What should we expect with drought stressed corn silage? Well, a lower yield. But beyond this obvious smart alec comment, there are a few other things that occur and the impact on the nutritive value and ensiling ability depends on the growth stage of the corn while experiencing drought and if heat stress simultaneously occurred.

Drought Timing

During the vegetative period a drought tends to reduce total growth. If combined with heat stress (over 95 degrees F) drought will accelerate plant maturity, reducing the space between internodes at the time of tasseling, leaving us with a short plant and reduced tonnage. Cob size is likely also reduced. If the timing of the dry period is during pollination we may have an adequate amount of forage, however, we are left with reduced grain yields due to poor cob fill. This means fewer kernels and/or lower test weights.

Impact on Nutrient Content & Digestibility

It is difficult to make wide sweeping statements as to how the nutrient content changes with drought since timing needs to be taken into account as well as other conflicting influences occurring simultaneously. Let’s start with NDF (fiber) digestibility (NDFd). Higher NDFd translates to greater energy and drought stress tends to increase NDFd. This is because the higher lignified internode area between leaves is reduced compared to non-drought stressed corn. Heat stress, however decreases NDFd since it tends to encourage lignification. Considering the grain portion, poor pollination reduces kernel formation and subsequent starch content. With lower starch, the NDF concentration will become a higher percent of the plant. Starch digestibility, like NDFd, does tend to be greater in drought. 

Protein concentration in the grain may be less because of fewer kernels, or it may be greater if there are still kernels, but a low test weight. Within the vegetative portion of the plant, crude protein concentration may be higher due to earlier harvest or a build up of nitrates in the lower portion of the stalk. True protein may be the same or lower due to a larger portion of the crude protein being a non-protein nitrogen source such as the nitrate. 

Impact on Silage Fermentation

Starch and sugar content, protein content, NDF digestibility, moisture and natural plant microflora are all factors impacting fermentation and are modified under drought and heat stress. We briefly discussed starch, protein and NDF above, but moisture plays a big role in fermentation. Drought plus heat dries the plant quickly and the moisture needed for a good ensiling may not be present if harvest is delayed. Bright sun shine with heat during harvest also can reduce the natural microflora on the plant tissue and these initiate the fermentation process. This becomes a good reason to consider using an inoculant under these conditions.

As mentioned the timing of the drought can modify grain yield and this in turn reduces the fermentable carbohydrate (starch). If kernel formation occurs, but reduced starch (test weight) is the issue, higher crude protein levels can buffer the pH drop after fermentation begins. This pH drop might already be compromised from reduced starch and a lack of or reduced pH drop ultimately makes preservation more difficult. Thankfully, NDF digestibility seems to improve in a drought stressed plant and this can offset the decreased fermentable carbohydrate levels due to less starch (test weight or kernel numbers) in the grain. The rate at which this digestible NDF ferments may be slower than starch, thus extending the ensiling period needed to reach a bunk-stable end product. 

The Undesirables

Nitrates often come to mind with drought stressed plants and this issue tends to be most prevalent in well fertilized plants after a rain event. The nitrate is especially problematic with pregnant animals, but in the ensiling process it can promote the release of silo gas (NO₂) which is a killer to both man and beast.

Mycotoxins happen and they are present even during drought. Aflatoxin is a common mycotoxin during drought and heat events. The mycotoxin is often discussed in the context of grain, but in reality, the forage component tends to have higher concentrations when a mycotoxin like aflatoxin is present.  

Poor tip fill, a typical characteristic of drought stress during pollination – G. Ferreira 2016

Reduced cob size (on left) due to weed pressure induced drought

July provided some much needed drought relief to alfalfa acres across the state. Pastures benefited as well, but when rain arrived, the dry areas with restricted pasture growth already had cool season grasses headed out, and lost significant forage production typically provided in the spring flush.

Therefore, multiple producers are looking at any options that might stretch their pastures to graze a few more days rather than reducing numbers or buying more hay. There are strategies to help achieve goals, but each has significant tradeoffs. The focus of each is to reduce forage needs. This means maintaining fewer animals on the forage or supplementing another feed source.

1.     Early weaning. Calves at side consume forage along with the dam and put additional nutritional demands on the lactating dam. A multi-year study done in North Dakota found that weaning 90 days earlier (in August vs November with a mid-April average calving date) cut forage disappearance by 36%. This additional forage can allow drought stricken producers to extend the cow herd’s grazing season and reduce hay feeding days. Another advantage, is if summer feed has been limited and cows need to add condition before calving, by ceasing lactation, her nutrient demands are significantly reduced and it becomes easier to regain condition. However, weaned calves still need a high-quality feed, and not all facilities are suited to lightweight calves. Target market window should also be considered. Drawbacks of early weaning include a more intensive health and nutrition protocol.

2.     Preg check early: The forage savings potential on this is solely driven by marketing open cows earlier than normal to get them off the pasture and feed bill. Cows marketed earlier in the fall traditionally bring a better price as well, when sold before the market is saturated. Each mature, 1400 lb female identified as open and marketed 15 days earlier, saves ~500 lbs of forage on a dry matter basis. This is also an opportunity to identify females that do not fit your herd goals, and the option to market them as bred females.

3.     Supplement concentrate feeds: This is trading off sourcing one feed for another, but depending on situations, supplementing on pasture and gaining a few non-hay days may be preferable. It’s extremely important to note – 1 lbs supplement DOES NOT equate to 1 lb of pasture forage saved. A digestible fiber source (distillers, gluten, soy hulls) is better suited to displace forage in the diet compared to a starch source (corn). However, if adding protein in the diet through the supplement, initially, the dry matter intake of forage also increases. The general rule is that an energy supplement that is fed at 0.5 – 1% of BW on a dry matter basis, will reduce forage consumption. The amount of forage consumption displaced is variable, and to get an estimate of how much, a nutritionist will need more information. The energy supplement must be fed daily, rather than every other day to impact forage consumption. Pasture consumption will be offset if hay is supplemented, but again, protein will add complexity to actual pasture savings realized.

For any of these options, or others you find intriguing, reach out to your regional extension beef specialist to discuss what might best fit your unique situation. 

The month of August is a great time to analyze pastures and start planning for improvements for next year. Common questions to ask this time of year include:

• Is a legume interseeding needed?
• Are there too many weeds and undesirable grasses, and a new seeding is needed?
•  Is drinking water for livestock of adequate quality and quantity along with being adequately distributed throughout the pasture?  
• Is there sufficient forage for the grazing season, should I reduce the herd or add more pasture acres?

Take the time now, in August or early September to review pastures and write down what will be needed before next year starts the process to complete successful pasture improvements instead of forgetting and letting another year pass. Almost all pasture improvements start with soil sampling and testing, which should be completed every three to four years on pasture. Now is a great opportunity to take the samples yourself or contact an agronomist to help complete sampling. The samples can be collected, analyzed and fertilizer/lime recommendations developed before grain harvest this fall.

If interseeding legumes or no-tilling a new seeding, Iowa State recommends applying lime at least six months before seeding to allow the lime time to react with the soil since it will not be incorporated into the soil. Liming in September will allow frost-seeding in March.

When reviewing pastures, another set of eyes is helpful along with some record-keeping. NRCS staff can help with both, while bringing knowledge and experience learned from other farms. Iowa has area grazing specialists to assist the local field office and producers when requested.

Recording keeping can be completed on the Pasture Condition Scoresheet (PCS) developed by NRCS and updated in 2020. It does a great job of helping determine the current pasture condition. The PCS has 10 indicator elements that are scored from one to five points. Low scoring elements are the first ones to consider making improvements while elements scoring four or five points are lower priority. Iowa NRCS uses step-point to record 50 to 100 plant species in a pasture or paddock. This helps reduce bias on the plant community present. Legumes and weeds often appear more dominate and the step-point method shows the actual percentages present of different species. Keeping records for multiple years will help determine positive or negative movement of the pasture over time.

Pasture improvements start with planning. Analyzing and planning during the growing season works better than winter and give more time to develop a plan and budget costs before starting improvements the next year. Give NRCS a call for assistance to make improvements, no matter how large or small.

As summer is winding down, now is a good time to contact the local NRCS office for cost-share assistance for implementing improvement practices. A producer can apply for Environmental Quality Incentive Program (EQIP), Conservation Stewardship Program (CSP), or Regional Conservation Partnership Program (RCPP) at any time.

For more information about these programs, contact the local NRCS office. As the application process is continuous, sign-ups can happen at any time. At various times throughout the year, a deadline is established which allows applications to be ranked and considered for funding. A fall deadline will be set soon, and applying now starts the process and allows NRCS time to work with you to develop the best plan. The NRCS field office can help determine which program or programs may work best for you and your operation.

Perennial Vegetation Management Field Day in Marshall County on August 24

A perennial vegetation and CRP field day will be held Thursday, August 24 from 10:30 am to 12:30 pm at Wade Dooley’s farm near Albion. Dooley and DNR private lands biologists will share establishment and management tips for diversity and CRP compliance. See details in this news release.

Madison County Cattlemen’s holding a Pasture Walk September 7

Near Winterset, IA, soil health in pastures, fall pasture management, and water system infrastructure will be topics discussed in the late afternoon before an evening supper grilled by the Cattlemen. The host, Randy Gamble will share his management approach and how that has evolved over the years. The program will be partly held inside, and part outside where the host has a rotational grazing system, and has utilized EQIP and various conservation programs to optimize use of each acre on the farm. There is no cost to attend thanks to sponsors. Registration is requested by September 5. See details in this NRCS news release.

Iowa Beef Center’s 2023 Fencing & Grazing Clinic is September 14

The daylong event will be held near Baldwin, IA, with topics including building your paddocks, new tools in fencing, grazing leases and contracts, and managing heavy use areas around water. A walk through the hosts pasture with rotational grazing implemented as well as a producer panel discussing their experiences designing a rotational grazing system will be included. A great group of sponsors means no charge to attend. Registration is requested by September 11. See details in this IBC news release.

Education Funds Available

Planning a forage-related meeting and looking for sponsorship dollars to offset meeting expenses? The Iowa Forage & Grassland Council provides Education Grants Program which is designed to assist with funding forage education activities in Iowa including forage field days, informational meetings, and pasture walks. Learn more about the grant on the IFGC website.