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Crop productivity (or yield) is a measure of the total sum of annual plant production, which is also known as net primary productivity. Crop productivity can be partitioned by tissue type (grain, leaves, stems, etc.) based on how the plant is used. The unused portions of crops are often referred to as crop residues, which is the next indicator.
Metrics by level
The inference zone is important to consider for all crop productivity metrics. On-farm measurements, and farmer qualitative data may be influenced by local conditions and culture, thus extrapolation from this information needs to be carefully considered.
The quality of production is often important and this can be difficult to account for in a quantitative measure of kilograms per hectare. One approach is to compare production for similar quality of product from the same species (for example, dividing potato production into market grades). Fodder quality assessment is described in the “Crop residue productivity” section below.
Relative differences in productivity are even more complex to measure when multiple crops are produced on the same field. In some cases, the production of all crops can be compared in terms of the monetary value of production (which relates to income, an indicator in the economic domain) or their nutritional value (calories, protein, etc.), which is an indicator in the human condition domain. More often it is necessary to report production separately for each of the different types of plants. Productivity of intercropping is typically compared to monocropping through a calculation known as the land equivalent ratio (Mead and Willey, 1980):
Where Ya is the intercropped yield of crop A, Sa is the sole crop yield of crop A, Yb is the intercropped yield of crop B and Sb is the sole crop yield of crop B. A LER of 1.2 means that it would take 1.2 hectares of sole crops to produce the same amount as 1 hectare of the intercrops.