Crop-Cutting Experiment: One Bund Plot, One Moisture Reading, One Expectation
You are assisting a crop-cutting experiment on wheat in a block of Nalanda district, Bihar. Four plots of 5 m × 5 m were marked in the selected field. After threshing and winnowing, the cleaned grain from the four plots weighed 4.2 kg, 3.9 kg, 4.5 kg and 6.8 kg. The fourth plot was marked along the field bund, and the labourers had also swept the grain from the bund edge into that plot's heap. Grain moisture measured with the office meter is 18 per cent, while yields are to be reported at 14 per cent moisture. The village-level worker says the field looked like it would give about 20 quintals per hectare and asks you to 'adjust' the figures so that the record matches the expectation. Reporting is due the same evening.
1. Convert each plot weight into kg per hectare and decide whether the fourth plot should be retained. Show the effect of your decision on the estimate.
Read the worked answer
Plot area = 5 m × 5 m = 25 m². Yield (kg/ha) = weight ÷ 25 × 10,000, i.e. weight × 400.
- Plot 1: 4.2 × 400 = 1,680 kg/ha
- Plot 2: 3.9 × 400 = 1,560 kg/ha
- Plot 3: 4.5 × 400 = 1,800 kg/ha
- Plot 4: 6.8 × 400 = 2,720 kg/ha
Plot 4 must be excluded. Its heap includes grain swept from the bund, and plants growing on the bund stand outside the 25 m² frame that was actually harvested. The weight therefore contains material produced outside the measured area - a classic edge effect - and it is not a measurement of the plot.
Effect on the estimate:
- Mean of the three valid plots = (1,680 + 1,560 + 1,800) ÷ 3 = 1,680 kg/ha
- Mean with plot 4 included = (1,680 + 1,560 + 1,800 + 2,720) ÷ 4 = 1,940 kg/ha
Including it inflates the estimate by 260 kg/ha, about 15.5 per cent - enough to distort a block-level wheat figure.
2. Apply the moisture correction and state the yield you will report.
Read the worked answer
Weights are reported at a standard 14 per cent moisture, but the meter read 18 per cent, so the grain carries extra water that must be netted out.
Corrected weight = field weight × (100 − 18) ÷ (100 − 14) = field weight × 82 ÷ 86 = field weight × 0.9535.
Corrected mean = 1,680 × 0.9535 = 1,601.9 kg/ha, i.e. about 1,602 kg/ha, or 16.0 quintals per hectare.
Because all three valid plots came from the same field and were measured at the same moisture, correcting the average gives the same result as correcting each plot and then averaging. If moisture had differed between plots, each plot would have to be corrected first and only then averaged.
Note also the scope: this is one field. The block estimate requires all crop-cutting plots, each weighted by the area it represents. The figure to enter is 1,602 kg/ha at 14 per cent moisture - the field-moisture weight of 1,680 must not be entered as the yield.
3. How do you answer the village-level worker, and what do you write in the record?
Read the worked answer
Refuse clearly, and make the refusal part of the record.
The worker's '20 quintals' is an impression, not a measurement. Shifting 1,602 to about 2,000 kg/ha to match it would be fabrication, and such a gap is exactly what a later re-check or audit looks for. Explain the two steps that produced the number - weighing from a measured 25 m² frame and the standard moisture correction - and show him the arithmetic. If he disputes the exclusion of plot 4, show him that the bund plants were outside the frame.
Record: plot dimensions, the four individual weights, the moisture reading and the meter used, the reason for rejecting plot 4, the name of the person who harvested and threshed, and the date. If a replacement plot is required, it must be drawn from the reserve list for the same field - never obtained by averaging the suspect weight into the result.
Report 1,602 kg/ha at 14 per cent moisture, with a footnote that one of four plots was rejected for bund harvest.