Method for Calculating Corn Yield (Mg/ha) from Experimental Field Data at Plot Level
There is a corn experimental field as shown below. While regular corn farmers typically sow the entire field at once without dividing it into plots, researchers divide the field into plots and differentiate treatments to derive experimental results.
The yield data obtained from field experiments should be in the common unit used by farmers, which is Mg/ha or bu/acre. However, our experimental field is not as large as a hectare (ha). Even if a certain experimental field is as large as a hectare, it may contain multiple experimental treatments within that hectare area, making it impossible to determine the yield (Mg/ha) for each individual treatment.
Up-scale the corn yield
Today, I will explain how we can predict (up-scale) the corn yield (Mg/ha) using the data obtained from the corn experimental field at the plot level. Now, let’s continue the discussion by focusing on a single plot among the numerous plots.
The area of a plot with a width of 3m and a length of 9m is indeed 27 square meters (m²). I understand that there might be slight variations in planting density across different regions, but as a general guideline, in North America, the planting density for corn is typically around 30,000 to 35,000 plants per acre. The general unit of measurement for area in many countries is ha, so the size of an acre may not be immediately understandable. 1 acre is 0.40 ha.
1 acre = 0.40 ha
This unit is too large to apply to individual plots, so from now on, let’s discuss the measurements in square meters (m²). According to Ontario, Canada, as a general guideline, there is an approximate planting density of about 34,000 corn plants per acre.
1 acre = 0.40 ha = 4,000 m2
If we calculate based on 1 acre = 0.40 ha = 4,000 m², it is generally expected to have around 34,000 corn plants cultivated on an area of 4,000 m². This means that there would be approximately 8.5 corn plants cultivated per m². Given that the area of the plot is 27 m², we can estimate that there would be around 230 corn plants cultivated in the plot. Since the plot has 4 rows, each row would have approximately 58 corn plants cultivated.
Typically, when determining the target planting density (34,000 corns/acre) and sowing corn in experimental fields, the following method is used: The tractor speed is adjusted to ensure that 58 seeds are sown within a distance of 9m.
When discussing planting density in corn physiology research, here are some notable numbers to remember.
3,4000 - 35,000 plants/acre 85,000 - 90,000 plants/ha 8.5 - 9.0 plants/m2 It is convenient to remember that a rough estimate for the target planting density is around 90,000 plants per ha, and approximately 9 corn plants are cultivated per m².
Now that we are ready to harvest the corn from the experimental field with a planting density of 34,000 plants per acre, we need to measure the yield. While it would be ideal to harvest and measure the yield of all the corn plants, we may not have the time or resources to do so. Therefore, we will need to estimate the yield through sampling and then scale it up to a specific unit.
Different research groups may have different methods for this process. The method I am introducing is just one among many possible approaches.
1) Measure a distance of 5m and harvest all the corn plants from the inner two rows among the four rows
When we say ‘harvesting the corn’ here, it means harvesting the corn cobs. We will harvest all the corn cobs in each plant. Then, we measure the weight of the entire cob, which will be the total cob fresh weight.
2) Randomly select 10 cobs from the harvested corn cobs
The next step is to randomly select 10 cobs from the harvested corn cobs. Then, measure the weight of these 10 cobs. This weight will be the fresh weight of the 10 cobs.
3) Measure the dry weight of the 10 corn cobs
Store the corn cobs in a drying oven at approximately 70°C for about 2-3 days to remove all moisture. Afterwards, measure the weight of the cobs, and this measurement will give you the dry weight of the 10 cobs.
4) Moisture calculation
Calculate the moisture content of the harvested corn. Since we have the fresh weight of the 10 cobs and the dry weight of the same 10 cobs, we can easily perform the following calculation:
moisture (%) 1 - (dry weight / fresh weight)
This formula will give us the moisture content of the corn as a percentage.
5) Measure the kernel dry weight after shelling
Shell the 10 corn cobs to obtain the weight of the kernel dry weight. Then, calculate the ratio between the kernel dry weight and the dry weight of the 10 cobs.
6) Calculate the total grain weight of the 5m sampling interval
The next task is now to calculate the total grain weight of the 5m sampling interval. We calculate it using the following formula.
{Fresh weight * (1 - moisture %)} * ratio of grain
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0.845
i) Remove moisture from the fresh weight => Fresh weight * (1 - moisture %)
ii) Then, multiply that value by the grain ratio. The yield of corn is determined by the grain weight, so the weight of the bare cob should be excluded.
iii) Divide the calculated value by 0.845.
The value of 0.845 is used as a divisor because it is a correction factor based on the moisture content of corn. Corn typically contains 15.5% moisture. For example, if you have 100 kg of corn, this weight may have undergone some loss due to drying. If the dry weight of corn is 100 kg, it corresponds to 118.3 kg at 15.5% moisture content. To adjust the value, we divide it by (1 – 0.155), which is approximately 0.845. Hence, we divide by 0.845.
7) Upscaling to yield (Mg/ha)
The calculated value from step 6 represents the weight of corn in the 5m interval sampling. Now, we will upscale this value to Yield (Mg/ha).
To determine the weight per hectare, we first need to calculate the area of the sampled interval. The height is 5m, and the width is 1.5m. Since the spacing between rows is 0.75m, half of that would be 0.375m, resulting in a width of 1.5m (= 0.75 + 0.375 + 0.375).
The corn grain weight we calculated at 15.5% moisture corresponds to an area of 7.5 m2 (= 5m * 1.5m). Now, let’s find out how much this weight would be per hectare.
To convert from m2 to ha, we divide the area by 10,000 (since 1ha = 10,000 m2). Therefore, the weight per ha would be the weight divided by 7.5m2 divided by 10,000.
Yield (kg/ha) = corn grain at 15.5% * (10,000 / 7.5 m2)
Practice
If you well followed so far, from now, let’s calculate the yield using actual data.
■ The fresh weight (kg) of the three corn varieties harvested from the 5m interval are as follows:
| Variety | Fresh weight | 10 cobs fresh weight | 10 cobs dry weight | moisture (%) | Kernel dry weight | Ratio: grain to cob weight |
| CV1 | 10.6 | |||||
| CV2 | 11.2 | |||||
| CV3 | 13.0 |
■ and I randomly selected 10 corn cobs to measure their fresh weight (kg).
| Variety | Fresh weight | 10 cobs fresh weight | 10 cobs dry weight | moisture (%) | Kernel dry weight | Ratio: grain to cob weight |
| CV1 | 10.6 | 1.8 | | | | |
| CV2 | 11.2 | 2.0 | | | | |
| CV3 | 13.0 | 2.1 | | | | |
■ Now, after storing these 10 cobs in a dry oven for 2-3 days, I measured their dry weight (kg) and calculate the moisture content (%) of the corn grains.
| Variety | Fresh weight | 10 cobs fresh weight | 10 cobs dry weight | moisture (%) | Kernel dry weight | Ratio: grain to cob weight |
| CV1 | 10.64 | 1.80 | 1.41 | 21.6% | ||
| CV2 | 11.21 | 2.05 | 1.59 | 22.2% | ||
| CV3 | 12.97 | 2.07 | 1.63 | 21.4% |
For example, for CV1,
1 – (1.41 / 1.80) = 21.6 %
■ After shelling the corn cobs, measured the weight of the corn grains.
| Variety | Fresh weight | 10 cobs fresh weight | 10 cobs dry weight | moisture (%) | Kernel dry weight | Ratio: grain to cob weight |
| CV1 | 10.64 | 1.80 | 1.41 | 21.6% | 1.23 | |
| CV2 | 11.21 | 2.05 | 1.59 | 22.2% | 1.41 | |
| CV3 | 12.97 | 2.07 | 1.63 | 21.4% | 1.43 | |
■ and then calculate the ratio between the grain weight and the cob weight.
| Variety | Fresh weight | 10 cobs fresh weight | 10 cobs dry weight | moisture | Kernel dry weight | Ratio: grain to cob weight |
| CV1 | 10.64 | 1.80 | 1.41 | 21.6% | 1.23 | 87.2% |
| CV2 | 11.21 | 2.05 | 1.59 | 22.4% | 1.41 | 88.7% |
| CV3 | 12.97 | 2.07 | 1.63 | 21.3% | 1.43 | 87.7% |
For example, for CV1,
1.23 / 1.41 = 87.2%
■ Then calculate the weight of the grains in the 5m interval considering the 15.5% moisture content.
| Variety | Fresh weight | moisture | Ratio: grain to cob weight | Grain @ 15.5% moisture |
| CV1 | 10.64 | 21.6% | 87.2% | 8.60 |
| CV2 | 11.21 | 22.4% | 88.7% | 9.12 |
| CV3 | 12.97 | 21.3% | 87.7% | 10.60 |
For example, for CV1,
{Fresh weight * (1 - moisture %)} * ratio of grain
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0.845
((10.64 * (1 – 21.6%)) * 87.2%)) / 0.845 = 8.60 kg
■ upscale the weight of the 5m interval with 15.5% moisture content to the unit of Mg/ha.
| Variety | Grain @ 15.5% moisture | 5m sampling area (m2) | Yield (kg/ha) | Yield (Mg/ha) | Yield (bu/acre) |
| CV1 | 8.60 | 7.5 m2 (= 5m * 1.5m) | 11,466.7 | 11.5 | 182.3 |
| CV2 | 9.12 | 7.5 m2 | 12,160.0 | 12.2 | 193.3 |
| CV3 | 10.60 | 7.5 m2 | 14,133.3 | 14.1 | 224.7 |
For example, for CV1,
8.60 * (10,000 / 7.5) = 11,466.7 kg/ha
Let’s also convert the yield to the unit of bushels per acre (bu/acre), which is commonly used in North America. We calculate that 1 kg/ha is equal to 0.0159 bushels/acre.
By going through these steps, we will be able to discuss the yield of the corn we cultivated in the plot in terms of Mg/ha or bu/acre.
Reference
□ Corn Plant Density Effects on Silage Quality
□ Converting Wet Corn Weight to Dry Corn Weight
