Module 1. Introduction to the Wheat Crop
Lesson 2.1: Before planting
To grow a healthy wheat crop, it is important to make an Integrated Pest Management plan in advance and consider all the phytosanitary control practices that should be applied, from before planting to after harvest. IPM should include all the agronomic practices helpful in minimizing the impact of weeds, diseases and insect pest attacks, for the purpose of obtaining better yields and higher profits.
Before planting, the first decision to be made by the grower is to define the type of wheat to be planted: spring or winter. There are several aspects to consider that have an impact on this decision: the geographical conditions of the farm, experiences with prior crops and their respective yields, the production costs and the market prices for each type of grains. He cannot also ignore factors such as soil fertility, available hand labor, soil preparation and harvest and post-harvest, among others. He should always keep in mind that crops are dynamic and agronomic management practices could change according to each region and the forecasted climate during that growing season.
In Australia, the Grains Research & Development Corporation in Victoria published the different types of winter wheat Victorian Winter Crop Summary 2015
2.1.1 Field selection and climatic factors
In general, wheat grows best on flat topographies and well-drained soils, therefore, the field selection is an important step for a successful crop. When the initial agronomic management plan is being prepared, considerations such as: accessibility of machinery, irrigation availability, drainage, fertility, erosion, rotation, residues from prior crops and extension of the field, should be taking into account. It is important to locate as close as possible the facilities according to the needs for processing and marketing the wheat.
The type of wheat is sectioned considering the agro-ecological conditions, such as: latitude, altitude, rainfall and temperature. Depending on the available varieties, in some cases wheat grows best under climatic conditions dominated by rainy winters or dry summers and in other cases some materials grow during the periods of greater precipitation in the fall and early spring.
In Kansas (USA), low temperatures affect the wheat crops and cause “winterkill”. The early freezes during spring affect the growing points of the plants and the late freezes cause sterility. High temperatures damage the plant during the grain filling period and the kernels shrivel and ripen prematurely. Also, high temperatures during the fall cause poor tillering development and during winter, they stimulate wheat growth. The plants may be affected by consecutive low temperatures.
When a dry period occurs at the beginning of the wheat growing season it is possible to observe moisture stress. In soils with good moisture retention capacity stress is not observed because a few showers keep the soil moist. During very dry periods with precipitation under the norm, it is necessary to resort to irrigation to avoid yield loses, because during very dry periods sterility may occur.
Strong winds break wheat stems causing lodging. Wind with soil or sand particles causes abrasion damage and may even cause leaf burn. Wind damage can be sometimes confused with that caused by static electricity, because it produces burning on the margins or the tips of wheat leaves.
Hail damage is going to depend on the extent and severity of the hail impact, the growth stage that the crop is in, and on the phonological characteristics of the planted variety. Wheat is most susceptible to hail between the germination stage and the milk stage. Injury during the early grain development stages stops its development and destroys it; high hail severity can remove leaves and break the stems.
High seed and environmental humidity during harvest time can cause the germination of some grains. This phenomenon called “pre-harvest sprouting” damages the quality of the grain, mainly those used for making bread.
Case study on climate change impacts on wheat production
2.1.2 Soil Analysis
The first step before establishing the crop is to determine the fertilization needs through soil analysis, which defines the physical and chemical characteristics of the fields. To perform the soil analysis, a number of representative samples of the area to be planted should be taken.
There are two basic objectives with the soil samplings: first, establish the physical and chemical properties including the pH, and second define the nutrient content and their balance in the different fields. From the results of the analysis and the accuracy of the fertilizer rate recommendations depend the crop yields and the conservation of the soils.
Depending on each country, there are public and private soil testing labs that offer specific services, from soil sampling and up to the analysis. The analysis may be a basic fertility test (pH, organic matter, inorganic nitrogen, extractable phosphorus and exchangeable potassium), to specific procedures such as foliar analysis for micronutrients and nitrate-nitrite levels.
For example, the North Dakota Service University recently published the winter wheat fertilization recommendations for North Dakota, USA Fertilizing Winter Wheat
According to the private or public extension service recommendations, growers should decide on the fertilizer brand and application method.
When uniform fertilizer application is selected, samples should be collected from subareas within fields because they are not completely uniform. These subareas are determined based on land slope, degree of erosion, soil type, past cropping systems and any other factors that can influence the level of nutrients in the soil.
When variable rate fertilizer application is selected, use any of the soil grid sampling methods or sampling based on specific zones or sites (“zone-based sampling”). Grid sampling is expensive and time-consuming, but can provide useful information for the correct site-specific fertilizer application for several years. Zone-specific sampling is based on spatial information through yield maps, soil surveys, and aerial photographs.
It is important to use the same sampling depth of 0 to 20 cm because fertilization recommendations for all nutrients, except nitrogen, are based on nutrient levels found on the surface soil sample.
In Nebraska, it is recommended to use surface and subsurface samples (deeper than 20 cm) to accurately estimate the nitrate-nitrogen ratio in the root zone, because nitrogen in the nitrate form moves easily with water in the soil and will leach into the subsoil.
In all cases the laboratory instructions should be followed to do a representative soil sample collection of the field using a soil probe. Take 15 to 20 surface samples at random from a field of less than 15 hectares. Mix and homogenize well the subsamples in a plastic bucket and separate a maximum of one (1) kg to send to the lab for analysis. Identify each sample and send them to the lab within the next 24 hours. For wet samples, first let them dry for 24 hours at room temperature and then send them to the lab for analysis.
2.1.3 Soil preparation / tillage
Land preparation to get the best seedbed for wheat depends on several factors: time availability, hand labor, physical condition of the soil, residues from the preceding crop, machinery, water availability, slope of the field, climatic conditions, irrigation system and the growers’ attitude towards tillage.
The establishment of wheat plants requires a well pulverized but compact seedbed to get uniform germination and moisture retention. During soil preparation care must be taken to avoid soil erosion, which depends to a great extent, on the management of the preceding crop residues or harvests. Besides, the incorporation of weeds, stubbles and cover crops should be worked to increase organic matter content.
In general, there are three types of soil preparation systems: 1) traditional or conventional tillage, 2) minimum tillage and 3) no-tillage. Nowadays, no-tillage is a very common practice, but before using any soil preparation system, soil compaction and preceding crop residues should be addressed.
Compaction causes the soil to water saturate easily, reduces air movement through pores and plants may suffer water stress, and consequently yields are reduced. When soil compaction exits in a dry field, the use of a subsoiler can break up the deep compaction, while the plow and the cultivator can break up shallow compaction. When the soil is humid, these operations could worsen compaction.
Residue management is difficult and in some cases, the method selection depends on the preceding crop; in most cases growers use one or two passes with a disk or chisel. This is followed by another disking or field cultivation close to planting time. When the preceding crop is a row crop, the residue may be left until late summer and then a field cultivator is used before planting, because the longer the residues remain on the soil surface, the more they protect the soil from erosion and conserve moisture. It is very important for IPM to conduct a phytosanitary inspection of the residues, plant diseases resistant varieties or to use fungicide treatments.
In conventional tillage, one pass of moldboard plow or deep tillage is done to help decompose the residues and to keep the soil surface free of debris. The soil should be plowed as deeply as possible, to help break up compaction and reduce the risk of herbicide carryover. Disk plowing and a pass with a chisel complete the seedbed preparation. Soils should not be tilled when moist because this increases soil compaction, the formation of large clods and the physical conditions change unfavorably for wheat growth.
Minimum-tillage and direct seeding are characterized for being low soil impact systems, and they lower soil preparation costs as compared to conventional systems. The crop residues that remain on the soil surface prevent soil erosion and conserve moisture. Soil preparation usually consists of applying herbicide, and the seed is planted directly through the residue of the preceding crop. For soil preparation in the traditional methods, residues of previous crops are buried with the plow’s discs, while in minimum tillage these residues remain on the surface and the planting equipment must have a drill capable to cut through those residues. When the residues re sprout or emerge they must be eliminated with post-emergent herbicides and it is recommended to apply the minimum dose of fertilizer or lime.
2.1.4 Cultivar selection
Selecting the appropriate variety for the region where the field is located is a very important decision; the climatic changes and the variability of the weather conditions are difficult to predict. Nowadays, there are many factors to take into account such as: high yield, straw strength, pest and disease resistance, grain quality, crop rotation, early maturity required for double cropping system, expected field problems and winter hardiness.
When the land area to be sown is very extensive, it is recommended to not plant just one variety, but rather select different varieties, to avoid homogeneity and that the phytosanitary problems are generalized, increasing the management costs. Before making the decision on the selected varieties, it is important to find out about experiences with prior crops and the behavior of the genetic heritage of the varieties. Much of the information may be obtained from the private and public seed producers, experiment station field researchers, performance test, private and public publications, or the experiences of neighbors.
Wheat Cultivars for California (University of California, 2011)
2.1.5 Resistant plants
Selecting plants with genetic resistance to insects and diseases is an important element to implement Integrated Pest Management. One must be aware of the pest and disease problems in the region to select the appropriate variety. Frequently, soilborne or leaf diseases such as rusts, sucking, piercing and leaf boring insects, or virus vectors can be present in any wheat crop. If possible, a variety must be selected that is resistant or tolerant to one or more of these phytosanitary problems, which will reduce the production costs and increase the yields.
2.1.6 Other characteristics
There are several characteristics that the grower should seek in a wheat variety, depending on the environmental resources, the regional phytosanitary problems and the farm location. From a good selection here depends the profitability of the enterprise.
Varieties that do not lodge easily are excellent in regions with strong winds, especially when the variety is ripening. Besides, wheat can be damaged from cold temperatures that happen in the fall before wheat hardens or early in the spring. Varieties with winter hardiness or with resistance to freeze damage should be selected.
It is recommended to select early maturing varieties when planting a rotation crop to escape from the hot winds or drought in the spring. Depending on the extension of cultivated land, the harvest should be spread in several times and in this case, growers should select varieties with different maturity times. If the wheat is planted for bread manufacture, the quality of the grain must fit the needs of millers and bakers to have good product demand. Grain quality is a desirable trait in wheat.
Finally, some specific grower needs must be considered such as, soil acidity resistance, grazing potential, semi-dwarf varieties, awn-less varieties, materials with high test weigh or with high straw yield.
2.1.7 Seed sourcing
Once varieties have been selected with all the desired characteristics, it is best to get “certified” or “registered” seed at a commercially recognized distributor in the region. Using guaranteed quality seed is the foundation for achieving excellent germination and subsequent stand establishment, or the manifestation of its attributes in the crop. Then we can say that the profitability and sustainability of the crop depends on the choice of a quality seed, true to the attributes of each variety, free of seeds of other varieties or weeds, foreign matter, disease-tolerant or resistant, and with good yields. Certified seeds ensure the origin and quality; because they must be authorized and labeled by official institutions, in accordance with the law. The packaging must contain information about the characteristics of the variety, the germination percentage, phytosanitary behavior, purity percentage and inert material.
The thousand kernel weight (TKW) is a good method or a good parameter to evaluate seed quality and to estimate the quantity of seed needed for the desired planting density. The weight of each seed depends on the variety and can range from 30 to 50 mg, which equates to 34.000 to 20.000 seeds per kilogram. Then, we could affirm that a TKD 40 mg/seed ensures 25000 seeds/Kg, considered an optimum parameter defining good seed quality.
Lesson 2.2: Sowing
Any sowing method should be based on the availability of equipment, time, labor, costs and the proper planting dates. Besides the calibration of planting equipment, the correct number of seeds to be planted per hectare must be taken into account, following the recommendations of the seed producer, which are based on field research that was conducted earlier.
In general, wheat is planted using a grain drill to obtain good germination and maximum yields. The drill assures good seed-to-soil contact, promotes rapid germination and emergence, results are more uniform and optimal, reduces winter injury, and increases yields over broadcast seeding. The drill can be used for conventional tillage, minimum tillage and no-tillage, depending on field conditions. Conventional tillage provides a fluffy, smooth seedbed and a more uniform depth.
Broadcasting or hand seeding over prepared soil is another fast wheat seeding method. Seed is distributed on the soil surface with a fertilizer spreader and incorporated into the soil with tillage using disks or cultivators. Broadcasting is a good option in emergency situations due to bad weather or when sowing should be delayed to the end of the planting date. This method produces an uneven seed placement in the soil, which results in uneven emergence or poor stand establishment, which reduces yield. Seeds can go to a 10 cm depth in the soil and even though the seed germinates sometimes, it cannot emerge to the soil surface. Some seeds are planted very shallow or on the soil surface and often do not survive in very dry or very wet soils. One method of improving stand uniformity is to broadcast seed in two passes across the field, planting half of the seed in the first pass and the other half in a second pass, perpendicular to the first.
Video on ploughing and sowing of Wheat Seed (Cumbria, UK)
2.2.1 Planting dates
Climatic conditions and agro-ecological zones vary greatly across the North and South hemispheres and within wheat growing countries all over the world, therefore it is recommended to plant at different dates, depending on the location. Planting dates affect final yield of a particular wheat variety and influence the phonological development of the crop, the available soil moisture for the plants, the temperature, photoperiod, use efficiency and availability of fertilizers, duration of the photosynthetic process, and the probability of incidence and severity of some diseases.
In general for winter wheat varieties, September and October are the proper planting dates for the northern hemisphere, while May and June are for the southern hemisphere. Growers try to plant wheat at a given time so that the seedlings and their roots develop well and that tillers are formed before winter dormancy, which enables plants to develop better. Planting too early can result in excessive growth that could lead to lodging, greater disease severity and increased insect attacks. When planting too late, much of the fall growing period for wheat development is missed, the plants suffer much winter damage, the yield is reduced and the kernels mature later.
Planting practices in Wheat Management in Kentucky (University of Kentucky)
Spring Wheat Planting Guide (SDSU, 2012; chapter 5)
2.2.2 Plant density
Seeding rates to obtain maximum wheat yield will depend on multiple climatic conditions, such as precipitation and temperature. Also, it will depend on the seed size, weight and germination; on the soil texture, water retention, nutrients and fertility; and on the planting date, method and calibration of the equipment.
Wheat seeding rates vary from 150 to 500 seeds per square meter for the different varieties, and depending on the climatic conditions. This should result in 130 to 400 wheat plants per square meter, depending on the germination and emergence rates and on the soil moisture. Mellado (2007) points out that when planting 400 to 500 seeds per square meter, it is possible to obtain from 500 to 600 heads per square meter, which is a good density to obtain good yields. The University of Kentucky (2009) recommends planting 320 to 380 wheat seeds per square meter which will result in the desired plant population of 270 plants per square meter.
In general, seeding rate expressed in Kg/ha is equal to the number of desired plants per square meter, multiplied by the mean weight of the seed to be planted in mg, and divided by the seed germination rate.
Seeds should be planted into the soil at a depth of 5 cm as a maximum, considering the soil moisture; if the soil is too dry planting may be done slightly deeper than when there is moisture. Seeds that are planted very deep present delays, resulting in plants with less vigor, lower initial vegetative growth, and reduced tillering. Seeds with short coleoptile development will die when planted too deep, on the other hand, when planting is shallow, it results in uneven seed germination and emergence, and greater susceptibility to winter injury. It is very important to ensure there is good seed to soil contact when no-tillage is used, because the crop residues do not allow for good contact.
In most of the cases, wheat is planted in rows 15 to 18 cm apart. However, research in general has shown greater yields with wheat at higher density in 10-cm rows to get better leaf area distribution, increase photosynthesis and produce a greater number of heads per square meter.
Lesson 2.3: Soil management
Soil management comprises a series of agronomic practices such as crop rotations, residue management of the previous crop, tillage, fertilization, liming, irrigation, and avoiding erosion and compaction, to create good physical and chemical conditions for crop growth and development, and to obtain the maximum yield at harvest.
Water is essential for growth and development of wheat; the young plants contain 95 % moisture and the grain 12 to 15% at harvest maturity. Water transports nutrients through the xylem driven by the transpiration process of the leaves. When the plant is well hydrated all the biochemical and physiological processes run easily maximizing photosynthesis, respiration, nutrient assimilation and protein formation.
It is estimated that the wheat crop makes a deficient use of water since it utilizes 500 liters of water to produce 1 Kg of dry matter. This means that about 1200 liters of water are required to produce 1 Kg of grain with 12% moisture. For this reason, in dry lands the wheat grower should be aware to make a rational use of the water to obtain better yields.
During its development, wheat roots can grow and penetrate in most cases 25 cm of the soil profile and some reach up to 1 meter, presenting rapid growth during the spring after breaking of dormancy. When soil water depletion levels approach 80%, wheat yield starts being impacted at most development stages. Then, it is recommended to maintain soil water at about 50% moisture to sustain optimal development during the whole growth cycle.
Water is very important for good development of wheat plants from emergence to physiological maturity. Water favors the development of all plant structures, and increases stem growth and elongation, which break easily when too developed. Peak daily water use rates during the whole grain development cycle for wheat are 1.3 cm per day, but on average the normal use rates will be around 0.9 cm per day.
A lack of water during the vegetative phase will hinder its good development and reduce tillering and plant height, because of reduced cell growth; and during flowering it will decrease yield, because of less number of grains per head; and during the grain filling period it will produce small or empty grains.
Total water needs for wheat can vary greatly depending on weather conditions, but are in a range of 40 to 65 cm per plant for a wheat crop without water limitations. About 40% of water use will occur in the vegetative stage from emergence to the beginning of rapid growth in the spring, another 20% from the beginning of the reproductive stage to flowering, and 40% among flower, grain in the milk stages.
Wheat can be grown as an irrigated crop or as an upland crop. However, when irrigation is available during the rainy season, it should be measured also taking into account, the stored water availability in the soil profile. In upland crops, variety selection, planting date and soil characteristics are important for a successful harvest.
Surface irrigation is the most used type of irrigation, but in some cases, sprinkler systems have advantages over surface systems. The soil water holding capacity has a large influence on deciding which strategy will be successful. Soils with low water holding capacities will require several irrigation applications during the crop cycle; therefore, sprinklers systems will be more suitable for this situation than surface irrigation. The important thing for irrigated crops is to maintain soil water above 50% depletion.
Crop Water Information on Wheat (FAO, 2015)
Soil fertility is a combination of its chemical and physical properties, expressed in the mineral content in the soil, its biological fertility of organic matter and the structure, porosity and density of the soil.
Fertilizer applications allow the provision of the adequate nutrients at each stage of wheat development and are essential to reach the maximum economic yields. So, the first step in setting up a fertilizer management program is soil testing. Except for nitrogen (N), the fertilizers and liming need decisions will be based on soil test results. In addition, climatic conditions, crop needs and cultural systems should be taken into account when developing a fertilization program.
In general, macro elements such as nitrogen (N), phosphorus (P) and potassium (K) are the primary nutrient needs. However, in some cases other macronutrients (Ca, Mg and S) and micronutrients (Zn, Mn, Cu and B) need to be applied. In soils with very low pH, liming is needed and wheat has been found to respond very well.
Nitrogen is one of the most important elements for optimum wheat production. Nitrogen deficiency produces chlorotic plants with a few tillers, while N in excess causes lodging, increased disease incidence and severity, and therefore lower yield. Besides, excessive N contaminates ground and surface waters with negative environmental consequences.
Nitrogen recommendation rates must be calculated for each field, they are based on the phonological development of the crop, soil texture, climatic conditions and expected yields. In general, a pre-plant application and a late spring one are the recommended times for nitrogen application in winter wheat. It is recommended to incorporate Nitrogen during tillage or inject it directly into the soil. Spring applications depend on the moisture conditions and are important during vegetative development. The application during the reproductive stage may increase protein content of the grain, but have less effect on yield.
Phosphorus is essential for root growth, vegetative development, tillering, early heading, grain fill, timely maturity, and winterkill resistance. Soil tests are essential to determine the proper rate of phosphorous that needs to be applied. Phosphorus should be applied and incorporated in the soil, injected in concentrated bands before planting, or banded at planting. Band applications with the seed at planting or injected pre-plant are more effective.
Another alternative would be to band apply both nitrogen and phosphorus fertilizers before planting. Dual application of N and P with tillage saves time and allows placing the P in the root zone for good utilization.
Potassium helps to reduce the incidence of some diseases and increases straw strength, which helps reduce lodging. A soil test is necessary in order to determine the proper rate of K fertilizer. Potassium may be applied before or at planting time, but some growers prefer to apply it after plant emission. Potassium application with the seed should be avoided because of germination damage. The selection of K fertilizer source should be based on price, availability, and adaptability to the farm operation.
All nutrient applications must be based on a soil test, fertility records from the field and prior experience about nutrient deficiency and wheat response. It is important to say that some nutrient deficiencies are best determined by analysis of plant tissue sampled early in the spring.
Other resources on nutrient need for cereals including wheat are:
Nutrient Management for Agronomic Crops in Nebraska
2.3.3 Organic matter
Decomposed organic materials are used as a complement of the inorganic fertilizers. They are organic residues, which include materials such as sludges, manures, plant materials, compost and industrial byproducts. The wheat grower can incorporate these organic materials into a soil management program. The grower must consider how to estimate nutrient values of organic materials and how to effectively apply the materials.
Unlike fertilizers, organic materials are not uniform and in many situations they are not completely homogeneous. Manure consists of many nutrients and it will not contain the exact ratio of nutrients needed for every field and the wheat crop. The grower must decide which nutrients will be applied as manure and which nutrients will be supplemented with other sources. The best way to accurately estimate the nutrient content of manure is to take samples and analyze them before application.
Nitrogen is a rich nutrient in organic matter, but it is easily lost during storage, handling and application. How much is available depends on how it is applied and on the environmental conditions after application. When manure is applied, other nutrients are incorporated, but to estimate the quantity that should be applied and to determine the manure application rate needed to supply certain N recommendations is not so simple. The goal of an efficient manure management plan is to combine organic materials and inorganic fertilizers so that the combined materials provide all the nutrients needed by the crop without excess.
Incorporating manure enriches the soil because it improves its physical, chemical and biological conditions. It should be well decomposed before taking it to the field, to avoid odors and health problems. It is most common to apply solid manure, which should be done as uniformly as possible; some growers prefer to apply it as slurry.
Lesson 2.4: Harvest, storage and processing
Defining exactly the time of physiological maturity of wheat is the most important decision for high profit results during harvest. Many factors should be taken into account; harvest day should be dry, the temperature high, and the relative humidity low. The farm should have installations with good drying and storage capacity.
In most regions where wheat is grown in the world, harvesting time coincides with a period of high temperature and dry climate, which allows harvesting the grain with 11 to 14% moisture and no artificial drying is necessary. However, when the dry conditions do not coincide with the harvest, the moisture content range may be 12 to 15 percent. On the other hand, when harvested early and the grain has higher moisture it is possible to dry it artificially, but it should be done quickly to prevent spoilage and the arrival of pests and diseases during storage and transportation.
Wheat harvest should begin as soon as the crop has field dried enough that it can be handled safely. A well calibrated hand held moisture meter is very useful to give a quick determination of the crop condition.
All conventional or modern high capacity combines must be calibrated and adjusted. All these equipment have an operator´s manual to do the adjustments in the field, particularly the engine speed, to avoid losses or damage to grain quality. It is important to combine the basic functions during harvest, such as: cutting of the heads, feeding the hopper, threshing the grain, separating the chaff, cleaning the grain and measuring the yield. If for any reason any of these basic functions is not performed adequately, the others that follow will have problems and affect the yield. The wheat grower must check and make the necessary combine adjustments in cylinder speed, concave clearance, screen openings, and fan speed.
When calibrating the equipment it is important to measure field losses by counting loose kernels on the ground. One must look in front of the combine to measure pre-harvest losses (or the wheat kernels found under the combine), as well as count loses behind the combine to measure the threshing, and separation loses. Counting the number of kernels found per square meter, loses per hectare can be estimated, considering that a kernel may weigh 30 mg.
Poor combine adjustment can affect wheat grain quality mainly by physical damage and loses during the cleaning process. Physical damage may be: cracked, broken or squashed kernels that leave powdery residues that harbor insects and increase mold growth. Some of the damaged grain is eliminated during cleaning, but most end up in the back of the machine in the form of flour and small fragments. It is common to have 2 to 5% grain damage; if the percentage is higher, the cylinder/rotor speed in the threshing area of the combine should be checked, but they may also be caused in the transport system. If slowing the cylinder/rotor speed does not improve the grain sample, adjustment of the concave clearance may be needed.
Foreign material also contributes to a lower quality wheat sample. Some weed seeds are difficult to separate from wheat. A good way to help avoid this problem is to practice good weed control.
Freshly harvested wheat grain should be dried quickly to a moisture content of 14% or less within a 48 hours period to prevent sprouting or spoilage. Some drying equipment is used to quickly dry wheat with high moisture, greater than 17%. For commercial wheat, drying air temperatures should be below 65ºC; higher temperatures damage milling quality. Seed wheat should be dried at 55ºC or lower temperatures to avoid embryo damage which results in a very poor germination rate. Wheat for animal feeding may be dried at 80ºC or lower to avoid protein denaturalization.
Wheat stored on farm must be kept free of insects, fungi, rodents, and other pest to ensure acceptance by domestic and foreign grain buyers. Integrated pest management techniques during wheat storage require proper use of sanitation services, cleanliness, application of the proper fumigants when needed, good aeration, and frequent inspections to maintain the wheat quality. Sanitation is critical to maintaining wheat quality during storage. Totally remove grains of the old crop and physical, chemical or biological contaminants. Thoroughly sweep the bin to remove trash, clean, smooth and paint the walls and aeration ducts, to remove materials that may serve as refuge for insects or that may have molds. On the grain piles, only apply fumigants; preventive insecticides should not be applied directly on the grain or its packaging as it may contaminate it.
Good aeration allows cooling the wheat, which reduces insect reproduction ability in the grain and minimizes temperature gradients. The grain may be cooled using aeration with fans, but they need 80 to 120 hours to cool the grain depending on the airflow rate. The difference between the grain temperature and the outdoor air temperature should be a minimum of 5ºC before an aeration fan is turned on. Automated controllers for aeration fans automatically turn them on based on time and preset conditions.
The wheat harvest should be inspected at least every fifteen days, throughout the storage period to avoid deterioration by molds and insects. A system should be designed to permanently sample with the help of probes designed for that purpose, light traps, pheromones for insects, meshes for sifting the grain, moisture meters and thermometers.
Changes in moisture content, insect activity, strange odors, or temperature changes can best be detected by the frequency of inspections, which allow the adoption of timely control measures.
Mellado (2007) points out that temperature and grain moisture play an important role in wheat grain storage. If the storage temperature is less than 15°C and the grain humidity is lower than 14%, normally there is an excellent storage. If the temperature is less than 15°C and grain moisture is greater than 15%, some seeds may germinate prematurely. If the temperature is greater than 15°C and grain moisture is less than 14%, insect activity is high. Finally, if temperature is greater than 15°C and moisture greater than 15%, fungi develop quickly.
Lesson 2.5: Post-harvest
Wheat residues on the field must be managed carefully and rapidly, especially when a rotation will be made; there may be some seeds that germinate. These residues must be used as they are rich in nutrients, so they should be incorporated into the soil, so that microorganism can decompose them and liberate potassium, phosphorous and nitrogen. In general, crop residues play a very important role in soil conservation and improve the physical, biological and chemical conditions.
Residue management, through conservation tillage, is an effective tool for conservation and for reducing soil erosion. The soil surface covered with the residue is important to avoid erosion from runoff; crop residues shield the soil surface from the rainfall impact, thus reducing the amount of particle detachment.
Residues avoid the formation of crusting, as they keep the soils from compacting and allow more water to circulate in the soil, avoiding the formation of small puddles, reduce runoff velocities and the capacity to carry sediments. Standing residues increase snow catch during the winter and increase moisture storage for the subsequent crop. Wheat residues reduce wind erosion by reducing its velocity on the soil surface, creating small, calm air pockets that allow airborne particles to fall back to the surface. Standing residues avoid wind erosion.
In order to properly manage residues in the field after harvesting, most growers use one or two diskings or a chisel operation to incorporate the residues in the soil. This is followed by another disking or a field cultivator as planting time approaches. In other cases, to maximize moisture savings, the wheat residue is left undisturbed until the summer crop is planted with no-till into the stubble.
Wheat residue can be collected from the field and used in other crops or for different purposes. Wheat straw can be spread on the soil of plantation crops to control weeds and preserve soil moisture. It can be mixed with other substrates to compost it for the production of mushrooms or cattle feeding; some very crafty industries use them to make implements or bedding for cattle in barns; and finally, they may be used as an energy source or as biofuels.
Please see the Post-harvest compendium on wheat by FAO here Wheat Post-harvest operations