of corn (Zea mays L.) canopy N status are advocated to direct variable N applications and improve N use efficiency (NUE). Our goals were to determine: (i) growth stage and (ii) sensor vegetation index with greatest sensitivity in assessing N status and grain yield. Variable crop N was generated by supplying N at different amounts and times in three field studies. Chlorophyll meter (CM) and sensor data were gathered at two vegetative (V11 and V15) and two reproductive (R1 and R3) growth stages, using the Crop Circle sensor that measures reflectance in visible (590 nm) and near infrared (NIR) (880 nm) bands. Sensor data were converted to the normalized difference vegetation index (NDVI590) and chlorophyll index (CI590) values. Grain yields were also determined. Sensor indices were more highly correlated with CM readings for vegetative vs. reproductive growth (r2 of 0.85 vs. 0.55). The CM vs. CI590 slope was over twice the NDVI590 slope value, indi...

Agronomy Monographs, 2015

Remote Sensing of Environment, 2012

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Agronomy Journal, 2004

of fully expanded leaves, n, designated by V n) and reproductive (from silking to physiological m... more of fully expanded leaves, n, designated by V n) and reproductive (from silking to physiological maturity according Monitoring crop phenology is required for understanding intrato the degree of kernel development, designated by R n) and interannual variations of agroecosystems, as well as for improving yield prediction models. The objective of this paper is to remotely stages (Hanway, 1971; Ritchie et al., 1992). Within these evaluate the phenological development of maize (Zea mays L.) in stages, several transitions are important in terms of manterms of both biomass accumulation and reproductive organ appearagement by producers: (i) crop emergence (date of onset ance. Maize phenology was monitored by means of the recently develof photosynthetic activity, termed VE), (ii) tasseling oped visible atmospherically resistant indices, derived from spectral (date when maximum leaf area is attained and maize reflectance data. Visible atmospherically resistant indices provided tassels emerge, termed VT), and (iii) initiation of senessignificant information for crop phenology monitoring as they allowed cence (date at which green leaf area visibly begins to us to detect: (i) changes due to biomass accumulation, (ii) changes decrease). To maximize yields, the plants need, on a induced by the appearance and development of reproductive organs, per-stage basis, to optimize the supply of nutrients and and (iii) the onset of senescence, earlier than widely used vegetation to be maintained under favorable environmental condiindices. Visible atmospherically resistant indices allowed the identification of the timing of phenological transitions that are related to the tions (i.e., temperature, solar radiation, soil moisture). maize physiological development. They also allowed identification of Unfavorable conditions occurring between crop emerthe onset of the grain-fill period, which is important since maximum gence and leaf development will limit the size of the yield potential of maize plants depends on optimal environmental leaves and thus the amount of photosynthetic biomass conditions during this period.

Journal of Environmental Quality, 2003

Atrazine is the most widely detected pesticide in the nation's ground water and the USEPA has set... more Atrazine is the most widely detected pesticide in the nation's ground water and the USEPA has set 3 g L Ϫ1 Better management practices can counter deterioration of ground as the maximum contaminant level (MCL) in drinkwater quality. From 1991 through 1996 the influence of improved irrigation practices on ground water pesticide contamination was assessed ing water. at the Nebraska Management Systems Evaluation Area. Three 13.4-ha Generally, nonpoint-source loading of pesticides in corn (Zea mays L.) fields were studied: a conventional furrow-irrigated shallow ground water beneath agricultural fields is visufield, a surge-irrigated field and a center pivot-irrigated field, and a alized as a complex, nonuniform network of macropores center pivot-irrigated alfalfa (Medicago sativa L.) field. The corn fields conveying contaminants through the vadose zone to the received one identical banded application of Bicep (atrazine [6-chlorowater table where high input concentrations are par-N-ethyl-N-(1-methylethyl)-1,3,5-triazine-2,4,-diamine] ϩ metolachlor tially masked by vertical and radial dilution. The major-[2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) ity of loading has been attributed to the transfer, mixing, acetamide]) annually; the alfalfa field was untreated. Ground water application, and disposal or "routine use" of pesticides samples were collected three times annually from 16 depths of 31 multiin agriculture. Hallberg (1989), however, points out that level samplers. Six years of sample data indicated that a greater than 50% reduction in irrigation water on the corn management fields low-the contamination may be attributable to a wider specered average atrazine concentrations in the upper 1.5 m of the aquifer trum of management variables that, while standard pracdowngradient of the corn fields from approximately 5.5 to Ͻ0.5 g tices for the user, are beyond the scope of officially L Ϫ1. Increases in deethylatrazine (DEA; 2-chloro-4-amino-6-isopropylrecognized normal use and more likely to impair ground amino-s-triazine) to atrazine molar ratios indicated that reducing wawater quality. The effects of structures for the retention ter applications enhanced microbial degradation of atrazine in soil and reuse of water especially in furrow-irrigated agriculzones. The occurrence of peak herbicide loading in ground water was ture have been overlooked and could be responsible for unpredictable but usually was associated with heavy precipitation much of the shallow ground water loading of pesticides within days of herbicide application. Focused recharge of storm runoff routinely applied to fields. While ground water assessthat ponded in the surge-irrigated field drainage ditch, in the upgraments have become the basis for USEPA's regulatory dient road ditch, and at the downgradient end of the conventionally irrigated field was a major mechanism for vertical transport. Sprinkler strategy of developing state Pesticide Management Plans irrigation technology limited areas for focused recharge and promoted for atrazine, cyanazine, simazine, alachlor, and metolasignificantly more soil microbial degradation of atrazine than furrow chlor (Federal Register, 1996), they have done little to exirrigation techniques and, thereby, improved ground water quality. plain the transport mechanisms of pesticides to shallow ground water and the large temporal variability of the concentrations. Long-term field-scale studies addressing Concentrations of DIA, a metabolite of atrazine, si-Center-pivot corn 335 mazine, and cyanazine, exceeded the reporting limit

Quem acompanhou as novas tecnologias antes da virada do milenio, ouviu falar muito em Agricultura... more Quem acompanhou as novas tecnologias antes da virada do milenio, ouviu falar muito em Agricultura de Precisao. Foram-nos apresentadas maquinas sofisticadas como sinonimo da modernidade no campo. Para muitos desavisados a Agricultura de Precisao era o advento da automacao no campo, mas para quem pode observar de perto, era uma nova maneira de enxergar o campo. Era a oportunidade de um produtor que ja estava na lideranca tecnologica poder fazer ainda melhor.

Precision Agriculture, 2005

Bare soil reflectance from airborne imagery or laboratory spectrometers has been used to infer so... more Bare soil reflectance from airborne imagery or laboratory spectrometers has been used to infer soil properties such as soil texture, organic matter, water content, salinity and crop residue cover. However, the relation of soil properties to reflectance data often varies with soil type and conditions and surface reflectance may not be representative of the conditions in the root zone. The objectives of this study were to assess the soil reflectance data obtained by ground-based sensors and to model soil properties in the root zone as a function of surface soil reflectance and plant response. Ground-based sensors were used to simultaneously monitor soil and canopy reflectance in the visible and near-infrared (VNIR) along six rows and in two growth stages in a 7 ha cotton field. The reflectance data were compared to soil properties, leaf nutrients and biomass measured at 33 sampling positions along the rows. Brightness values of the blue and green bands of soil reflectance were better correlated to soil water content, particulate organic matter and extractable potassium and phosphorus, while those in the red and NIR bands were correlated to soil carbonate content, total nitrogen, electrical conductivity and foliar nutrients. The correlation of red soil reflectance with canopy reflectance was significant and indicated an indirect inverse relationship between soil fertility and plant stress. The integration of surface soil reflectance and plant response variables in a multiple regression model did not substantially improve the prediction of soil properties in the root zone. However, crop nutrient status explained a significant portion of the spatial variability of soil properties related to nitrification processes when soil reflectance did not. The implication of these findings to agricultural management is discussed.

Journal of Plant Nutrition, 2006

Information on the contribution of various soil nitrogen (N) sources to plant N uptake is often n... more Information on the contribution of various soil nitrogen (N) sources to plant N uptake is often needed for the implementation of sustainable or site-specific management practices in agriculture. Considering the limitations of traditional methods in meeting these needs, this study investigated the potential of leaf δ 15 N as an early indicator of nutrient deficiency in cotton. The spatial and temporal natural abundance of 15 N was measured in the soil and leaves of a fertilized cotton field located near the village of Moschochori (Larissa, Greece). The isotopic signal of the leaves was interpreted in the context of the relative contribution of fertilizer to cotton N uptake,as has been demonstrated in the past for other agricultural crops such as wheat (Triticum aestivam L.) and corn (Zea mays). Spatial variability of leaf δ 15 N was high early in the growing season (June), reflecting differences in fertilizer N availability and uptake between the east and west side of the field, as well as differences resulting from soil denitrification in depressions. The west side of the field appears to have lost significant amounts of fertilizer N, due to leaching during the rainy period in May, that accumulated in depressions near the waterway. In the subsequent months, the isotopic signal of the leaves was consistently high and indicated reduced fertilizer N uptake on the west side that resulted in deficiencies of N as well as of phosphorus (P) and potassium (K). The significant correlations of mid-square leaf δ 15 N with late-season nutrient content and soil elelctrical conductivity(EC) provided evidence that the natural abundance of 15 N was a sensitive indicator of soil and plant nutrient status in this fertilized cotton field.

Field Crops Research, 2001

Agronomy Abstracts, 2007

In-season nitrogen management for corn is a challenge because the crop is growing rapidly and act... more In-season nitrogen management for corn is a challenge because the crop is growing rapidly and active sensors, as well as imagery, have difficulty penetrating very deep into the canopy. Remote sensing technologies strive to evaluate plant chlorophyll status (greenness) as ...

Agronomy Journal, 2018

Active-optical reflectance sensors (AORS) use light reflectance characteristics from a crop canop... more Active-optical reflectance sensors (AORS) use light reflectance characteristics from a crop canopy as an indicator of the plant's N health. However, studies have shown AORS algorithms used in conjunction with measured reflectance characteristics for corn (Zea mays L.) N fertilizer rate recommendations are not consistently accurate. Our objective was to determine if soil and weather information could be utilized with an AORS algorithm developed at the University of Missouri (ALG MU) to improve in-season (~V9 corn development stage) N fertilizer recommendations. Nitrogen response trials were conducted across eight states over three growing seasons, totaling 49 sites with soils ranging in productivity. Nitrogen fertilizer rates according to the ALG MU were compared to economic optimal nitrogen rate (EONR). Without soil and weather information included, the root mean square error (RMSE) of the difference between ALG MU and EONR (MU DIFF) was 81 and 74 kg N ha-1 for treatments receiving 0 and 45 kg N ha-1 applied at planting, respectively. When ALG MU was adjusted using weather (seasonal precipitation and distribution prior to sidedress) and soil clay content, the RMSE was reduced by 24 to 26 kg N ha-1. Without adjustment, 20 and 29% of sites were within 34 kg N ha-1 of EONR with 0 and 45 kg N ha-1 at planting, respectively. But with adjustment for soil and weather data, 45 and 51% of sites were within 34 kg N ha-1 of EONR. These results show that weather and soil information could be used to improve ALG MU N recommendation performance.

Photogrammetric Engineering & Remote Sensing, 2003

This review addresses the challenges and progress in sensor development and radiometric correctio... more This review addresses the challenges and progress in sensor development and radiometric correction for agricultural applications with particular emphasis on activities within the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS). Examples of sensor development include on-site development of sensors and platforms, participation in cooperative research and development agreements (CRADA) with commercial companies, and membership on NASA science teams. Examples of progress made in sensor radiometric correction suitable for agriculture are presented for both laboratory and field environments. The direction of future sensor development includes integrated sensors and systems, sensor standardization, and new sensor technologies measuring fluorescence and soil electrical conductivity, and utilizing LIght Detection and Ranging (lidar), hyperspectral, and multiband thermal wavelengths. The upcoming challenges include definition of the core spectral regions for agriculture and the sensor specifications for a dedicated, orbiting agricultural sensor, determination of an operational approach for reflectance and temperature retrieval, and enhanced communication between image providers, research scientists, and users. This review concludes with a number of avenues through which USDA could promote sensor development and radiometric correction for agricultural applications. These include developing a network of large permanent calibration targets at USDA ARS locations; investing in new technologies; pooling resources to support large-scale field experiments; determining ARS-wide standards for sensor development, calibration, and deployment; and funding interagency agreements to achieve common goals.

Impacts of Animal Manure Management on Ground and Surface Water Quality A. Sharpley, JJ Meisinger... more Impacts of Animal Manure Management on Ground and Surface Water Quality A. Sharpley, JJ Meisinger, A. Breeuwsma, JT Sims, TC Daniel, and JS Schepers 1. 1ntroduction 173 11. Groundwater Quality 179 A. Nitrogen Budgets 179 B. Phosphorus Movement 186 111. Surface Water ...

Journal of Environment Quality, 2001

Groundwater quality beneath irrigated vegetable fields in a north-central U.S. sand plain. J. Env... more Groundwater quality beneath irrigated vegetable fields in a north-central U.S. sand plain. J. Environ. gen timing and irrigation methods on Russet Burbank Potatoes.

Soil electrical conductivity (EC) is a useful indicator in managing agricultural systems, but too... more Soil electrical conductivity (EC) is a useful indicator in managing agricultural systems, but tools for convenient and inexpensive measurements in the field are generally lacking. Handheld conductivity probes were designed to evaluate in-field naturally occurring and human-induced total soluble electrolyte levels in soil and water. The probes were used to survey and monitor EC in the field and to assess soil and water quality as related to environmental stability and sustainable food production. A pencil-sized 16-cm probe (PP) was connected to a handheld Hanna (DiST WP 4) conductivity meter, resulting in an economical, compact, and easy to use device. The tool provided accurate and precise results compared with laboratory instrumentation under standardized conditions of soil water content and temperature. Soil samples, varying widely in texture and organic matter content, and having ECs ranging from 0.13 to 2.32 dS m 21 were used for comparison. Mean values and coefficients of variation were similar for the PP and the commercial laboratory EC meter with values determined with the two instruments being strongly correlated (r 2 ¼ 0.96-0.99). The handheld and PP probes effectively replaced expensive and cumbersome laboratory and field instruments used to measure EC in water and soil samples. The

Current methods for determining midseason nitrogen (N) rates in corn have used normalized differe... more Current methods for determining midseason nitrogen (N) rates in corn have used normalized difference vegetation index (NDVI), and in some cases, plant height and intra-specific plant competition. Another parameter that can be linked to potential yield is stalk diameter; thus incorporating collectively the parameters of NDVI, plant height, and stalk diameter should result in a better prediction of yield potential. This could lead to more efficient methods for midseason fertilizer N applications. The objective of this study was to analyze the relationship of stalk diameter, as well as plant height and NDVI, with final grain yield, and to refine the method of predicting yield potential using a combination of these factors. In this 2-year study at 4 locations, we selected several rows of corn plants, each with varying amounts of pre-plant nitrogen fertilizer, from 0 to 145 kg ha-1 , and where no additional nitrogen was applied throughout the growing season. Measurements of plant spacing, stalk diameter, plant height, and NDVI were taken from growth stages V8 (eight fully collared leaves) to VT (corn tasselling), and all corn plants were harvested by-plant to determine grain yield or dry biomass. Individual plant height measurements proved to be a good predictor of by-plant grain yield (r 2 = 0.52, 0.53; V10, V12, respectively). Using a value of stalk diameter X plant height gave the best correlation with grain yield (r 2 = 0.34, 0.55, 0.67; V8, V10, V12, respectively). By-plant biomass was also highly correlated with stalk diameter, with an r 2 of 0.68 at growth stage V15, using a polynomial function. This work showed that stalk diameter X plant height

… and electronics in …, 2008

This article was published in an Elsevier journal. The attached copy is furnished to the author f... more This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author's institution, sharing with colleagues and providing to institution administration. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Agronomy Journal, 2008

Agronomy Journal, 2018

Agronomy Journal, 2008

Agronomy Monographs, 2015

Remote Sensing of Environment, 2012

Agronomy Journal, 2004

Journal of Environmental Quality, 2003

Precision Agriculture, 2005

Journal of Plant Nutrition, 2006

Field Crops Research, 2001

Agronomy Abstracts, 2007

Agronomy Journal, 2018

Photogrammetric Engineering & Remote Sensing, 2003

Journal of Environment Quality, 2001

… and electronics in …, 2008