Homestead Skills--Calculation of Yield Metrics

After explaining the what and the why of the metrics, I elaborate on my methods for data collection and computation in the second section. This is a work in progress.

 

Yield Metrics

Comparison of crop performance depends on one's initial goal.  This is a discussion of different methods (metrics) of calculating yield, and for what goal it is best suited.

Yield for Land Usage

In larger farms, this would be bushels per acre or pounds per acre. At our scale, pounds per 100 square foot is often used as the weight will be in the range of typical household 'objects' that can be lifted and a square 10 foot on a side is easy to visual. Pounds per 1,000 square foot would be for a plot 31.6 ft on a side. 

Most commonly used for comparing yield, this metric does not take into consideration the necessary "inputs" such as equipment, calories, time, or fuel it took to grow that yield. Be cautious when comparing across a wide range of farming methods and seed technologies. Quoted yields for irrigated hybrids grown with a full range of chemicals will be different from those dry farmed with limited compost added.

Yield for Seed Quality

If the goal is to produce the largest seeds, previous work (a New England study) found that a wider spacing gave less net yield by weight, but larger seeds. The most often metric used in research is the weight in grams of a 1,000 seeds.  Not having enough time, we at Great Lakes Staple Seeds use the weight of 100 seeds, however, we make sure we scoop a random sample.

 

Yield for Labor Time

Cultivation methods relying on manual labor are constrained by how many hours of 'work' per unit of land is required. You might be able to 'work' 10 hours in the field, but can your body do this day after day?    And, how many other tasks are not getting done?    Even more problematic is that you need 'your time' to be available at the right time.    That is, having time to harvest the wheat two weeks after it was ready for cutting may not yield well if the grain has shattered and is now laying on the ground for the birds.

Pounds per hour worked would capture all of your 'working time' spent without a concern about the timing/schedule.

 

Yield for Energy Inputs

Simplest is to consider the human work (calories) it took to raise the grain in question.  Such a metric might be pounds per calorie worked.     This can be expressed as an efficiency, that is, 'human calories from grain" divided by "human calories it took to raise the grain".    This efficiency better be greater 100% or you will be consuming more food to raise the food you're eating, a recipe for starvation. 

Some may find the inverse more easily understood, 'calories worked' per pound of grain. 

Human and equipment requirements can be combined into the same base units.  Diesel can be made from oils that can be made from seeds grown on the farm, such as sunflower or soy beans.  Alcohol is also needed in this process.  Alcohol can also be made from seeds grown on the farm (currently not legal in the US).  Those seeds can be thought of as the human inputs that also went into raising the target grain.

 

Edge Effects

Plants growing on the edge of a block sometimes mature more slowly than the plot in general.  I see this at the 'end' of the row, and sometimes the entire row that boards a walking path. 

 

Measurement and Calculations

To quantify the yield, keep notes of the overall plot dimension in terms of length, width and how many rows.  Since our plots tend to be small, the edge effects may result in lower yield per square foot than a large field of the same variety.  

Sample data has been obtained by the following steps:

1. Using a tape measure, or number of poles of known l length, choose a length of the row at least a few feet away from the plot's edge, record this length.
2. Make a note of how many rows between 'this row' and the edge of the plot.  I define the 1st row as the row running along an aisle, or up against the next type of grains.   For example, a block of 10 rows of rye, then a block of 5 rows of wheat, then a block of 3 rows of emmer, then a block of barley, and so on.
3. Measure and record the distance from the row to row on either side of your test row.   For example, if the row spacing was about 9 inches, you should find approximately 18 inches, sometimes more, sometimes less.  I record this distance for both the start and end of the test strip.  In my data analysis, I will use the average and divide by 2 get the spacing between rows.  When planting in soil that is very dry, I will often increase my 9 inch spacing to 10 or 11 inches, providing a little less competition for water.
4. Count and record how many 'plants' are in the test length. The 'test length' runs needs to include half of the space between the first plant's neighbor, as well as from the last plant to its neighbor.  Heavily tillered plants can make this tricky.   If uncertain, pulling up some plants (roots and all) will you let you see how many base plants are in your strip.  From this count, we can now calculate the average space per plant.  Plant density is a strong factor that drives total yield from the plot.  Also, it impacts the leaf canopy's impact on slowing down weed growth.

 

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