Influence of Plant Health on Corn Silage Yield and Quality

This trial supports the understanding that healthy corn plants may have modestly lower %NDFD30 mid-growing season compared to more stressed plants. However, plants that are healthier mid-season are more resilient, thus have much more sustainable %NDFD30 as harvest approaches – particularly when experiencing late season stress.

Evaluation of 141 samples (Pioneer, n=95 & all competitors, n=46) within an approximately 20 mile radius over two years (2016-17) suggests hybrid genetic background strongly impacts differences in plant health and relative dry down rates. WPCS%DM at varying kernel maturities (i.e. dent, ¼, ½, ¾ milk lines) showed negligible average differences among all hybrids tested following the low stress August 2016. However, with a more stressful August 2017 (cool & droughty, followed by hot & windy), WPCS of Pioneer^® brand hybrids were on average 1-2%DM lower at the same kernel maturity than the average of all competitor hybrids (data not shown). Additionally, the Pioneer^® brand hybrids displayed more staygreen at the same kernel maturity when under stressful pre-harvest conditions.

The earlier mentioned study of %NDFD30 from R2 through R6 (Figure 1) also documented genetic differences under late season stress. The five hybrids observed represent Pioneer TS tolerance hybrid characterization scores of 4, 5, 6 & 7 (higher is better). A fifth hybrid of a competitive seed brand with unknown TS score was observed having the lowest TS tolerance of the group (Figure 2).

The three hybrid products with more favorable TS tolerance scores (5, 6 & 7) decreased in %NDFD30 from dent to ½ milk line at the same rate at all locations (most stressful and least stressful). The hybrid with the lowest TS tolerance experienced a %NDFD30 decrease similar to other hybrids at the healthiest location; however, it lost fiber digestibility more than 2X faster when under disease pressure at the least healthy location (Figure 3). In this trial, hybrid effect on plant health appears to have a greater influence on harvested %NDFD30, while hybrid differences have a minimal impact on %NDFD30. In other words, a hybrid ranking for %NDFD30 can change greatly from field to field, one harvest date versus an alternate harvest date, or one year compared to another year. 

While research on the effects of fungicides is common for grain corn, data is limited regarding fungicide use on corn intended for silage. Even fewer trials consider that yield and quality values change through the harvest window. This consideration is especially important as fungicide application is believed to alter the optimum harvest timing. A 2021 fungicide experiment on corn for silage was conducted explicitly to better understand the potential fungicide benefits unique to silage. Fungicide applied at silk (R1) was compared to no treatment (control) with yield and quality data collected on multiple harvest dates on a 4- or 7-day interval (Figure 4). One trial location experienced relatively low TS disease pressure (LDP), due to a highly tolerant hybrid (TS tolerance score=7) plus relatively few other stressors due to managed irrigation. A second location had very high TS disease pressure (HDP) with a less tolerant hybrid (TS tolerance score=4) under drought stress. The HDP field had optimal conditions for exponential TS disease development.

The impact of a foliar fungicide application on silage corn in HDP location is obvious to the naked eye, while fungicide application in the LDP field was indiscernible with unaided visual appraisal. Plant health imagery reveal a very subtle difference between the untreated portion of the field in LDP (Figure 4 & Figure 5).

This data suggests that fungicide could be a useful tool for managing the harvest window. Even in low disease pressure situations, a fungicide application appears to extend the acceptable harvest dry matter with little or no delay to the initiation of harvest.

There is an abundance of work analyzing the relationship of nutrient availability and uptake on grain corn yield and attributes. Recent Pioneer field trials have shed light on possible considerations in fertility management that differentiate corn intended for silage. Trials include:

1. Nitrogen side-dressed at N recommendation (rec), rec minus 50 lbs, and rec plus 50 lbs. (WI & MI 2018, n=12)
2. Nitrogen side dressing (90 lbs) combined with alternative potassium fertilization rates (0, 90, 180 lbs). (WI 2020, n=3)
3. Potassium supplementation (115 lbs) across various soil test levels (deficient to abundant). (PA 2021, n=9)
4. In-furrow (Zn, Humic acid, Fulvic acid, biological) plus 2x2 (10-34-0, 28-0-0-5, B) at-planting program. (MS 2020)

All four of these trials suggest that grain yield response plateaus with additional available nutrients, while fodder yield continues to increase. For example, treated corn in the In-furrow & 2x2 study (trial 4) demonstrated a modest 3% increase in harvested dry grain (269 vs 261 bu/A). However, plant biomass near the end of vegetative growth at tassel (VT) experienced a 21% increase with treatment (2250 vs 1884 g DM). The vegetative growth and resulting fodder biomass yield difference was visibly noticeable (Figure 7).

Based on the three trials that included silage quality analyses (trials 1, 2 & 3), the additional fiber yield may come at a slight or negligible reduction in fiber digestibility (%NDFD30) and starch content (%Starch). The trade-off in yield and fiber quality is likely associated with the previously discussed role of plant health in fiber digestibility. Thus, there may be a net zero or favorable nutritional quality effect when the corn crop is exposed to late season stressors. 

In sum, these data are not yet adequate to support increasing fertility recommendations on corn silage acres. However, the results of these four trials demonstrate that inadequate plant nutrition along with conditions limiting nutrient uptake (e.g. compaction, drought, root damage) may have more negative consequences to corn silage than corn grain. Fiber yield and digestibility are likely impacted well before the occurrence of noticeable grain yield losses due to a nutrient deficiency.

Corn plant health is indicative of silage performance in both dry matter yield and fiber quality. Healthier corn plants result in:

• Higher yields of starch, fiber, and combined whole plant tonnage
• Greater tendency to maintain fiber digestibility through the harvest window.
• More forgiving, wider harvest window offering a higher probability of timely harvest

Healthier, less stressed plants are more likely to achieve genetic potential in plant stature, grain yield, and combined whole plant dry matter yield. The taller plants also tend to be more robust, leading to additional fiber yield. The larger plants may initially have modestly lower fiber digestibility, but they are more resilient under stressful conditions. This frequently leads to an ultimate advantage in fiber quality and a more manageable harvest window. Healthier plants also afford more grain yield, thus more starch yield at the same WPCS %DM. However, the added starch dry matter yield may not always increase %Starch as a parallel increase in fodder yield may maintain a relatively constant grain to fodder ratio.

Hybrid selection, strategic fungicide use, and fertility management are readily available tools for enhancing and maintaining plant health. When applied with other good management, these practices can notably increase the probability of producing a high yielding, high feed quality corn silage for greater whole farm profitability.