Most of the summer forage crops are ensiled to feed livestock during winter, which is a common practice, especially in dairy operations. Silage crop production mainly involves intensive agronomic management to maximize tonnage and nutritional composition, while the soil health remains subtle. Soil health is defined as “the continued capacity of soil to function as a living ecosystem that sustains plants, animals and humans.”
From a sustainable agriculture perspective, integrating soil health principles into silage cropping becomes not just advisable, but imperative. As stewards of livestock and land, producers must recognize the long-term consequences of silage crop management on soil functions and productivity.
Highly productive and fast-growing summer silage crops, such as corn and forage sorghum, play a vital role in the dairy sector due to their capacity to generate huge biomass per season and high energy concentration that optimizes animal performance. However, unlike grain systems, silage crops remove nearly all aboveground biomass at harvest, leading to significant nutrient exports from the soil. The situation exacerbates when practices include frequent tillage, continuous monocropping and high fertilizer inputs, which degrade soil health over time. However, the encouraging fact is that appropriate management strategies can maintain silage yields and long-term soil health.
The following measures can provide a quick guide to assess and plan for a soil management strategy immediately following silage harvest.
Soil sampling and analysis
Silage crops extract large quantities of nutrients from the soil, often leading to a nutrient-deprived condition after harvest. For instance, a 25-ton (at 65% moisture) corn silage can remove about 90 pounds of phosphorus (P2O5 equivalent) and 200 pounds of potassium (K2O equivalent). Without adequate nutrient replenishment, repeated silage cultivation can substantially reduce crop performance and yield. Conversely, overapplying manure or fertilizers in irrigated silage production can lead to nutrient leaching, salt and phosphorus accumulation and increased ammonia emissions, all of which are critical environmental concerns. Thus, it is essential to sample soil and estimate nutrients removed by silage crops, which allows for efficient fertility management in the coming year.
Samples can be collected using push probes or a shovel at consistent depths (typically zero to 12-inch and 12- to 24-inch depths) from at least four to six randomly selected locations per acre, and composite samples should be made before sending them to a laboratory. For fields with varying slope, texture, management or cropping systems, separate composite samples are necessary to guide site-specific management. Many commercial laboratories analyze soil samples and report results to producers.
In addition to soil nutrients, periodic evaluation of soil health indicators is essential. There is no ground rule on what specific soil health indicators to prioritize; they vary based on region-specific challenges, cropping systems and available resources. Comprehensive soil health assessments should include balanced physical, chemical and biological properties to accurately evaluate soil quality and productivity. Different assessment methods, such as the Haney Soil Health Test and Cornell Soil Health Assessment, provide integrated biological, physical and chemical metrics, but it is advisable to be more region-specific and target-based for relevance, cost-effectiveness and actionable results. Some soil health indicators include wet aggregate stability, soil organic matter, carbon (C) and nitrogen (N) mineralization, microbial diversity index, soil pH, salinity and bulk density.
Assessing soil compaction
Soil compaction is the compression of soil particles, squeezing out the pore spaces that hold air and water. Compaction creates a dense soil layer that 1) restricts root penetration, 2) reduces the ability of roots to access soil water and nutrients, 3) impedes water movement, leading to increased runoff risks and 4) reduces crop performance and productivity. During harvest operations, frequent movements of heavy farm implements such as silage choppers and trucks may contribute to surface and subsoil compaction. If the soil is slick and easily forms a ribbon, it is probably too wet for heavy traffic. In addition, silage crops are ideally harvested when the crop moisture content is about 65% to 70% to enhance storage efficiency, but harvest operations under moist soil conditions may exacerbate the compaction issues.
Soil compaction can easily be assessed by taking a spade and digging in both the traffic lanes and non-traffic areas, and by feeling the difference, or tracking the hardpan layer. Soil penetrometers can also be used to get quantitative data on soil compaction at different field spots. The assessment can guide tillage decisions and cover crop selection, for example, using subsoiler tillage to till the field facing subsurface compaction and planting deep-rooted cover crops to minimize compaction issues. Controlled traffic farming can be a feasible strategy where permanent lanes for machinery are established to limit soil compaction to designated zones. Also, adjusting tire size and inflation pressure to match implement weight can mitigate the severity and depth of soil compaction.
Planting suitable cover crops
Cover cropping can be a viable strategy to integrate in silage cropping systems, considering its potential to improve soil organic matter storage, enhance nutrient cycling, suppress weeds and pests, and reduce soil erosion. Cover crops can scavenge residual nutrients and prevent their loss to the environment. Large-scale dairy operations can benefit from cover cropping by utilizing crops for livestock grazing or as greenchop. However, grazing requires careful timing and stocking to avoid compaction or excessive residue removal. Planting small-grain forages such as oat and triticale in the fall can provide supplemental forages while diversifying root structures, breaking pest cycles and improving nutrient use efficiency.
Planting cover crops immediately after summer silage crop harvest can be challenging, considering the limited growing window to obtain greater biomass and establishment before the harsh winter. Interseeding cover crops in the early stages of silage crop growth period may alleviate the short growing season of winter cover crops. Cover crop species selection is mainly determined based on the primary objective (e.g., radish for reducing compaction, annual ryegrass for scavenging residual nitrogen). It is also advisable to include cover crop species in mixtures from different functional groups (e.g., grasses, brassicas, legumes) to benefit from the complementarity of component species.
Applying manure or compost
Manure (solid or slurry) is a valuable soil amendment resource for maintaining organic matter content and recycling nutrients in silage systems. Soil organic matter is crucial to aggregate stability, nutrient retention and microbial habitat and diversity. Manure also has the potential to replenish nutrients for the subsequent crops, support microbial growth, improve soil physical conditions and, most importantly, reduce reliance on synthetic fertilizers. Manure also provides carbon-rich materials to sustain microbial diversity, critical to soil functions and processes. Therefore, manure application in silage cropping promotes sustainable management by closing nutrient loops in integrated crop-livestock systems.
It is essential to analyze the nutrient composition in manure or compost before application to maintain nutrient balance and improve efficiency. Nutrient losses associated with manure application, including ammonia emissions, leaching or runoff, should be carefully considered. For summer annual silage crops, fall manure applications followed by timely soil incorporation, or avoiding spreading manure on saturated or frozen ground, can minimize nutrient losses. In addition, manure may accumulate salt concentrations and increase phosphorus levels in soil; thus, proper calibrations should be made before applying to avoid nutrient excess and runoff. Compared to manure, compost can reduce pathogen risk and stabilize nutrient levels.
Conclusions
It is worth noting what worked well and what did not. Future adjustments in management aspects, such as harvesting time, equipment choice, tillage activity and soil amendments, can be made through strategic planning. Soil health practices often involve upfront costs or learning curves, e.g., cover crop seeds and establishment, new equipment for reduced tillage or changes in nutrient management. However, long-term benefits such as reduced input needs, improved soil productivity, managed field traffic and yield stability may offset many of these costs.
As the agricultural sector adapts to the dual challenges of feeding a growing population and sustaining natural resources, soil health must be a central consideration, not an afterthought, in silage cropping systems. Protecting soil is not an expense; it is an investment in the future productivity and resilience of the farm.
