Monitoring Nitrogen Status of Corn

The strong relationship between nitrogen (N) availability in soil and crop yields makes N management a primary concern of producers. Over the past several decades, a majority of corn producers have come to regard fertilizer N as the primary source of N nutrition. Most producers acknowledge other sources of N such as manure, legumes, nitrate in water used for irrigation and mineralization of organic matter (microbial conversion of organic N to inorganic N as ammonium and nitrate). Giving credit for non-fertilizer sources of N is a common practice, but the amount of credit is usually conservative because producers are uncertain about when it will become available and how much can be used by the crop. Another reason for only giving minimal N credits is to reduce the risk yield reduction associated with an N deficiency and the general inability to easily correct a deficiency after sidedressing. The exception is where irrigation is available or where producers have access to high clearance vehicles

Post Anthesis Nitrogen Loss from Corn

Nitrogen (N) management practices of corn producers have been called into question because of nitrate contamination problems in surface and ground water. Fertilizer N has been strongly implicated as the major source of much of the nitrate that now exists in our water resources. Cultural practices used in corn production lend themselves to possible nitrate leaching because practical limitations require a majority of the fertilizer N to be applied well ahead of when it can be used by the crop. Nitrogen uptake by corn is anything but uniform throughout the growing season. Little N is used by a corn crop before mid June and by silking in mid to late July 70 to 90% of total N uptake at harvest will already be in the plant. This scenario implies that only 10 to 30% of total N uptake occurs after silking even though the crop accumulates about half of its dry matter after silking. This simple analogy assumes that once N enters the plant it is not lost until the crop matures

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

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

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

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