Population
Childs targets 44,000 plants per acre, and the high density is undoubtedly a key component of high yields. He suggests that his ear size is roughly 800 kernels, so at 44,000 ppa you can calculate yields of about 391 bu/acre. If you do the math and drop that population to 30,000 ppa, yields would be a mere 267 bu/ac. My calculations assume this large ear size is fixed and would not expand with lower populations: this would not necessarily be the case, but it serves to illustrate that a significant portion of top-end yield comes from high density.

Getting your density correct requires an appreciation of the fact that high density may result in high yield and high stress. Getting the population right means getting it right for the hybrid you are growing and getting it right for the yield potential of the field. Some hybrids will simply not respond to high densities, and some low productivity soils already pose enough stress on the plant that higher populations are likely only to compound the situation.

I found it hard to walk away from Child’s presentation without feeling that boosting populations by 4,000 seeds per acre on high yield potential fields, using a hybrid that has had some high population success, was the simplest $8/acre experiment to push towards higher yields.

Depth of Tillage
Mr. Childs seemed quite concerned over soil compaction. This was reflected in his efforts to limit the number of passes over the field, in the low inflation pressures in his combine tires (15 psi), and perhaps most significantly in his use of a mini-moldboard plow with a plowing depth of 14 inches.

The mini-moldboard plow is not unlike the modified moldboard plow of years back, where enough of the moldboard was removed to prevent the complete inversion of the furrow, thus leaving a significant amount of surface residue while still maintaining the advantages of the moldboard action.

I find very little evidence in Ontario (or in the research in general) to support the concept that deep tillage would promote higher yields, except perhaps for the soils with high clay contents. Especially concerning would be the idea of using a plow (mini-moldboard or not) at depths of 14” if your topsoil stopped at 6”. Can there be any benefit of mixing sub-soil in with the topsoil material? I doubt it, and hence our anti-compaction efforts are perhaps better focused on tools like the in-row rippers or disk-rippers where we can loosen compaction without mixing soil horizons.

In Ontario, we need to do a better job of understanding the level of consolidation within our soils, and the extent to which it limits yields. Proper testing of deep tillage systems and the corn plant response is still required under our conditions.

P and K Levels
The most startling numbers presented by Childs were the soil test levels for phosphorous and potassium from his record-breaking yield areas. Here the P levels were 3 or 4 times what we might consider to be high in Ontario, but the K levels were a full 10-fold greater than what we might anticipate. And these P and K levels were high not just in the top six inches, but clear down to the two-foot depth mark. Childs reports having built these very high nutrient levels over years of manure and fertilizer applications, and now applies fairly modest rates of either phosphorous or potassium through the planter. Certainly the idea of deep tillage may have little merit from a strict soil density perspective, but if you are going to build and incorporate this sort of high fertility to 24 inches deep, you may have no other choice but to do deep, mixing tillage on an annual basis. Indeed there is some evidence to suggest that elevated P and K fairly deep into the soil profile may be a common element in many of the ultra-high yield scenarios.

If your farm has topsoil that stops at eight inches, is there any value in trying to build very high soil fertility levels in the sub-soil? That is, if you have very little organic matter, exchange capacity, or available water-holding capacity, is there any yield to be gained by elevating P and K levels in this sub-soil? Our research approach in this area has essentially taken strip tillage equipment and banded K, or in some cases P and K, in the fall while doing strip tillage. These bands have usually been 5-8 inches deep, and so far corn yields on these research plots have not been enhanced to any great extent. In nearly all cases, these have been single applications in the fall, with yields monitored the following season. Year 2 of any research, for rotation reasons, would mean moving to a new field and re-evaluating the approach. More recent efforts will look at banding the fertilizer deep, every fall, in a corn-soy rotation in order to raise P & K levels over time.

Late Season Plant Health
Dr. Thys Tollenaar, Department of Plant Agriculture, University of Guelph, has conducted numerous experiments examining the photosynthetic rates during the grain-filling period. His work has shown significantly lower rates when comparing old hybrids to new hybrids and when measuring corn plants that have been exposed to a very cool overnight period. His work points to the idea that situations that minimize stress and provide opportunity for high yield will most certainly have high photosynthetic rates which are sustained over a vast portion of the period from silking to black layer. Often these high photosynthetic rates and their persistence are associated with excellent late season plant health or “stay green”. So at the point in the presentation where Mr. Childs shows a photo of a corn plant that is 10 days away from black layering, and it looks as green as Ontario corn in July, bells start going off! Big yields can’t be produced if the plant doesn’t continue to supply carbohydrate to meet the demands of the filling ear. No doubt many factors contribute to this late season plant health, but some may focus on the nitrogen management side of the production system.

Table 1 outlines the nitrogen applications used on the Childs farm. A few growers have approached me to discuss the idea of the late season sidedressing when the corn is 5’ tall. This is not a foliar application, but drop pipes that run the UAN on to the soil surface. My fear is that the efficiency of this application may be terribly dependent on getting a decent rainfall before the corn gets too far along into the grain-filling period. Some investigations into this approach are likely to continue. Growers should be advised to monitor the late season plant health of their corn while keeping in mind a number of issues (i.e., hybrid selection, planting date, disease pressure, etc.) and not focus solely on nitrogen as a way to improve the colour of their corn in early September.

If your goal is to produce corn with a low cost per bushel and a small environmental footprint, there are some things that should spark your interest and some things that you should question from Francis Childs’ approach. However, his commitment to a positive attitude and his willingness to change are sound advice for all those seeking to become more efficient.

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