Measures of crop yield are important indicators of productivity and also provide a basis for assessing whether a landscape is supporting the livelihoods of the individuals who farm the land.
Measuring crop yield
Crop yield commonly is measured in kilograms per hectare (kg/ha). Often this standard weight per area measure is converted from a volumetric unit of measurement that is based on a commonly used container. Standard methods for measuring crop yield involve weighing a complete harvest or relying on expert judgement. These methods can be expensive however, requiring specialists and/or substantial labor and supervision. The following two methods are more economical and provide a reasonably accurate assessment of crop yield:
- Harvesting (crop cutting): A random sample of the crop in a particular field is cut and weighed. The total yield is calculated from the weight multiplied by the total acreage in production.
- Farmer estimation: Farmers are asked for their estimation of the total crop harvested. This value is divided by how much land they planted in order to estimate yield. This method has been found to be reasonbly accurate in determining annual or seasonal crop yields, but is not effective for continuous crops.
The frequency of measuring crop yield depends upon the crop. For seasonal crops such as maize, rice, and wheat yield is measured at the end of the cropping season when the crop is harvested. For a continuous crop such as tea, sampling should occur at least twice a year as the seasons vary, in order to get both a dry and wet season estimate to average across the year. More frequent sampling may be needed to capture seasonal variation across the year.
The Agricultural Productivity Indicators Measurement Guide by Patrick Diskin explores issues in crop measurement and interpretation of data, including choices in data collection methods and exogenous factors affecting crop yield. It describes in detail six indicators of agricultural crop production (e.g. harvested crop yield per hectare; percent crop loss during storage, others). It also outlines a plan for data collection for these indicators and provides concrete information on calculating values for them.
A paper analyzing the effects of smallholder commercialization of food crop input use and productivity in Kenya provides insight into mechanisms for increasing food crop productivity.