Long-Term Variable Rate Lime and Phosphorus Application for Piedmont No-Till Field Crops

Variable rate (VR) fertilizer application is a paradigm with potential to improve input efficiency and farm profitability. It is widely marketed by commercial applicators in the southeastern US. However, field studies comparing VR with traditional management have not demonstrated consistent, positive results. The objectives of this study were: (1) to determine the soil impact, crop response and economic potential of VR phosphorus (P) and lime application in a North Carolina Piedmont no-till field crop system using intensive soybean [Glycine max (L.) Merr.] production and (2) to economically evaluate alternatives to standard commercial grid soil sampling for directing VR P and lime. A 23-ha long-term no-till field in the SE Piedmont was divided into 0.4ha plots assigned to either VR or uniform P and lime application. Grid soil sampling and VR P and lime application were done prior to four crops over 3 years: full season soybean, wheat (Triticum aestivum L.)–double cropped soybean, and full season soybean. Soil test P, pH and crop yield response to VR P were inconsistent. Soil pH in areas with low pH initially did increase in response to VR lime, but it took two to three applications to bring all of these areas to the target pH. Once VR-liming raised initially low soil pH to levels close to target, yield of soybean, but not wheat, were up to 0.74Mgha^–1 higher than with uniform lime. Even with significantly higher soybean yields associated with VR lime, 3 years of grid sampling and VR application were not profitable compared to uniform application. The results indicated that VR lime could be profitable if the initial grid sampling data were used either for 2 consecutive years, or if it was used to restrict future grid sampling to specific areas requiring further VR lime.     

基于光谱指数的冬小麦变量施肥冠层光谱特征研究及产量分析

 【目的】由适时获得的高光谱数据代替传统繁琐的实验室土壤养分测定数据来进行变量施肥，实现冬小麦高产优质的目标。【方法】本研究利用冬小麦起身期和拔节期冠层光谱数据，选用反映冬小麦长势信息的优化土壤调节植被指数（OSAVI，optimization of soil-adjusted vegetation index）和变量施肥模型进行变量施肥管理（变量区），以相邻地块常规非变量（均一）施肥区（对照区）为对照，研究了不同氮肥处理冬小麦冠层光谱特征及其施肥效应。【结果】变量施肥之后两种氮肥处理在敏感波段670 nm和760～900 nm处反射率差异明显，而670nm和760～900nm是氮素和冠层的敏感波段，说明进行变量施肥时，利用基于这两个波段组合的光谱指数OSAVI优于其它波段组合的光谱指数；SAVI不同生育时期的变化情况，反映了变量施肥在调控作物长势及群体结构上的优势；与对照区相比变量区提高产量达378.72 kg•ha-1，并降低了各小区产量之间的变异,变量区土壤硝态氮浓度降低，氮肥利用率提高，生态效益较为明显。【结论】该技术通过改善冬小麦群体质量，延缓了植株衰老，促进干物质和氮积累，增加冬小麦产量和氮肥利用率。     

Severity,Extent and Persistence of Spatial Yield Variation in Production Fields in the SE US Coastal Plain

In the US SE Coastal Plain, adoption of site-specific farming has lagged behind that in the upper Midwest. While reasons for this may be both social and economic, it appears that the importance of the problem represented by yield variation on production fields needs to be quantified before adoption would be considered by many farm operators. Our objective was to document the severity, extent and persistence of yield variation for corn, wheat and soybean during normal production in this region. Farmer combines were fitted with commercial yield monitors to produce yield maps. Corn, wheat and soybean yields were mapped for three years on more than 4900 ha (12,000 acres). For each cooperator, crop and year, summary statistics and cumulative yield distribution functions were also developed. Yield maps showed that substantial areas had yields either well below or above the mean for the cooperator-crop-year. For instance, 25% of Cooperator A’s area had corn yields more than 30% below the mean yield of 5.06 Mg/ha and another 25% had yields more than 31% above that mean, which indicate the severity of yield variation. Variation from county to county had no consistent difference indicating that the extent of the variation is widespread. Variation was also persistent from year to year, with more than 50% of the area in 15 of 17 fields having stable yields relative to the field mean. These data show the potential importance of variable-rate management in the region and also hint at the potential environmental implications.     

Long-term impact of a precision agriculture system on grain crop production

Research is lacking on the long-term impacts of field-scale precision agriculture practices on grain production. Following more than a decade (1993–2003) of yield and soil mapping and water quality assessment, a multi-faceted, ‘precision agriculture system’ (PAS) was implemented from 2004 to 2014 on a 36-ha field in central Missouri. The PAS targeted management practices that address crop production and environmental issues. It included no-till, cover crops, growing winter wheat (Triticum aestivum L.) instead of corn (Zea mays L.) for field areas where corn was not profitable, site-specific N for wheat and corn using canopy reflectance sensing, variable-rate P, K and lime using intensively grid-sampled data, and targeting of herbicides based on weed pressure. The PAS assessment was accomplished by comparing it to the previous decade of conventional, whole-field corn-soybean (Glycine max L.) mulch-tillage management. In the northern part of the field and compared to pre-PAS corn, relative grain yield of wheat in PAS was greatly improved and temporal yield variation was reduced on shallow topsoil, but relative grain yield was reduced on deep soil in the drainage channel. In the southern part of the field where corn remained in production, PAS did not lead to increased yield, but temporal yield variation was reduced. Across the whole field, soybean yield and temporal yield variation were only marginally influenced by PAS. Spatial yield variation of all three crops was not altered by PAS. Therefore, the greatest production advantage of a decade of precision agriculture was reduced temporal yield variation, which leads to greater yield stability and resilience to changing climate.     

长期施肥对砂姜黑土作物产量及土壤物理性质的影响

【目的】保持和提高土壤肥力,提升土壤生产力,是农业持续发展的重要内容。研究无机肥与牛粪、猪粪和小麦秸秆长期配合施用对砂姜黑土作物产量及土物理性质的影响,为培肥改良砂姜黑土、提升砂姜黑土生产力提供理论依据。【方法】利用1982年建立在安徽省蒙城县砂姜黑土上的长期定位试验,分析牛粪、猪粪、秸秆等不同有机物料与无机肥料配施对作物产量、土壤容重和土壤田间持水量的影响,评价有机物料与无机肥配施对砂姜黑土的培肥效果。【结果】长期不施肥处理的小麦、大豆产量持续下降,平均年降低分别为39.0和70.9 kg·hm^-2,25年后产量在极低水平波动。单施无机肥或无机肥与有机物料配施,小麦产量均呈逐年增高的趋势。无机肥和有机物料配施的处理与单施无机肥（NPK）处理相比均表现出增产效果,年均增产率在5%以上。不同有机物料处理间的增产效果是牛粪处理（NPK+CM）优于猪粪处理（NPK+PM）,而猪粪处理优于秸秆处理（NPK+S）。小麦、大豆产量年际间波动幅度较大,长期不施肥处理小麦产量变异系数（CV）最高,增施肥料可以降低CV,有机物料和无机肥配施的处理CV低于单施无机肥处理,牛粪处理CV最小。牛粪、猪粪、秸秆与无机肥料长期配合施用能降低砂姜黑土土壤容重,显著提高土壤田间持水量,小麦、大豆产量与土壤容重呈显著负相关,与土壤田间持水量呈显著正相关,有机物料与无机肥配施可以改善砂姜黑土不良的物理性状。【结论】长期均衡施用无机肥料或有机物料与无机肥配施均能提高土壤肥力水平,小麦产量呈逐年增高的趋势。有机物料与无机肥配施能提高作物产量,降低产量变异,增强产量稳定性,作物高产稳产;能改善砂姜黑土不良的物理性状,提高土壤肥力。有机物料与无机肥配施是安徽省砂姜黑土地区较为适宜的施肥模式。     

Method for Precision Nitrogen Management in Spring Wheat: II. Implementation

By accounting for spatial variation in soil N levels, variable-rate fertilizer application may improve crop yield and quality, and N use efficiency within fields. The main purpose of this study was to demonstrate how site-specific wheat yield and protein data, and a geographic information system may be used in developing precision N-recommendations for spring wheat. The three steps in the procedure include: (1) estimate the amount of N-removed in wheat in the year in which the crop is harvested, (2) estimate the N-deficit, defined as the amount of additional N needed for raising protein concentration in a future crop to a specified target level, and (3) estimate the total N-recommendation by summing the mapped values of the N-removed and the N-deficit. A map for variable-rate application of fertilizer is derived by specifying cutoff values to divide the range in the total N-recommendation into classes representing N management zones.A field experiment was conducted within an annually cropped wheat field (101 ha) in northern Montana to determine whether the proposed method could improve grain yields and protein levels. The N-removal and N-deficit were estimated from site-specific wheat yield and protein data that were acquired during harvest of 1996. In 1997, which was a dry year, an experiment was conducted in the same field that consisted of a randomized complete block design arranged as pairs of strip plots. Variable- or uniform-rate N treatments were randomly assigned to each pair of strips. Both treatments received nearly the same amount of fertilizer, however, N in the variable treatment was varied to match patterns in grain yield and protein levels that previously existed in 1996. Yields were not significantly different between management systems, but proteins were significantly enhanced by spatially variable N application. In addition, variability in protein levels was reduced within the whole field. Field areas deficient in N fertility could be identified without having to sample for soil profile N.     

A Model for Agro-Economic Analysis of Soil pH Mapping

Core soil sampling followed by laboratory analysis is the traditional method used to map soil pH prior to variable rate application (VRA) of lime on cropland. A recently developed automated soil sampling system capable of measuring soil pH on-the-go has significantly increased sampling resolution. However, adoption of such systems must be justified economically. This paper presents a method for assessing the economic benefit from automated mapping of soil pH prior to variable rate lime application. In this work, geostatistical, agronomic, and economic methods were used to generate a comprehensive numerical model for quantitative assessment of the net return over cost of liming for different lime management strategies. The strategies included: automated pH mapping, manual grid soil sampling, and whole field sampling used in combination with either variable or fixed rate liming. The model was demonstrated using a simulated field with known average pH and semivariogram model. The analysis showed the largest benefit ($6.13ha^–1year^–1) from using VRA with automated soil pH mapping versus VRA based on 1ha (2.5acres) manual grid point sampling for the selected simulated field conditions. A sensitivity analysis demonstrated that for a wide range of field conditions and crop prices, VRA plus automated mapping promises higher relative benefits than VRA based on either manual grid point or grid cell sampling.     

Economic and Environmental Evaluation of Variable Rate Nitrogen and Lime Application for Claypan Soil Fields

Variable Rate Technology (VRT) has the potential to increase crop yields and improve water quality relative to Uniform Rate Technology (URT). The effects on profitability and water quality of adopting VRT for nitrogen (N) and lime were evaluated for corn production on four claypan soil fields in north central Missouri under average to better than average weather conditions. Variable N and lime rates were based on measured topsoil depth and soil pH, respectively. VRT rates were compared to two different uniform N applications (URT-Nl based on the topsoil depth within these claypan soil fields, and URT-N2 based on a typical N rate for corn production in this area). Expected corn yield was predicted based on topsoil depth, soil pH, N rate, and lime rate. Water quality benefits of VRT relative to URT were evaluated based on potential leachable N. Sensitivity analyses were performed using simulated topsoil data for topsoil depth and soil pH. Results showed that VRT was more profitable than URT in the four sample fields under URT-N1, and in two of the four fields under URT-N2. Greater variation in topsoil depth and soil pH resulted in higher profitability and greater water quality benefits with VRT. Results support adoption of VRT for N and lime application for other claypan soil fields with characteristics similar to those in the fields used in this study.     

Profitability of variable rate nitrogen application in wheat production

Using plant sensing to determine the amount of nitrogen (N) to apply has the potential to increase profits in wheat (Triticum aestivum) production by reducing N cost or by increasing grain yield. The objective of this paper was to determine if yields and profits from experimental trials that used a precision N applicator to apply N were significantly different from trials that applied pre-determined amounts of N. Across Oklahoma, USA, experiments were designed to test 10 N treatments that included two variable rate treatments (VRT), two uniform rate treatments (URT) where the level of N applied was based on optical reflectance measurements (ORM), and six conventional treatments (i.e., pre-determined uniform rates of N). Data included treatments during 2005–2009 from eight different locations. Results indicated no statistical difference in yields between the conventional treatments that apply 90 kg ha⁻¹ of N and the VRT and URT treatments. On average, the conventional treatment that applied 90 kg ha⁻¹ of top-dress N produced the largest yield, with a VRT treatment producing the third largest yield. Profits were calculated for each treatment using a partial budget. On average, the treatment that received 90 kg ha⁻¹ of top-dress N was the most profitable even though the pre-plant N (anhydrous ammonia) had a cost advantage relative to top-dress N (urea and ammonium nitrate).     

A variable-rate decision support tool

Profitable precision or variable application of inputs depends on many factors; however, the inherent variability in a soil and or crop property and the relative responsiveness of yield to fertilizer inputs at different soil concentration levels are the most important factors in influencing economic gain. Generally, the greater is the spatial variation in the property influencing the input rate, the greater is the potential economic return from precision application compared to uniform application of an input. Based on a quantitative assessment of the spatial variation in soil properties that influence rates of input, a variable-rate decision support tool (VRDST) was developed to: (1) assess the potential profitability of variable-rate compared to uniform application and (2) identify the economic optimal uniform application rate if this is selected. The VRDST was evaluated using spatially distributed soil data from selected fields in North Carolina. Net return from variable-rate application and the economically optimal uniform rates are illustrated. Varying fertilizer cost, crop price and sampling costs greatly influenced net return from variable-rate application.     

Method for Precision Nitrogen Management in Spring Wheat: I Fundamental Relationships

Wheat (Triticum aestivum L.) fields in the semi-arid Northern Great Plains are spatially variable in soil N fertility and crop productivity. Consequently, there is interest in applying variable, rather than uniform rates of fertilizer N across the landscape. Intensive soil sampling as a basis for variable-rate fertilizer management is too costly when compared to the value of wheat in this region. The objective of this research was to determine relationships between yield and protein, and protein and available N as needed to develop a cost-effective variable-rate N fertilizer strategy for spring wheat. A three-year study (1996–1998) was carried out at a site near Havre, Montana, USA (48°30N, 109°22W). Treatments consisted of three water regimes, four cultivars, and five fertilizer N levels per water regime in a randomized complete block design with four replicates. Scatter diagrams of relative yield vs. grain protein were consistent with earlier investigators, and indicated protein concentrations at harvest provided a method for indexing N nutrition adequacy (deficiency vs. sufficiency) in wheat. A critical protein concentration of 13.2% was defined using a graphical Cate-Nelson analysis. This value appeared to be consistent across the three water regimes and four cultivars as 159 (88%) of the 180 water×cultivar×N level episodes were in positive quadrants. No correlation could be found between relative yield and protein for episodes below the critical level (r²=0.1). Hence, grain protein concentrations could not be used to predict the magnitude of yield losses from N deficiency. Grain protein content would be useful for prescribing fertilizer recommendations where N deficiency (<13.2% protein) reduces grain yield under semi-arid conditions. Inverse slopes (dy/dx) of the protein-available N curves reveal that it takes 12–18 kg N/ha to change protein 1% (e.g., 12% vs. 13%) where wheat is under water stress during grain fill. The total N requirement could then be computed by summing the N required for raising protein and the N removed by the crop in the year when the grain was harvested.     

Field methods for making productivity classes for site-specific management of wheat

Reducing the decision-making unit to classes within fields can improve yields, efficiency in the use of nutrients and profitability of crops. The objectives were to compare methods for class delimitation in wheat (Triticum aestivum L.) crops based on apparent productivity levels and establish similarities among them in terms of spatial overlapping, productive attributes and the use of nitrogen. In three wheat fields, high and low apparent productivity classes (APC) were defined based on eight methodologies: yield maps, soil maps, gramineae vegetation index, rotation crop index, interpretation of satellite images, management records, elevation and integrated soil and yield maps. In each APC, soil and crop yield components were determined under five nitrogen fertilization levels. Among delimitation methodologies, the degree of coincidence varied from 1.4 to 81.7%. The differences in soil properties, nitrogen use efficiency and grain yields were greater among fields than among APC within each field. In each field, the delimitation methodologies identified different single factors that discriminated among the potential management classes and were partially associated with the crop grain yields. The wheat crops at the low APC yielded 39% less and 12% less than at the high APC, respectively. The nitrogen fertilization, at the rate for maximum productivity for each ACP, reduced the yield differences between contrasting APC. Nitrogen fertilization also modified clustering of classes based on expected yields. Making management classes for wheat based on expected productivity is more accurate when based on previous crop production information under similar nitrogen fertilization conditions than the targeted crop.

     

河套灌区地膜春小麦适宜播种量研究

为促进河套灌区地膜春小麦生产并实现精量播种,设置不同的穴播量,监测露地直播春小麦(对照)和地膜覆盖穴播春小麦的生长性状和经济性状。结果表明:地膜覆盖春小麦较露地直播的早出苗7 d,早分蘖5 d,早抽穗5 d,早成熟4 d。地膜覆盖春小麦的分蘖力高于露地直播,但分蘖成穗力则与露地直播的基本一致。与露地直播春小麦相比,地膜覆盖春小麦的株高较高,茎秆较粗,单茎生物量较高,根系分布较浅。地膜覆盖春小麦的单茎根系生物量在扬花期前高于露地直播,扬花期后则低于露地直播。地膜覆盖春小麦的单穴茎数、单穴生物量及单穴根系生物量高于露地直播,但根冠比却低于露地直播。露地直播春小麦以穴播14粒的产量最高,地膜覆盖的以穴播12粒的产量最高。相同穴播量下地膜覆盖春小麦的产量高于露地直播,千粒重和经济系数则低于露地直播。河套灌区地膜覆盖春小麦的适宜穴播量为10～12粒,即为常规露地条播量的70%～84%。     

Replicability of nitrogen recommendations from ramped calibration strips in winter wheat

Ramped calibration strips have been suggested as a way for grain producers to determine nitrogen needs more accurately. The strips use incrementally increasing levels of nitrogen and enable producers to conduct an experiment in each field to determine nitrogen needs. This study determines whether predictions from the program Ramp Analyzer 1.2 are replicable in Oklahoma hard red winter wheat (Triticum aestivum). Predictions are derived from 36 individual strips from on-farm experiments—two pairs of adjacent strips at each of nine winter wheat fields in Canadian County, OK. The two pairs of strips within each field were between 120 and 155 m apart. Each strip was analyzed three times during the 2006–2007 growing season. Nitrogen recommendations from Ramp Analyzer 1.2 are not correlated even for strips that were placed side by side, and recommendations from strips in the same field show no more homogeneity than randomly selected strips throughout the county. The results indicate that ramped calibration strips are unlikely to produce accurate nitrogen requirement predictions at any spatial scale, whether at the county level or for subsections of a single field. In contrast, a procedure that uses only measures from the plot with no nitrogen and the plot with the highest level of nitrogen applied does show replicability. Thus, improvements in the ramped calibration strip technology are needed if it is to become viable.     

华北旱作区夏播单间作种植模式吸氮效果及后茬效应

为筛选能够降低土壤硝态氮残留量并具有显著经济效益的华北旱作区夏播种植模式,在河北省徐水县设置夏播作物的不同单间作模式田间对比试验.结果显示,各处理中,玉米大豆间作的作物总吸氮量最大,使土壤硝态氮残留量明显降低并有较好的经济效益,其土地当量比也大于1,且在提高后茬冬小麦籽粒产量、秸秆产量、作物吸氮量方面效果较好.与玉米单作比较,玉米大豆间作模式0～200 cm土层硝态氮残留量降低56.66 kg· hm-2,作物整体吸氮量提高6.17 kg·hm-2,经济效益增加2 054.62元·hm-2;后茬冬小麦的籽粒产量、秸秆产量、作物吸氮量分别提高了197、673 kg· hm-2和5.91 kg· hm-2.     

Decomposing variation in dairy profitability: the impact of output, inputs, prices, labour and management

The UK dairy sector has undergone considerable structural change in recent years, with a decrease in the number of producers accompanied by an increased average herd size and increased concentrate use and milk yields. One of the key drivers to producers remaining in the industry is the profitability of their herds. The current paper adopts a holistic approach to decomposing the variation in dairy profitability through an analysis of net margin data explained by physical input-output measures, milk price variation, labour utilization and managerial behaviours and characteristics. Data are drawn from the Farm Business Survey (FBS) for England in 2007/08 for 228 dairy enterprises. Average yields are 7100 litres/cow/yr, from a herd size of 110 cows that use 0·56 forage ha/cow/yr and 43·2 labour h/cow/yr. An average milk price of 22·57 pence per litre (ppl) produced milk output of ￡1602/cow/yr, which after accounting for calf sales, herd replacements and quota leasing costs, gave an average dairy output of ￡1516/cow/yr. After total costs of ￡1464/cow/yr this left an economic return of ￡52/cow/yr (0·73 ppl) net margin profit. There is wide variation in performance, with the most profitable (as measured by net margin per cow) quartile of producers achieving 2000 litres/cow/yr more than the least profitable quartile, returning a net margin of ￡335/cow/yr compared to a loss of ￡361/cow/yr for the least profitable. The most profitable producers operate larger, higher yielding herds and achieve a greater milk price for their output. In addition, a significantly greater number of the most profitable producers undertake financial benchmarking within their businesses and operate specialist dairy farms. When examining the full data set, the most profitable enterprises included significantly greater numbers of organic producers. The most profitable tend to have a greater reliance on independent technical advice, but this finding is not statistically significant. Decomposing the variation in net margin performance between the most and least profitable groups, an approximate ratio of 65:23:12 is observed for higher yields: lower costs: higher milk price. This result indicates that yield differentials are the key performance driver in dairy profitability. Lower costs per cow are dominated by the significantly lower cost of farmer and spouse labour per cow of the most profitable group, flowing directly from the upper quartile expending 37·7 labour h/cow/yr in comparison with 58·8 h/cow/yr for the lower quartile. The upper quartile's greater milk price is argued to be achieved through contract negotiations and higher milk quality, and this accounts for 0·12 of the variation in net margin performance. The average economic return to the sample of dairy enterprises in this survey year was less than ￡6000/farm/yr. However, the most profitable quartile returned an average economic return of approximately ￡50?000 per farm/yr. Structural change in the UK dairy sector is likely to continue with the least profitable and typically smaller dairy enterprises being replaced by a smaller number of expanding dairy production units.     

Grid soil sampling adoption and abandonment in cotton production

Technology adoption in precision agriculture has received considerable attention, while abandonment has received little. Survey data are now available to evaluate adoption and abandonment decisions. Understanding the factors motivating technology adoption and abandonment has implications for educational efforts directed toward improving the efficiency of production inputs and for research and development to improve the value of precision agriculture technologies. The objective of this research was to identify factors motivating the adoption and abandonment of grid soil sampling in precision cotton production. These decisions were evaluated assuming a random utility model. Data were obtained from a 2005 survey of cotton producers in 11 Southeastern states in the USA. Results from limited dependent variable regressions indicate that younger producers who farmed more cotton area, owned more of their cropland, planted larger amounts of non-cotton area, used a computer for farm management and used a Personal Digital Assistant (PDA) in the field were more likely to adopt grid soil sampling for cotton precision farming. Results also suggest that producers with more cotton area who owned livestock and adopted management zone soil sampling were more likely to abandon grid soil sampling, while those who used a PDA in the field, used grid soil sampling for more years and followed up grid soil sampling with variable-rate fertilizer application were less likely to abandon grid soil sampling for cotton production.     

Economics of Variable Rate Lime in Indiana

In Indiana, variable rate application (VRA) of lime is often considered a good place to start site-specific management (SSM). This is because soil pH is one of the most variable of manageable soil characteristics in the state, the availability of essential nutrients is closely related to soil pH, and because spreaders can be retrofitted relatively inexpensively to do VRA. The objective of this study is to evaluate the profitability of VRA for lime as a stand-alone activity. The methodology involves a spreadsheet model using corn and soybean pH response functions estimated with small plot data. The overall results indicate increased annual returns to corn and soybean production with site-specific pH management strategies. On average, SSM with agronomic recommendations provides an increased annual return of $7.24 per hectare (ha) (+1.78%). SSM with the economic decision rule provides an average increase in annual return of $19.55 ha^–1 (+4.82%). Information strategy, which uses site-specific information to determine the economically optimal uniform rate of lime, provides an average increase in annual return of $14.38 ha^–1 (+3.54%).     

Mapping Grain Sorghum Yield Variability Using Airborne Digital Videography

Mapping crop yield variability is one important aspect of precision agriculture. Combine-mounted yield monitors are becoming widely available for measuring and mapping yields for different crops. This study was designed to assess airborne digital videography as a tool for mapping grain sorghum yields for precision farming. Color-infrared (CIR) imagery was acquired with a three-camera digital video imaging system from two grain sorghum fields in south Texas over the 1995 and 1996 growing seasons. The multispectral video data obtained during the bloom to soft dough stages of plant development were related to hand-harvested grain yields at sampling sites determined from unsupervised image classification maps of the two fields. Significant correlations were found between grain yields and the red band, the green band, and the normalized difference vegetation index (NDVI). Regression equations were developed to describe the relations between grain yields and each of the three significant spectral variables using an exponential model and two segmented models. Multiple linear regression equations were also determined to relate grain yields to the three bands and NDVI. These equations were then used to estimate grain yields at each video image pixel within each field and to generate grain yield maps. Comparisons of the estimated average yields from the regression equations with the actual yields indicated that yield estimation errors from the equations ranged from 0.0 to 10.0% in 1995 and from 0.2 to 7.3% in 1996 for field 1, and from 4.0 to 11.2% in 1995 and 6.3 to 12.5% in 1996 for field 2. Although the equations developed for one field in a given year may not apply to the same field in any other year, the practical value of these relationships is for mapping within-field grain yield variations. The results from this study showed that airborne digital videography, combined with ground sampling, regression analysis, and image processing, could be a useful approach for mapping spatial crop yield variability within fields.