Web-based Adapt-N case study on N use
Since the late planted corn’s growing season was cut short by over a month, the yield goals were lowered from the earlier planted corn (from 230-to-250 down to 190-to-210 bu/ac). The Adapt-N tool was run through the Web portal every five days starting on June 6, 2011 until the crop was determined to be too high for possible sidedress N application.
Adapt-N provided many outputs, but for this case study we focus on recommended sidedress N rates and levels of excess N. Planting date was the largest factor affecting N rate recommendations: The average recommended rate (i.e., the N deficit in the soil-crop system) for the Aprilplanted corn was around 31 lbs/acre, even though 160- to-200 lbs/ac had already been applied (Figure 2). This is explained by post-planting losses as a result of high rainfall in May.
click image to zoomFigure 2: N recommendations for early (before May 1) and late planted (after June 1) corn. Each point on the graph represents an individual field. Conversely, the Adapt-N tool estimated excesses averaging 100 lbs/ac for the fields that were planted in June (Figure 2; note that excesses are indicated by negative N rate recommendations). In these cases, no post-planting losses were experienced due to dry weather conditions in June and July, and additionally the yield potential was lower due to late planting. Figure 2 indicates that the N rate recommendations modestly decreased (and N excesses increased) over time as June and July weather experienced lack of rainfall, because the probability of post-application N losses declined as crop growth progressed.
Organic matter ranged widely on the farm and affected Adapt-N recommendations: As organic matter increased, the recommended N rate decreased for the early planted corn, and excesses increased for the late planted corn (Fig. 3). click image to zoomFigure 3. N recommendations as affected by soil organic matter content, soil type and planting period. Each point on the graph represents an individual field.
In this case study, the Adapt-N tool incorporated multiple factors – especially those associated with weather – into the development of N management recommendations. The main benefit for this farm in 2011 would be the accounting for the effect of early vs. late planted fields and variable soil organic matter contents if most N were applied as sidedress instead of pre-plant. The early-planted corn required additional N to make up for post-planting losses from wet May weather, which would otherwise result in yield losses from N deficiencies.