Last week I sung the praises of that time period in a corn plant's life when it can change from an ugly duckling into a beautiful swan (see P&C Newsletter, No. 13, 6/16/95). Sadly, though, I must return to my usual fearmongering ways this week and discuss those situations when the ugly duckling simply grows up into an uglier duck. By this, I mean those fields that have been uneven in appearance and are becoming more so every day, especially during this current period of hot, dry weather.
Ponded, Saturated Soils. Stunted corn in those areas of fields that were subjected to ponding or simply saturated soil conditions for extensive periods is now more vivid as the rest of the field moves well into the grand growth phase. Corn does not like wet feet and the damage to developing root systems caused by oxygen-depleted soils has resulted in severe stunting. Row cultivation or the soil disturbance caused by knifing in sidedress nitrogen fertilizer can break up dense surface layers in these areas, resulting in better soil aeration.
Soil Nitrogen Loss. In many of these same 'wet holes', the potential for significant loss of soil nitrate nitrogen is great, due to either denitrification or leaching. In addition to these areas of the field being stunted, the plants will also be distinctly more yellow than other areas of the field where soil nitrogen is adequate for continued plant growth. Sidedress applications of nitrogen fertilizer will definitely encourage recovery of these areas.
If the bulk of the nitrogen fertilizer has already been applied, see Dave Mengel's recent article on estimating soil nitrogen loss (see P&C Newsletter, No. 11, 6/2/95). You may decide to apply additional nitrogen fertilizer to these 'wet holes'. Be sure to adjust your intended fertilizer application rates to account for any potential reduction in yield in these areas.
Soil Compaction. As I am sure most corn watchers are aware, soil compaction is pervasive in many fields across Indiana this year. In some fields, initial plant development was hindered by furrow sidewall compaction caused by planting in soils that were too wet. As plants near knee-high (six-leaf collar stage), their root systems extend deep enough to 'feel' the restriction caused by tillage and tire traffic compaction. Where upper soil layers have dried significantly, the above-ground symptoms of soil compaction have begun to appear this past week as air temperatures have climbed consistently to the upper 80's or lower 90's.
Above-ground symptoms of soil compaction include leaf rolling, short plants, and off-color plants. Below-ground symptoms include horizontal root growth, crooked root growth, flattened roots, and more profuse lateral root branching. Herbicide injury is also often accentuated in areas where corn roots are also being restricted by soil compaction. Remember that the severity of soil compaction in a field is usually uneven and distinct patterns of symptoms are not always evident.
Row cultivation may break up surface soil layers, but not deeper soil compaction. As with ponded areas, soil disturbance caused by knifing in sidedress nitrogen fertilizer can help shatter some of the deeper soil compaction if the soils are sufficiently dry.