Yield-Harvest-Storage of Wheat

Yield, harvest, and Post-harvest handling of wheat

Yield potential of wheat

Grain Yield per hectare

The farmer’s goal is to have a final yield that deviates as little as possible from the yield potential of the wheat variety used. However, the final yield depends on the variety, the soil type, the water and nutrient availability, the weather conditions, the length of the cultivation period, the success of weed management and plant protection, and the moment and method of harvest. For example, winter wheat, as well as irrigated (or well rainfed) wheat, has higher yields compared to spring (2–2.5 tonnes per hectare difference) and dry-cultivated wheat (He et al., 2013). Generally, wheat grain yield can range from less than 1 ton per hectare to more than 10 tonnes per hectare. Most (winter) wheat-growing areas produce around 3 to 7 tonnes per hectare, with the World Guinness Record at 16.52 tonnes per hectare (2018, New Zealand). 

Straw Yield per hectare

Wheat is primarily cultivated for its grains. The straws of the plants usually remain on the field after harvest. However, some farmers choose to baling wheat straws and sell them as bedding for livestock to enrich their income. The straw yield depends on the wheat variety, the temperature, the water availability, the soil type, and combine header cutting height. Generally, the straw yield can range from 1.25 to 5 tonnes of dry matter per hectare based on variety, weather and combine harvest conditions(1).

Harvest time of wheat

The wheat harvest can start when the header can give a clean gain sample, and the crop has reached maximum kernel dry weight. This moment is when the crop has reached physiological maturity. From then onwards, the crop will accumulate no more yield, the stems are turning yellow, and the moisture content of the grains will start to decrease below 35-40%. Depending on the weather conditions, additional 10-14 days will be needed for the whole stem to dry out and the moisture content of the kernels to drop below 20% so that the mechanical harvest can start (2). However, most farmers prefer not to harvest at that moment and wait until the moisture content has dropped to the desirable 12,5%. Usually, the time they enter the field depends mainly on the moisture content of the grains and the availability of grain-drying facilities (3). When harvested manually, the grains can be collected when the moisture level is 25%, 4-5 days before they are dead ripe (4).

Except for the moisture content of the wheat kernels, the farmer can base his/her decision for the harvesting time on other factors like:

  1. The weather conditions
  2. The risk of disease dispersal. This is especially important for varieties susceptible to fusarium head blight. Farmers often scout the field and start harvesting even at 20% moisture content (1) in case of infection. During harvest, you can remove some of the grain that is more lightly infected by the fungus by turning up the air and blowing it out of the back of the header with the straw (5). Always keep the infected grains separately from the healthy ones.
  3. The risk of lodging and pre-harvest sprouting. Start harvesting first the fields with the highest risk and most susceptible varieties.
  4. The availability of personnel, machinery and appropriate dry and storage facility, etc.

Delayed wheat harvesting can lead to wheat sprouts, decreased flour quality and grain weight (dry matter), and losses due to shattering of the grains during mechanical harvest.

Wheat can be threshed by sickle, treading with cattle on the threshing floor, or power-driven thresher (combines). Most modern varieties mature-ripe evenly, making the mechanical harvest much easier and cost-effective. However, in some cases, farmers spray with glyphosate at the hard dough stage to accelerate the dry down of the crop (within a week from the application). However, this method has important disadvantages and is suggested to be avoided. Another technique used a lot in the past is swathing, but the high risk for pre-harvest sprouting has limited its use (6).  

Generally, it is best to start harvesting in the morning and not after a rainfall. Due to the high temperature, the low moisture content, and the operating machinery, there is a risk of fire. Be very careful and take preventive measures. 

Post-harvest handling of wheat grains

Safe, long-term storage of wheat grains is possible when the moisture content is below 12%, ideally 10%. When the seeds are stored in bags, the moisture content should be even less, close to 9% (7).

There are two main types of grain dryers:

  • Dryers using heat air in temperatures greater than 38oC (100 oF). This is a fast process and is more appropriate when the grains have been harvested with high moisture content.
  • Natural-air and low-temperature dryers. The grains are slowly dried in storage over 3-6 weeks. With this method, the dried grains have higher weight, germination, and less breakage (8).

Storage

There are different storage options like gas-tight sealable silo, non-sealed silo, grain storage bags, and grain storage sheds. You can examine the advantages and disadvantages of each choice before deciding where to store your grains. In case they decide to store the wheat seeds and to reduce the risk of losses due to infestation of the grains, the farmer or silo manager should follow specific steps and perform:

→ The silo (storing bins) should meet certain specifications. 

You can build, buy or rent an appropriate Storage Silo. The silo’s floor should be covered-paved, smoothed, clean, and dry with moisture insulation. Good aeration is also essential. You have to keep the area around the storage bins (3 meters or 10 feet radius) clean from grain residues and vegetation (9). The silo should be thoroughly cleaned and sanitized before placing the new grains. You can inspect the silo carefully for cracks or old grain residues (such as dust or false floors). Do not forget to clean the vents and repair any cracks or holes in the bins. Additionally, you can spray with certified (residual) insecticides on the floor and the walls of the silo before storing the new grains. You can ask your local certified professional agronomist. 

→ Place only healthy grains in the silo

The moisture content and the temperature the wheat seeds will be stored will definitely affect the length of the storing period. 

→ Chemical protection

From the harvest moment, the farmer can apply protective products with the following active compounds: Pirimiphos-methyl, (S) – Methoprene (10). You should always consult your local licensed agronomist. The grains can be treated with certified insecticidal dust if necessary. Usually, it is advised to perform such treatments before placing the seeds in the storing bins, and in this case, the storing will last more than a year. If the grains are stored in areas where the temperature and the humidity levels are high, then a grain protectant is important to be applied, sometimes followed by a capping treatment (application at the top of the grain mass).  

To protect from storage pests, it is common to fumigate and keep the room sealed for 24 hours. This technique is best to be applied only in gas-tight sealable storage to avoid the development of phosphate resistance in insects. For controlling rodents like rats, zinc phosphide is very effective. Some common grain disinfectants are Phosphine, Sulfuryl fluoride, and Dichlorvos. Products with such active compounds can control the pest population (all pest growth stages) in already infested grains. Some common grain protectants are Pirimiphos-methyl, Fenitrothion, Chlorpyrifos-methyl, Methoprene, and Deltamethrin (7).

Depending on the product the farmer will use, he/she should follow the product’s label instructions and of course ask the local licensed agronomist. 

→ Regular inspections

Extended on-farm storage of harvested seeds increases the risk of post-harvest losses due to pathogens (mold), rodents, and stored grain pests, even when the previous steps have been followed. When the temperature inside the silo is above 13-15.5 oC (55-60 oF), then the inspection should be performed more often (around once a week), while when the temperature is below 13 oC (55 oF), the inspection can be performed once every 2 weeks (9). Except for the visual inspection, the farmer should take representative samples from the grain piles and examine them for insect damage-presence and fungal contamination. Keep in mind that when the temperature is low, it is better to take sample from the center of the piles where it is more probable to find any insects at that time. In combination with sampling, the farmer can use probe traps to track the species and numbers of stored product insects.

Quality Tests

To facilitate the quality classification and specify the end use of the harvested grains, it is essential to perform quality tests (5). Such tests will focus on the following:

  • Protein content
  • Protein quality
  • Falling number
  • Impurities (Screenings)
  • Hardness
  • Moisture content
  • Weight: By determining the hectolitre weight of grains, the miller can predict the flour yield.

 As mentioned before, the grain quality is highly affected by the post-harvest handling and storage conditions as well as by on field management practices throughout the cultivation period of wheat. To reach the market standards, the farmer needs to take all necessary measures and be aware of the impact of each action on the grain quality characteristics. 

References

  1. https://www.canr.msu.edu/wheat/uploads/files/Wheat-101-report-2021-final%20-%20web.pdf
  2. https://extension.umn.edu/small-grains-harvest-and-storage/managing-wheat-harvest
  3. https://www.sepwa.org.au/phocadownload/projects/high_moisture/highmoisturebookfinal.pdf
  4. https://iiwbr.icar.gov.in/wp-content/uploads/2018/02/EB-52-Wheat-Cultivation-in-India-Pocket-Guide.pdf
  5. https://grdc.com.au/resources-and-publications/grownotes/crop-agronomy/northernwheatgrownotes/GrowNote-Wheat-North-12-Harvest.pdf
  6. https://extension.umn.edu/small-grains-harvest-and-storage/managing-wheat-harvest#how-to-identify-physiological-maturity-1406660
  7. https://grdc.com.au/resources-and-publications/grownotes/crop-agronomy/northernwheatgrownotes/GrowNote-Wheat-North-13-Storage.pdf
  8. https://extension.umn.edu/small-grains-harvest-and-storage/drying-wheat-and-barley#adding-heat-1407512
  9. https://site.extension.uga.edu/applingcrop/2019/08/protecting-stored-corn/
  10. https://ipm.missouri.edu/cropPest/2014/10/Insect-Management-Recommendations-for-On-Farm-Stored-Grain/

He, Z., Joshi, A. K., & Zhang, W. (2013). Climate vulnerabilities and wheat production.

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Principles for selecting the best Wheat Variety

Wheat Soil preparation, Soil requirements, and Seeding requirements

Wheat Irrigation Requirements and Methods

Wheat Fertilizer Requirements

Wheat Pests and Diseases

Yield-Harvest-Storage of Wheat

Weed Management in Wheat Farming

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