Yield Response and N-fertilizer recovery of rainfed wheat growing in the Mediterranean region

Yield response and isotopic N-fertilizer recovery of rainfed wheat were assessed as influenced by fertilizer rate and timing. A popular bread wheat cultivar, Seri 82, was planted in a 4-year experiment from 1994/1995 to 1997/1998. Urea fertilizer was applied at rates of 0-240 N ha-1 in two split applications. Fertilizer-N recovery and residual N remaining in the soil after wheat harvest were measured using 15N-labelled fertilizers. The highest wheat grain yield ranged from 4.9 to 6.9 t ha-1 with 240 kg N ha-1 fertilizer. The 4-year results showed that wheat benefited least from the fertilizer applied near planting. N-fertilizer recovery was higher from fertilizer applied during tillering compared with application at emergence. The results suggest that applying one-third or less of the total N at planting and applying the remained at tillering can minimize leaching risks. Another befit of this strategy would be an overall increase in N-fertilizer recovery. Residual fertilizer-N left in soil after wheat harvest was proportional to N application rates and mainly confined t the upper 40 cm depth. 15N recovery by wheat at maturity was 50-60%, indicating that 40-50% of fertilizer-N remained in the soil or was lost. Over 95% of total fertilizer application to wheat could be accounted for in the wheat crop or soil after harvest at the 240 kg N ha-1 rate. The results, therefore, suggest that leaching losses of fertilizer-N below 90 cm were not likely during the growing season for rainfed what grown on these heavy-textured soils (Palexerollic Chromoxeret) of the Mediterranean region

EC03-702 Precision Agriculture: Applications of Remote Sensing in Site-Specific Management

Precision farming is an emerging agricultural technology that involves managing each crop input on a site-specific basis to reduce waste, increase profits, and maintain the quality of the environment. Remote sensing is a technology that can be used to obtain various spatial layers of information about soil and crop conditions. It allows detection and/or characterization of an object, series of objects, or landscape without having the sensor in physical contact

Maize Production Impacts on Groundwater Quality

The cumulative effects of management pratices on nitrate-nitrogen (NO3-N) leaching and groundwater quality are frequently difficult to document because of the time required for expression and the diversity of interacting process involved. This work reports results of a N and water management program initiated by the Central Platte Natural Resource District (CPNRD) in Nebraska. Cultural pratices recommended by the CPNRD and reported by producers for the 1988 growing season, representing approximately 3900 fields and fertilizer N application rates. Groundwater NO3-N concentrations were positively correlated with ressidual N in the surface 0.9 m of soil prior to the growing season, reflecting the effects of past N and water management practices. Yield goals in 1988 averaged 9% higher than the average 10.0 Mg ha-1 in excess of the average N recommendation. By comparison, in a 1980 to 1984 study from an area within the CPNRD, yield goals averaged 28% greater than actual yields. Overly optimistic yield goals in 1988 accounted for 42% of the average excess N application rate 48 kg ha-1 (based on University of Nebraska recommendations). A large portion of average excess N application is attributed to producers in 14% of the area who applied \u3e 100 kg N ha-1 more than the recommened rates. Fertilizer N applied showed little relationship to fertilizer N recommended. Better education and more stringent measures may be required to address the select group of producers who fail to follow CPNRD recommendations

Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years

Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZthat characterize spatial varia- tion in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field.Ageoreferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application tem, of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions

Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years

Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZthat characterize spatial varia- tion in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field.Ageoreferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application tem, of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions

Detection of Phosphorus and Nitrogen Deficiencies in Corn Using Spectral Radiance Measurements

Applications of remote sensing in crop production are becoming increasingly popular due in part to an increased concern with pollution of surface and ground waters due to over-fertilization of agricultural lands and the need to compensate for spatial variability in a field. Past research in this area has focused primarily on N stress in crops. Other stresses and the interactions have not been fully evaluated. A field experiment was conducted to determine wavelengths and/or combinations of wavelengths that are indicative of P and N deficiency and also the interaction between these in corn (Zea mays L.). The field experiment was a randomized complete block design with four replications using a factorial arrangement of treatments in an irrigated continuous corn system. The treatment included four N rates (0, 67, 134, and 269 kg N ha-1) and four P rates (0, 22, 45, and 67 kg P ha-1). Spectral radiance measurements were taken at various growth stages in increments from 350 to 1000 nm and correlated with plant N and P concentration, plant biomass, grain N and P concentration, and grain yield. Reflectance in the near-infrared (NIR) and blue regions was found to predict early season P stress between growth stages V6 and V8. Late season detection of P stress was not achieved. Plant N concentration was best predicted using reflectance in the red and green regions of the spectrum, while grain yield was estimated using reflectance in the NIR region, with the particular wavelengths of importance changing with growth stage

G93-1171 Using a Chlorophyll Meter to Improve N Management

This NebGuide describes how to use a chlorophyll meter as a tool to improve nitrogen management by detecting nitrogen deficiency and determining the need for additional N fertilizer. Fertilizer nitrogen (N) is increasingly recognized as the source of nitrate contamination in much of Nebraska\u27s groundwater. Improving the efficiency of fertilizer N use reduces the amount of N that can potentially contaminate water resources. Effective management of fertilizer N is a major challenge for grain crop producers. Many factors that affect its efficiency are beyond a producer\u27s control. Weather, equipment limitations and breakdowns, and availability of labor and fertilizer during critical periods can lead to inadequate N supply to the crop. Fertilizer N is relatively inexpensive, and deficiencies can result in substantial yield reductions. Producers are inclined to manage fertilizer N to minimize the risk of deficiency, which can lead to excessive fertilizer applications. Although they understand fertilizer applied at excessive rates costs money and may lead to contamination of the environment, producers also want assurance that applying less fertilizer N will not reduce crop yields

A new perspective when examining maize fertilizer nitrogen use efficiency, incrementally

For maize (Zea mays L.), nitrogen (N) fertilizer use is often summarized from field to global scales using average N use efficiency (NUE). But expressing NUE as averages is misleading because grain increase to added N diminishes near optimal yield. Thus, environmental risks increase as economic benefits decrease. Here, we use empirical datasets obtained in North America of maize grain yield response to N fertilizer (n = 189) to create and interpret incremental NUE (iNUE), or the change in NUE with change in N fertilization. We show for those last units of N applied to reach economic optimal N rate (EONR) iNUE for N removed with the grain is only about 6%. Conversely stated, for those last units of N applied over 90% is either lost to the environment during the growing season, remains as inorganic soil N that too may be lost after the growing season, or has been captured within maize stover and roots or soil organic matter pools. Results also showed iNUE decrease averaged 0.63% for medium-textured soils and 0.37% for fine-textured soils, attributable to fine-textured soils being more predisposed to denitrification and/or lower mineralization. Further analysis demonstrated the critical nature growing season water amount and distribution has on iNUE. Conditions with too much rainfall and/or uneven rainfall produced low iNUE. Producers realize this from experience, and it is uncertain weather that largely drives insurance fertilizer additions. Nitrogen fertilization creating low iNUE is environmentally problematic. Our results show that with modest sub-EONR fertilization and minor forgone profit, average NUE improvements of ~10% can be realized. Further, examining iNUE creates unique perspective and ideas for how to improve N fertilizer management tools, educational programs, and public policies and regulations

Use of Remote-Sensing Imagery to Estimate Corn Grain Yield

Remote sensing—the process of acquiring information about objects from remote platforms such as ground-based booms, aircraft, or satellites—is a potentially important source of data for site-specific crop management, providing both spatial and temporal information. Our objective was to use remotely sensed imagery to compare different vegetation indices as a means of assessing canopy variation and its resultant impact on corn (Zea mays L.) grain yield. Treatments consisted of five N rates and four hybrids, which were grown under irrigation near Shelton, NE on a Hord silt loam in 1997 and 1998. Imagery data with 0.5-m spatial resolution were collected from aircraft on several dates during both seasons using a multispectral, four-band [blue, green, red, and near-infrared reflectance] digital camera system. Imagery was imported into a geographical information system (GIS) and then geo-registered, converted into reflectance, and used to compute three vegetation indices. Grain yield for each plot was determined at maturity. Results showed that green normalized difference vegetation index (GNDVI) values derived from images acquired during midgrain filling were the most highly correlated with grain yield; maximum correlations were 0.7 and 0.92 in 1997 and 1998, respectively. Normalizing GNDVI and grain yield variability within hybrids improved the correlations in both years, but more dramatic increases were observed in 1997 (0.7 to 0.82) than in 1998 (0.92 to 0.95). This suggested GNDVI acquired during midgrain filling could be used to produce relative yield maps depicting spatial variability in fields, offering a potentially attractive alternative to use of a combine yield monitor

Herbicide Loading to Shallow Ground Water beneath Nebraska’s Management Systems Evaluation Area

Better management practices can counter deterioration of ground water quality. From 1991 through 1996 the influence of improved irrigation practices on ground water pesticide contamination was assessed at the Nebraska Management SystemsEvaluation Area. Three 13.4-ha corn (Zea mays L.) fields were studied: a conventional furrow-irrigated field, a surge-irrigated field and a center pivot–irrigated field, and a center pivot–irrigated alfalfa (Medicago sativa L.) field. The corn fields received one identical banded application of Bicep (atrazine [6-chloro-N-ethyl-N’-(1-methylethyl)-1,3,5-triazine-2,4,-diamine] _ metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide]) annually; the alfalfa field was untreated. Ground water samples were collected three times annually from 16 depths of 31 multi-level samplers. Six years of sample data indicated that a greater than 50% reduction in irrigation water on the corn management fields lowered average atrazine concentrations in the upper 1.5 m of the aquifer downgradient of the corn fields from approximately 5.5 to –1. Increases in deethylatrazine (DEA; 2-chloro-4-amino-6-isopropyl- amino-s-triazine) to atrazine molar ratios indicated that reducing water applications enhanced microbial degradation of atrazine in soil zones. The occurrence of peak herbicide loading in ground water was unpredictable but usually was associated with heavy precipitation within days of herbicide application. Focused recharge of storm runoff that ponded in the surge-irrigated field drainage ditch, in the upgradient road ditch, and at the downgradient end of the conventionally irrigated field was a major mechanism for vertical transport. Sprinkler irrigation technology limited areas for focused recharge and promoted significantly more soil microbial degradation of atrazine than furrow irrigation techniques and, thereby, improved ground water quality