What is Silage, and How to Produce it

Maize (Corn)

Nikolaos Barkolias

MSc Agronomist & Oenologist

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Silage is a type of forage produced by fermenting plant matter under anaerobic conditions until it’s acidified. It is used to feed domestic animals such as sheep, goats, and pigs, but it’s mainly widespread in cattle. A wide variety of plants can be used to produce silage. Some examples are sorghum, alfalfa, other legumes, grains, and corn. Unlike corn kernels (given whole or in flour and mixes), silage is produced from the whole corn plant (leaves, stems). Silage is considered a nutritious roughage for domestic animals and is particularly attractive to them due to the aroma produced during fermentation. Studies show that relatively to other forages, silage is either superior or does not negatively affect the amount of production (1, 2). From the growers’ point of view, the production of silage presents some opportunities, since the yield exceeds 60 tons per hectare (24.3 tons/acre), giving the producer a price about the same or higher in some cases than the production of corn seed. In addition, the plot is occupied less time, giving the option of multi-cropping (cultivation of more than 1 crop per growing season. Additionally, less time for the plants to grow means less irrigation and lower production costs while decreasing the risk of potential damage and losses (e.g., wild boars, wind storms, hail). This article will focus on silage production and not silage-based animal ration formulation.

As can be understood, to grow maize for silage requires some adjustments to be made in the cultivation practices compared to the ones applied for grain production. Seeding density, suitable hybrid variety, fertilization, irrigation, time, and method of harvesting are some parameters to consider.

Which are the best Corn Hybrids and Varieties for silage

Historically, corn breeders aimed to increase grain yield per unit area. It is recommended to choose seeds with a high final grain yield. However, research indicates that quality is more related to the digestibility of the cell walls of the stem than to the ratio of grain to fodder (8). Today, if we look in the catalogs of major seed companies, we will see that many seeds are listed as suitable for silage cultivation without being exclusively intended for silage.

Sowing & Plant density

The proper sowing density, and by extension, the plant density, will affect the volume of production and the desirable quantity and size of the ear. Generally, the seeding density is usually increased by 7,5-20% compared to the crop for grain. A density of up to 8-9 plants per m2 ( 6,6-7,5  plants per yd2) is considered ideal. Higher densities decrease forage quality by reducing protein and increasing fiber (9, 10). In many cases, maize is sown at 60-76 cm row spacing and 15-19 cm on the row. At the same time, there is also the option of double rows with a distance of about 30 cm within the row and 96 cm between the rows, which also seems efficient (10).

Environmental requirements for growing silage

Environmental factors affect the yield, the length of the growing season as well as the quality of the final product. Corn can be grown both with and without irrigation. In most regions, to produce silage and achieve high yields, farmers choose to irrigate. Finally, the temperature is an important environmental factor, with the ideal for maize growth to be 35 °C (95 °F) (4).

Fertilization needs for growing corn for silage

A silage crop removes more nutrients from the field since the whole plant is harvested, and there is no return of these to the soil from crop residues such as stalks. Generally, the Nitrogen requirements for silage corn production are 200-300 kg nitrogen per hectare (178-268 lb/acre) (7, 10). This quantity can vary, and is affected by the intensity of cultivation of the plot (sowing density), the previous cultivation, and its fertility. In addition, the crop needs Phosphorus (P) in the amount of 30-40 kg per hectare (27-36 lb/acre) and up to 160 kg of Potassium (K) per hectare (143 lb/acre) (10). In any case, over-fertilization should be avoided as it can lead to excess nitrate and potassium concentrations in the silage, leading to nutritional disorders in dairy cows during the dry season (7).

The Cutting stage

Cutting the stems is crucial as it affects both the amount of production (yield) and the quality-digestibility (quality and quantity) of the product. Research has shown that late cuttings yield fewer non-structural carbohydrates and increased fiber (3). An ideal Dry Matter (DM) content is between 33-36% (5, 6). Estimating maturity from grain observations, some suggest harvesting when the milk line of the grain is between ⅓ and ½, while others between ½ and ⅔. The milk line is the “dividing line” in the seed between the starchy outer part and the softer milky center.

Forage harvesting

The cutting for harvesting the stems is done 10 cm from the ground. Increasing the cutting height only slightly increases the quality of the silage with a countermeasure decrease in the quantity. Most farmers harvest exclusively with machines (agricultural tractors and forage harvesters). In contrast, in small-scale farms with higher availability of workers, harvesting is done by hand and using only small devices, mainly for shredding.

The ensilage process

The shredded maize enters the silo, which will be compressed and covered to start the silage process. Silage can proceed in large piles where agricultural tractors repeatedly trample the forage, in large tonne capacity bags, plastic containers, or even in small sacks. In all cases, ensilage is based on achieving anaerobic conditions. After closing, the aerobic bacteria begin consuming oxygen, producing carbon dioxide and heat. With the depletion of oxygen, the proliferation of anaerobic bacteria of the genus Lactobacillus begins, which produce lactic acid that acts as a preservative due to the drop in pH and gives a pleasant aroma and taste to the product. Producers often inoculate the product with formulations to protect it from fungal action and mold growth. Inoculants usually contain strains of the species L. buchneriL. caseiL. plantarumL. lactisEnterococcus sp., and Pediococcus sp.. Apart from the inoculants, molasses (sugars), urea or ammonia (nitrogenous compounds in cases of low protein content), and calcium can be added. The finished product will be ready in 4-6 weeks. In general, silage contains 40-60% water (decreases as cutting delays), fibrous substances (NDF) 41-52% in Dry Matter, and the most indigestible ADF at 24-32%, while proteins at 6- 8%. These fibers decrease as the seed develops. The pH ranges between 3,7-4,1 (9, 10, 11).

References 

1 https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-2494.1962.tb00284.x

2 https://www.sciencedirect.com/science/article/pii/S0022030299755402

3 https://www.sciencedirect.com/science/article/pii/0377840186900039

4 https://www.sciencedirect.com/science/article/pii/0377840195008853

5 https://www.sciencedirect.com/science/article/pii/S0022030265884089

6 https://www.sciencedirect.com/science/article/pii/S0022030268872820

7 https://acsess.onlinelibrary.wiley.com/doi/abs/10.2134/agronmonogr42.c12

8 https://www.sciencedirect.com/science/article/pii/0377840195008853

9 https://www.sciencedirect.com/science/article/pii/037784019290072E

10 https://www.tandfonline.com/doi/abs/10.1080/00103628509367587?casa_token=joAB2fHn0ekAAAAA:4UU878hJjiDo6Fv0CqwKk5F76mAJuM3EAN07dAqtLUNlRNefNM3_nC5vns0bek4ewpNbc9wIvT0

11 https://www.sciencedirect.com/science/article/pii/S0022030297762027

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