Methods of crop yield measurement on multi-cropped plots: Examples from Tanzania

Abstract

Precise agricultural statistics are necessary to track productivity and design sound agricultural policies. Yet, in settings where multi-cropping is prevalent, even crop yield-perhaps the most common productivity metric-can be challenging to measure. In a survey of the literature on crop yield in low-income settings, we find that scholars specify how they estimate the area denominator used to measure yield in under 10% of cases. Using household survey data from Tanzania, we consider four alternative methods of allocating land area on multi-cropped plots, ranging from treatment of the entire plot as the yield denominator to increasingly precise approaches that account for the space taken up by other crops. We then explore the implications of this measurement decision for analyses of yield, focusing on one staple crop that is often grown on its own (rice) and one that is frequently found on mixed plots and in intercropped arrangements (maize). A majority (64%) of cultivated plots contain more than one crop, and average yield estimates vary with different methods of calculating area plantedparticularly for maize. Importantly, the choice among area methods influences which of these two crops is found to be more calorie-productive per hectare. This choice also influences the statistically significant correlates of crop yield, such that the benefits of intercropping and including legumes on a maize plot are only evident when using an area measure that accounts for mixed cropping arrangements. We conclude that the literature would benefit from greater clarity regarding how yield is measured across studies.

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“…The nutrient yield per ha for each crop was then averaged to obtain the nutrient yield per ha for PD and PI crops. This approach is similar to studies that convert yield to nutrient per ha to understand a crop’s nutrient yield and contribution 39 , 40 . For example, Cassidy et al 40 used this approach to get the average yield per ha for multi-cropped plots by converting the yield to nutrient per ha in Tanzania.…”

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“…The bene ts of mixed cropping (which also includes intercropping) are dependent on the speci c intercropping arrangement and include risk reduction to climate variation or disease, labour constraints, maximal utilization of limited space etc. (Wineman et al 2019). Mixed cropping may take on different spatial and/ or temporal arrangements, for example: one crop may occupy space within the plot that would otherwise be occupied by another; one crop may be added between rows of another crop which has been planted at its normal density; or two crops may share a plot for only a brief part of the growing season or occupy it at entirely different times of the year (Casley and Kumar 1989;Diskin 1997).…”

“…Mixed cropping may take on different spatial and/ or temporal arrangements, for example: one crop may occupy space within the plot that would otherwise be occupied by another; one crop may be added between rows of another crop which has been planted at its normal density; or two crops may share a plot for only a brief part of the growing season or occupy it at entirely different times of the year (Casley and Kumar 1989;Diskin 1997). In some cases, a particular crop is planted in more than one type of cropping system, for example pure stand and mixed cropped or multiple mixed cropping patterns (Murphy et al 1991;Wineman et al 2019).…”