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Chapter 16: Harvesting.

Key Concepts

* Harvest is the completion of the crop production cycle.

* The goal of harvest and storage systems is to maximize the harvest of the standing crop and preserve as much of the crop as possible.

* At physiological maturity, maximum accumulation of grain dry matter has occurred.

* Moisture level is a critical factor in preserving stored grain and forage.

* Forages are harvested directly by grazing or harvested as hay or silage.

* Approaches to grazing include continuous grazing and rotational grazing.

* Hay is stored aerobically, whereas silage is stored anaerobically.

* Hay often has significant field losses, whereas silage has greater storage losses.

* Types of silage include haylage, wilted silage, and direct cut.

* Corn silage is a high-energy feed stored at a moisture content of about 65%.

* Silage is stored in specialized structures, called silos, that exclude air.

Key Terms

antiquality factor

binder

black layer

bushel

combine

continuous grazing

corn silage

direct cut silage

ensiling

forage quality

harvest

harvest maturity

hay crop silage

haylage

husking

intake

lodging

milk line

nutritive value

pasture

physiological maturity

reaper

rotational grazing

sheaves

shocks

shucking

stocking rate

storage fungi

stover

swathing

wilted silage

Introduction

Harvest of the crop is the completion of the production cycle and the end of a growing season. If the harvest was plentiful, it would be a time for celebration and thanksgiving. In early agricultural societies, survival through the winter was dependent on a successful harvest. In modern production systems, harvest provides the commodity for marketing and income for the farm. In this chapter, we discuss the harvest and storage of important grain and forage crops.

Harvesting Grain Crops

As discussed in Chapter 7, crops go through several stages of development until they reach the end of a growth cycle. For most annual grain crops, the growth cycle ends in seed production. This contrasts with forage crops such as alfalfa or grasses and corn silage, where harvesting for forage often occurs before seed production. Profitable grain production must focus on maximizing grain yield and minimizing harvest and storage losses. This necessitates understanding the optimum maturity to harvest the crop.
Bushels

Grain yield is typically measured in terms of bushel per acre.
Bushel (abbreviated as bu.) is an old English term that describes a
unit of volume for measuring crop yield. A bushel is a container
18 1/2 inches (47 centimeters) in diameter by 8 inches (20
centimeters) deep (Figure 16-1). Its volume is 2150 cubic inches
(about 35,000 cubic centimeters). Today, the term bushel is still
used to express grain crop yield, but for grain marketing, bushel
is defined as the quantity of shelled grain at a specific moisture
and specific weight. For example, a bushel of corn or grain sorghum
weighs 56 pounds (25 kilograms) at 15.5% moisture; wheat weighs 60
pounds (27 kilograms) at 14% moisture; oats weigh 32 pounds (15
kilograms) at 14.5% moisture; and soybean weighs 60 pounds (27
kilograms) at 13% moisture. Other grains have specific bushel
weights (see Appendix 3).

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Physiological Maturity of Grains

Physiological maturity is a stage of development of grains when the maximum accumulation of dry matter in the seed occurs. If grain is harvested before physiological maturity, grain yield is reduced. For corn, the average grain dry matter content increases about 2% per day from pollination to physiological maturity. Corn that is subject to frost or harvested before physiological maturity is called soft corn and will have lower grain yields. Physiological maturity can be determined by measuring the moisture content of the grain or by visual indicators. Grain moisture is an indication of crop maturity (Table 16-1 and Figure 16-2).

Visual indicators help determine physiological maturity, Several crops have simple visual indicators to alert the farmer that physiological maturity is near. Some examples of visual indicators for corn, sorghum, soybean, small grains, and sunflower include the following:

* Black layer in corn and sorghum. In corn and sorghum, an abscission layer (a thin barrier of parenchyma cells) forms at the base of the kernel. This layer restricts translocation of carbohydrates to the seed. This layer is called the black layer. Corn grain moisture at physiological maturity is 30-35%.

* Milk line in corn. Another physiological indicator is the development of the milk line in corn. As the kernel approaches maturity, a line can be seen on the smooth side of the kernels. This line is called the milk line or starch layer. It is the boundary between the solid (starch) and liquid portions of the maturing endosperm. Physiological maturity of the kernel is indicated when the milk line is no longer visible, and liquid can no longer be expressed from the kernel.

* Pod color change in soybean. The loss of green color of the pods is an indicator of physiological maturity in soybean seed. The pod contributes photosynthate (sugars from photosynthesis) to the developing seed. The change of pod color to yellow and brown is associated with seed drying and shrinkage.

* Yellowing of small grain inflorescences. A significant portion of the dry matter deposited in the grain of wheat, barley, rye, and oat comes from the awns, glumes, and other modified leaves in the inflorescence. Small grains are physiologically mature when these flower parts change color from green to yellow.

* Sunflower head color. Sunflower seeds are physiologically mature when the back of the head has lost its green color and turned yellow.

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Drying of Grain before Harvest

Drying of grain in the field is a natural process designed to produce a seed that is less susceptible to attack by microorganisms and is more easily disseminated by the plant. Immediately following formation, the seed is almost 90% water. As the seed develops and accumulates nutrients, its moisture content decreases. After reaching physiological maturity, the seed continues to dry. At physiological maturity, grains are never dry enough for storage; therefore, considerable moisture loss must occur.

Water loss from drying grain occurs by whole plant transpiration and through direct evaporation from the grain surface. Water must move from the grain through seed coverings or husks. The drying rate of grain can be increased by those factors discussed in Chapter 7 that increase water loss from the plant. Increasing air temperature and airflow, and decreasing relative humidity all increase water loss and the rate of plant and seed dry down. In contrast, as seed moisture decreases during dry down, the seed loses moisture more slowly. It should be noted that because of their starch content, seeds also absorb water from rain and snow. Natural field drying is often the most economical approach to reducing the moisture content of seed.

Harvesting

The goal of harvesting is to maximize the removal of the agricultural crop from the field. This can be challenging because producers need to determine when to harvest, and because weather and soil conditions during the targeted harvest time can delay harvests. Harvest maturity is the moisture content of the crop when a combine can harvest grain with minimum field loss.

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Corn is typically harvested when grain moisture levels reach 25%. The plant is brown or tan, but the leaves are retained. Harvesting at grain moisture levels more than 25% results in grain losses because ears are not snapped off the plants as easily, and grain is not shelled off completely. At below recommended moisture levels, losses occur because the plant is more susceptible to lodging, ear drop, and seed shattering.

Soybeans are harvested directly from the field at a 13% grain moisture content to minimize field losses. At this time, the leaves have dropped from the plant and only a dried stem with pods remains. For soybean, harvesting losses of 10% or higher are not uncommon (Figure 16-3). Losses associated with harvesting are shattering of the beans and fallen stalks that cannot be picked up.

Small grains such as wheat, oats, barley, and rye can be allowed to dry standing in the field and combined directly or swathed before harvest. With swathing, the small grains are mowed, deposited on the ground, and dried in the field after they have reached physiological maturity. Swathing before harvest is an extra step but is used if there is a variation in the maturity of the crops or if a field has a significant weed problem. Immature weeds with high moisture content can block the threshing units of the combine. With cutting and drying in a swath, weeds can be fed through a combine and separated from the grain. In addition, swathing can reduce the risk of lodging of the mature crop because the process dries crops to moisture levels safe for combining. Lodging occurs when the entire plant tips over. It can be a significant problem in high-yielding small grains.

Method of Grain Harvest

All grain crops are harvested by combining. The term combine is used because this machinery combines many operations into one machine (Figure 16-4). At one time, the operations of cutting, gathering, and threshing (separating the grain from the chaff ) were separate and very labor intensive. The combine cuts and gathers the crop, threshes (shells) the grain, and uses screens and fans to clean the grain. The grain is collected in a hopper in the combine and is later mechanically transferred to transport vehicles. Grain residue (straw, leaves, and stover) is discharged from the back of the combine (Figures 16-5, 16-6, and 16-7). The residue can be scattered or placed in rows (windrows) for later pick-up and baling. Combines are complex and expensive machines. They require proper adjustment to minimize field losses and to optimize threshing efficiency. If the threshing is not adjusted, a significant amount of grain goes through the machine, or the grain can be damaged. Some farmers still use corn pickers that pick whole ears from the corn plant. These ears are often stored and fed to animals on the farm.

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Grain Harvest History: Bringing in the Sheaves

In the early days of agriculture, all crops were harvested by hand. For small grains such as wheat, farmers used the sickle, scythe, and cradle into the 1800s (see Chapter 1). The cut grain was later picked up by hand, loaded onto a wagon, and taken to a stationary thresher. Threshing was initially done manually but was later mechanized. During the early 1800s, manual harvesting was replaced by the reaper, a horse drawn cutting machine that cut labor in half. The reaper deposited cut grain on the field, and then it was manually collected. The reaper was later modified to allow operators to collect and bind the stalks of grain together. Early binders depended on operators to use some of the straw for tying the grain bundle together. Later, as automatic binders were developed, the machines used wire and binder twine made of hemp fiber to tie bundles together. The binder was another technological revolution because tied bundles of grain (sheaves) were deposited in the field. These sheaves were stacked in the field to dry and were later transported to a stationary thresher that separated the grain from the chaff. By the mid-1850s, horse pulled combines were available and were used on a limited basis.

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Historically, corn was also manually harvested. Native Americans picked the ears of grain and left the stover (that is, the remaining stalks, leaves, and husks) in the field for soil building. From colonial times into the 1800s, the corn stover was recognized as important winter livestock food and was removed from the field and stored. The grain was picked (called husking or shucking), and the remaining stover was then collected and tied into large bundles (shocks) of 10-20 plants to dry for livestock feeding. Another approach was to cut and shock whole plants in the field for drying. Then later in the field or barn, farmers husked the ears from the stover (the leaves and stalks of the corn; Figure 16-8). It took a farmer about a day to husk approximately an acre of corn that had already been shocked. As with small grains, inventors developed horse drawn binders for collecting corn shocks. Later developments included corn picking machinery that removed the whole corn ears and left the stover in the field. For many years, whole corn ears were used for livestock feeding. Because of cost, shelling (separating grain from cobs) was limited. The first field combines that harvested and shelled corn grain were not developed until the early 1900s.

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Precision Agriculture

Precision agriculture is the use of computer sensing and data
collection equipment to enhance a farmer's decision-making
capabilities. Whereas in earlier times farmers had to rely on whole
field averages for chemical application, irrigation and other
inputs; the use of GPS (global positioning systems), GIS
(geographic information systems), computers, and other sensing
equipment allows for accurate, site-specific decisions. Here's how
the various systems work.

* The GPS U.S. satellite navigation system uses signals from
several satellites to locate the specific latitude and longitude of
a position within a field. GPS enables farmers to divide their
fields into smaller, digital subunits and collect data specific for
those areas.

* GIS is a software system that stores, analyzes, and displays data
that has been collected for a specific location identifiable using
the GIS system. Data is often displayed in field maps.

* Data is collected from specific sites identified by GPS within a
field. Data includes soil characteristics based on manual soil
sampling, for example, pH and fertility; crop yields and moisture
content collected by yield mapping; and other data such as presence
of weeds and crop appearance. Data can also be collected by remote
sensing devices mounted on harvesting equipment.

Within a field, there will always be a degree of natural
variability in pH, soil composition, nutrient levels, soil
moisture, and number of weeds, that affects crop yield. With this
data, farmers can accurately manage costly inputs on a spatial
basis, thereby lowering their economic and environmental costs. For
example, through the use of soil sampling equipment and the GIS
system, farmers can create digital maps of their fields and
determine which specific subunits need more or less fertilizer
inputs. This process can save farmers money and enhance yields by
accurately distributing resources to needy areas and reducing
wasteful, average-based applications. Precision agriculture can
also reduce farmers' environmental impact by minimizing and
strategically focusing inputs and identifying areas in the farm
landscape susceptible to increased runoff, water pollution, and
contamination.

Yield monitoring using harvester mounted computers and GPS systems
has become commonplace for most crops (Figure 16-9). However,
because of the cost, variable-rate application of crop inputs at
specific sites within a field has been limited to high value crops.

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Moisture and Temperature

Several aspects of grain moisture are of concern.

* Grains are usually marketed at a certain bushel weight and moisture content. Grain that is marketed at moisture levels above the established limits are docked, that is, they receive less money per bushel.

* Grain moisture is a critical factor affecting storage. Seeds are living organisms and above-optimum storage moisture promotes seed respiration. Respiration reduces the seed's soluble carbohydrate content, releases moistures, and raises the grain's temperature. This can lead to fungi growth. Very high moisture levels and no aeration can actually lead to fermentation reactions within large storage bins.

Temperature during storage and length of storage time interact with moisture and can become a critical factor in determining storage losses. The minimum temperature for growth of storage fungi is about 40[degrees]F (4[degrees]C), with optimum temperatures from 80 to 90[degrees]F (27-32[degrees]C). Therefore, a strategy for reducing fungal growth is to store the grain at low temperatures. This often requires storage of grain in special grain bins with capacity for aeration.

Grain Storage

Grain can be sold directly following harvest or stored on-farm. Grain is stored if it is to be fed on-farm or to create a marketing advantage for the producer. Storage seldom improves grain quality, but goals should include maintaining the quality (color, purity, odor) and viability if it is to be used for planting. Grain storage facilities vary considerably depending on the length of storage and the importance of minimizing losses (Figures 16-10 and 16-11).

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Fungi, Insects, and Rodents

Damage from fungi is the most frequent cause of loss of grain during storage. Losses increase as grain moisture levels increase. Mold growth can decrease seed viability and increase discoloration, changes in seed composition, dustiness, and production of toxic compounds called mycotoxins. The fungi responsible for the reduced quality of grain are called storage fungi. These include Aspergillus spp., Penicillium spp., and several types of yeast. The spores of these organisms are found on harvest and handling equipment. They are also usually present on the walls of storage bins.

Insects such as the granary weevil (Sitophilus granaries) and the saw-tooth grain beetle (Oryzaephilus surinamensis) can cause significant losses in stored crops. They consume stored seeds and also contaminate grains with insect fragments and feces. For food grains, they cause a major sanitation problem. Rodents can be a problem in unsealed storage containers.

Drying of Grain for Storage

Moisture content of the crop at harvest is seldom at a level desirable for safe long-term storage. The most traditional approach to deal with this problem is to dry unharvested crops in the field before storage. The efficacy of this approach is greatly affected by the weather. In addition, as crops mature, there is often greater loss due to seed shattering, stalk lodging, and fungal growth on seed. Today, many high value grain crops are harvested and artificially dried.

Grains stored in piles or bins can be cooled and artificially dried using fans to move the air. Heated air can also be used to dry the grains. Alternatively, a combination of the two approaches can be used. Producers must pay for artificial drying (e.g., the costs for the propane or electricity) or allow for additional field drying. This decision is based on the cost of the energy source compared to market prices.

Harvesting Forages

Harvesting of forages occurs directly by grazing livestock or mechanically as hay or silage (Figures 16-12 and 16-13). Forages are vegetative portions of plants used for livestock feed. Forages often do not contain mature seed. Corn, sorghum, and small grain crops harvested for silage contain immature grain. The goal of all types of forage harvesting is to maximize retention of the forage nutrients growing in the field. However, field loss as high as 25% frequently occur, especially for hay crops that are slowly dried in the field. Losses in crop yield and quality during harvest is greater for forages than for grains because fragile leaves often shatter or separate from the stem during drying and harvest of the forage. Shattered leaves are lost in the field.

Forage Yield

Forage yield is measured in tons per acre. Usually, this yield includes the weight from water. Hay yield is assumed to contain 15% moisture, whereas silage is assumed to contain about 60% moisture. Forage yields can also be expressed on a dry matter (no moisture) basis. Because of variation in climate and soils, hay yields of forage crops such as alfalfa and grasses range from 2 to 7 tons/acre (5 to 16 tonnes/ hectare). Silage yields are higher than hay because of the higher moisture content and because of less dry matter loss. Corn silage yields can be as high as 30 tons/acre (67 tonnes/hectare). Forage yield is an important consideration for farmers, but forage quality is equally important.

Forage Quality

Forage feeding value is described as forage quality. The three components of forage quality are intake (how much an animal will eat), nutritive value (nutrient content), and antiquality factors. Intake is often the most limiting factor in utilization of forages. Antiquality factors include chemical toxins such as nitrates or glycosides (see Chapter 14) or morphological features such as thorns that reduce animal performance.

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When compared with grains, whole plant forages contain greater quantities of cell wall structural materials such as cellulose, hemicellulose, and lignin. They contain lower quantities of cell contents such as starch, protein, and organic acids. High cell wall content has been associated with reduced intake, digestibility, and nutrient content of forages. Nutritive value refers to the content of protein, energy, and minerals. In contrast to grains, forage feeding value is much more variable. It varies among species and is greatly affected by factors such as maturity at harvest and growth conditions (Table 16-2).

When to Harvest

Maturity of the crop at harvest has a large effect on both yield and quality. As the crop matures from vegetative (all leaves) to flowering stages, forage yield usually increases, but forage quality decreases. This is related to the decrease in leafiness with maturity and the increased proportion of the fibrous stem.

The stages of development for alfalfa, a forage legume, are as follows (Figures 16-14 and 16-15) (see Chapter 7).

* Vegetative: stems have leaves but no flowers

* Bud: stems possess flower buds but not open flowers

* Flowering: flowers are open

* Seed: flowers have pollinated and formed seeds

The stages of development for smooth bromegrass, a forage grass, are

* Vegetative: plant has only leaves

* Stem elongation: stems have elongated but no flowers have formed

* Boot stage: inflorescence is enclosed in the sheath of the last leaf

* Flowering/anthesis: grasses are pollinating

* Seed: mature seed is present

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Pastures

A pasture is grazed land on which annual and perennial forages are grown. Most pastures are enclosed by fencing. Pasturing of forages is the direct utilization of forages by grazing cattle, sheep, bison, and horses. The predominant plants used for pasture vary throughout the United States. These include perennial grasses such as Kentucky bluegrass, tall fescue, smooth bromegrass, orchard grass, ryegrass, and legumes such as alfalfa and white clover in the humid northern region; Bermuda grass in the southeast; and switchgrass, little bluestem, and buffalo grass in the drier western region. Pasturing is mostly limited to the portion of the year when pastures' plants are actively growing or are not covered by snow. In pasture systems, animals spend up to three-quarters of each day grazing. On well-maintained pastures, these animals can obtain almost all their nutrient needs. There are different types of grazing systems including continuous grazing and rotational grazing.

Continuous grazing. Animals have access to a large pasture, and they move freely about the grazing area. This approach is common in grazing of expansive rangelands in the western United States where productivity is limited by lack of rainfall or in regions where soil fertility limits grass productivity. Continuous grazing is a low management input system compared to rotational grazing. Continuously grazed pastures typically undergo seasonal cycles of overgrazing and undergrazing depending on the weather conditions.

Rotational grazing. The pasture is divided into three or more paddocks so that animal grazing is controlled and pasture plants can be rested. The average rotation period in northern United States is about 30 days. Forage is used more efficiently than in continuous grazing systems because animals are managed to utilize forages when they are at optimum nutrient levels for a specific type of livestock (Figure 16-16). In rotational grazing systems, grazing is initiated when species are vegetative before flowering and pastures are grazed to a height of 2 inches (5 centimeters) within one week at a maximum. Managed intensive grazing is another rotational grazing approach in which cattle are managed to maximize pasture utilization. Cattle are provided new pasture as frequently as every 12 hours (Figure 16-17). Rotational grazing also provides a rest period that enhances persistence of some species such as legumes. They do not persist under continuous grazing. Different types of rotational grazing include strip grazing and creep grazing. Strip grazing is an alternative approach where portable fencing is moved daily to provide a fresh supply of forage. Creep grazing is a modified rotation approach that gives calves access to the highest quality forage because they graze ahead of the cows.

Animal performance on pastures is greatly influenced by stocking rate (animal number per acre). At low stocking rates such as those often used for horses, animals can select forage with higher forage quality (Figure 16-18). Unfortunately, animals often select and overgraze the most palatable species. As the stocking rate increases, selectivity is decreased. However, the total weight gain of the livestock in the herd increases until there is too little forage to support the animals in the herd. This often happens when there are droughts in midsummer or in the late fall when climatic conditions reduce plant growth.

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Pasturing is a common practice in regions where large areas of inexpensive land are available or where animal rates of gain are not of primary importance. However, grazing of pastures is less important than stored feed on many modern beef and dairy operations. The extensive use of stored hay and silage has become commonplace to minimize animal movement on the farm and to achieve a more reliable and consistent quality forage. Animal diets are supplemented with high-energy grains.

There is growing interest in the use of rotational grazing in production of grass-fed beef as well as in organic cattle and milk enterprises. These practices, which rely heavily on nutrients grazed from pasture, are designed to produce healthy meats in a natural way.

Haymaking

When pasturing is not possible, haymaking is the traditional approach to storing forage for livestock. Alfalfa is the leading hay crop in the United States, but many other perennial legumes such as red clover and grasses such as timothy, Bermuda grass, and smooth bromegrass can also be made into hay. In many modern confinement animal production systems, stored hay is fed year-round. Hay is forage that is dried to about 15-20% moisture and stored aerobically. It is critical that hay be dry to prevent the growth of mold that causes heating and degrades the forage quality. In the haymaking process, there are four critical steps--cutting, drying, packaging, and storage.

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Cutting

The standing plants (containing about 80-90% moisture) are cut near ground level. It is frequently deposited in windrows, which are rows of cut forage fluffed to increase wind flow (Figure 16-19). A part of most modern mowing machines is a conditioning unit that crushes the stem of forages and aids drying.

Drying

The cut forage is dried in the field from one to five days depending on the temperature and sunshine. For example, in the Midwest, hay can dry in two days in mid-summer, but in the fall drying may take five days. During this time, the hay is sometimes raked or turned over. The expression making hay while the sun shines is based on the common practice of using the sun's energy to dehydrate the forage. Rain during hay drying is undesirable because it prolongs the drying process and leaches valuable nutrients. Sometime the entire hay crop can be lost if rainfall occurs for several days following cutting.

Packaging

The dried forage is baled (packaged) in the field. Hay balers are machines pulled by tractors. Baler components include pick-up fingers to lift the dried loose hay into a bale chamber that compresses the hay. Bales are then wrapped with twine and are discharged from the baler. Bales vary in size. Bales can be small rectangular packages weighing about 40-70 pounds (18-32 kilograms), large rectangular packages weighing about 500-2000 pounds (230-910 kilograms), or large round packages weighing as much as 500-2000 pounds (Figure 16-20).

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Transport and Storage

The baled hay is transported from the field and stored in a dry barn. Bales left too long in the field can be damaged by rainfall. If protected, hay retains most of its nutrients indefinitely, but vitamins are lost in storage. In a barn, hay continues to lose moisture to a moisture content of about 5%. Hay stored at greater than 20% moisture can have significant mold growth and a loss in nutrients and biomass. If hay is made at moisture content above 30%, it can undergo spontaneous combustion and burn. In addition to the loss of hay, the barn is also usually lost. Stored hay that is rewetted by rain will also mold so inside storage is desirable. Hay should not be stored in contact with the soil.

Silage

Overall, the process of cutting, baling, and storage of hay can result in as much as 20% of the forage being lost in the field and another 5% lost in storage (Figure 16-21). Some of this loss is associated with loss of sugars through respiration by the plant and fungi. Much of this loss is due to rain damage and shattering of leaves that are the fragile portion of the plant. As a result of these field losses and challenges with scheduling haymaking activities; the ensiling process was developed. Silage is high moisture forage that is stored anaerobically (without air) in a specialized storage structure called a silo. The process of making silage is called ensiling. For silage, field losses are much less because the forage is harvested at higher moisture content. This reduces field exposure to rain, field respiration, and leaf shattering. A storage structure is needed to permanently exclude air and to prevent entrance of water from rain or snow. The high moisture content of silage is important for growth of beneficial bacteria and for compaction to exclude air.

Silage is preserved for feeding by acids produced during the biological reaction of fermentation. Fermentation by specialized bacteria living on the forage changes the sugars in the plant material to lactic acid.

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Lactic acid concentration in the silage can be from 5% to 10%. Lactic acid reduces the pH to 4.5 or below. This low pH preserves the forage and inhibits growth of fungi, bacteria, and yeasts. It permanently maintains the forage. During the ensiling process, it is important that the forage material be compacted and that the air be rapidly excluded. Exposure to air in the early stages of ensiling delays fermentation and can result in losses of energy and dry matter of the forage. Exposure of silage to air results in fungal growth.

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Two Types of Silage

There are two main types of silage: corn silage and hay crop silage. Corn silage is made from finely chopped (1/2-inch or 1/3-centimeter in length) whole corn plants that are mechanically harvested. The whole corn plant is immature and typically has a moisture content of 65%, whereas the grain is about 30% moisture. Corn silage is a high-energy feed. Relative to hay crop silage, corn silage has a higher level of energy that promotes fermentation.

Hay crop silage is made from alfalfa and grasses like smooth bromegrass that can also be made into hay. These are lower in energy and higher in fiber and protein than corn silage. Small grains like wheat and barely can also be made into silage if harvested before mature. The three types of hay crop silage based on moisture content at ensiling are

* Direct cut silage (80-85% moisture) is cut and chopped from the field, usually in the same day. The high moisture content can interfere with fermentation.

* Wilted silage (60-75% moisture) is made much like hay with the cut forage dried in windrows to the target moisture and then mechanically picked up and chopped. Field drying time can be from four to eight hours. This is the most poplar type of silage.

* Haylage (40-60% moisture) is dried in the field longer than wilted silage. Haylage contains less moisture than wilted silage and is difficult to pack and exclude air. It is made most often in tower silos (Figure 16-22). Haylage ferments less than wilted or direct cut silage.

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Advantages and Disadvantages of Silage

Preservation of high moisture forage as silage has several advantages compared to hay. These include (1) less exposure to the weather during field drying, (2) more nutrients preserved due to reduced field loss, (3) more opportunity for mechanized handling and feeding and therefore fewer labor needs, and (4) potential for long-term preservation.

The primary limitation of ensiling relates to the cost of machinery and silos. However, lower cost approaches to ensiling have been developed that substitute labor for mechanical costs. These include:

* Balage--individual bags of baled silage wrapped in plastic (Figure 16-23)

* Silobags--large bags of silage

* Compacted piles and bunkers covered with plastic

Review Questions

1. What is the main goal of harvest and storage systems?

2. Why is it important to determine when physiological maturity has been reached?

3. Why is additional dry down of grain often required before storage?

4. What can happen to grains if they are stored at greater than recommended moisture levels?

5. Describe the different ways in which forages are harvested.

6. Distinguish between continuous and rotational grazing.

7. What are the main differences between hay and silage?

8. Identify crops that are made into hay and silage.

9. What happens to hay if it is stored at a moisture content that is higher than 20%?

10. How is silage stored?

Critical Thinking

1. In your state, when are the important crops that are harvested?

2. Do animals need to be pastured, or should they be confined and fed hay or silage?

3. Many inventors have made significant advances in agricultural machinery. These include Cyrus McCormick, Obed Hussey, John Deere, James Oliver, and Eli Whitney. For two inventors, identify their invention(s) that advanced agriculture. In addition, indicate the time in which they lived, where they lived, and where their inventions were used.

References

Acquaah, G. (2005). Principles of crop production (2nd ed.). Upper Saddle River, NJ: Prentice-Hall, Inc.

Barnes, R. F., Nelson, C. J., Collins, M., & Moore, K. J. (Eds.). (2003). Forages: An introduction to grassland agriculture, Volume I (6th ed.). Ames, IA: Iowa State Press.

Board on Agriculture. (2001). Nutrient requirements of dairy cattle (7th ed.). Washington, DC: Nation Academy Press.

Freeman, J. E. (1980). Quality preservation during harvesting, conditioning, and storage of grains and oilseeds. Madison, WI: American Society of Agronomy, Crop Science Society of America.

Harper, D. (2001). Changing works: Visions of a lost agriculture. Chicago: The University of Chicago Press.

Janick, J., Schery, R. W., Woods, F. W., & Ruttan, V. W. (1981). Plant science: an introduction to world crops (3rd ed.). San Francisco: W.H. Freeman and Company.

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University of Minnesota (1999). Minnesota soybean field book. St. Paul, MN: University of Minnesota Extension Service.
Table 16-1
Moisture content at physiological maturity, harvest, market, and for
safe storage. Long-term storage is for one year or more. These values
are for the northern states; moisture values for the South are lower.

          Physiological                      Long-term
Crop        maturity      Harvest   Market    storage

Corn          30-35        25        15.5       13
Wheat         30-35        15-18     14         13
Barley        30-40        10-18     13.4       12
Soybean       45-55        13        13         11

Table 16-2
Nutritive values (crude protein, neutral detergent fiber, and
digestible energy concentration) of some feeds. All data are
on a dry matter basis. Neutral detergent fiber (NDF) represents
the cell wall of the forage. More NDF results in less intake by
livestock. Board on Agriculture (2001).

                                      Digestible              Neutral
                                        energy      Crude    detergent
Feed                                  (Mcal/kg)   protein %   fiber %

Forages
  Barley silage                          2.68       12.0       56.3
  Corn silage                            2.97        9.2       47.3
  Grass hay (<20% legumes)               2.57       13.1       61.9
  mid-maturity
  Grass silage (<20% legumes)            2.61       15.8       61.2
  mid-maturity
  Grass-legume mixture, hay (40-60%      2.57       14.4       54.0
  legumes) mid-maturity
  Grass-legume mixture, silage           2.51       17.2       53.7
  (40-60% legumes) mid-maturity
  Legume hay (>80% legumes)              2.62       17.9       45.3
  mid-maturity
  Legume hay (>80% legumes)              2.77       19.7       40.0
  vegetative
  Legume silage (>80% legumes)           2.58       20.0       45.2
  mid-maturity
  Legume silage (>80% legumes)           2.73       21.1       39.5
  vegetative
  Sorghum silage                         2.63       16.5       56.6

Concentrates
  Barley grain, rolled                   3.64       12.4       20.8
  Beet pulp, dried                       3.03       10.0       45.8
  Brewers grain                          3.38       29.2       47.4
  Corn grain, ground dry                 3.85        9.4        9.5
  Cotton seeds                           3.55       23.5       50.3
  Sorghum grain, dry rolled              2.83       11.6       10.9
  Soybean meal                           4.16       53.8        9.8
  Soybean seeds, whole roasted           4.72       43.0       22.1
  Sunflower meal                         2.90       28.4       40.3
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Publication:Introduction to Agronomy, Food, Crops, and Environment
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Date:Jan 1, 2009
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