Punjab in Pakistan is the major food producing province and titled “bread basket” for the country’s more than 220 million people. Wheat is the major cereal crop produced in Punjab, putting Pakistan 8th among the wheat producing countries. Estimation of wheat area and production before harvest is important input for key operational decision making on post-harvest crop marketing and ensuring food security of dependent populations. Ahmad Khan [Faculty Assistant] from UMD’s Global Land Assessment and Discovery (GLAD) team has been working on the characterization of wheat crop in Punjab and has developed a turn-key operational model capable of producing pre-harvest wheat area. To take it further, and estimate wheat yield and production, the GLAD team has conducted its first field campaign under the NASA’s funded Harvest Consortium at the University of Maryland, Department of Geographical Sciences.
In collaboration with the Crop Reporting Service of Punjab, Ahmad Khan led the field campaign this year, with research extending over two months. This was a three-stage simple random sampling of the Punjab province with 25 sample blocks of 5 km x 5 km randomly selected in the first stage. From each of these sample blocks, 10 pixels were then randomly selected and from each of the sample pixels, a variable number of 2 m x 2 m crop cuts were selected. The number of crop cuts was based on proportion of wheat cover in a pixel assessed in the field, ranging from 0 for no wheat cover to 5 for a sample pixel fully covered with wheat.
The field sampling was composed of two campaigns, the first being identification of the sample pixels and assessment of the crop cuts with delineation of each crop cut. The second campaign was collection of wheat from each of the delineated crop cuts, separating grain from the wheat kernel collected from each of the sample pixels, and weighing the grain to obtain average wheat produced per sample pixel. Analysis of the field data suggests that the estimate of 20.04 million tonnes for Punjab is about 3% higher than the estimate of the Crop Reporting Service of Punjab, i.e. 19.37 million tonnes. Using multi-year field data as a calibration input, the GLAD team will next develop a Landsat based model to estimate wheat yield and production for Punjab. The field samples will be reference for accuracy measures of the Landsat-based model.
Preliminary results of the field data show that this sampling - which is simpler in application, easier logistically, and quicker in implementation - can provide wheat yield estimates that are comparable to the official statistics. The University of Maryland based NASA Harvest and GLAD programs have been able to leverage their collaborative relationship in order to promote the development of new techniques in an effort to increase the accessibility of vital crop information.
*This article was adapted from the original posting at nasaharvest.org*
