1. PET- Crops

1.1 The PET- Crops protocol to estimate crop performance through identifying yields at harvest time comprises the structured application of increasing intensities of observation, best described diagrammatically as an inverted pyramid as shown in Figure 1, beginning with observations from a vehicle, then walking and finally made within fields during discussions with farmers.

Figure 1. Observation Levels

2. Vehicle Transects

2.1 At the first level, observers identify the approximate yield of all fields seen through the windshield of a vehicle travelling at a slow, steady speed. At such a distance and using the photo-indicators (annotated PET photos) of the fields from-a-distance, on the appropriate page in the manual for the crop in question, the proportion of harvestable crops passed on the journey that fit into the 3 categories, BLUE (low), YELLOW (medium) or RED (high) are identified.

2.2 The 3 colour categories have been established to ease rapid approximation of yields during transects. Indeed the range of yields should be regarded as contiguous - NOT as three pre-set isolated discontinuous clusters into which all high, medium and low crops must fall. The colours provide a convenient initial grouping, but do not preclude assessments of levels between each band (i.e. red-yellow; or yellow-blue). Also in some years it is possible, although unlikely, that there may be no crops in the red band. In such a year, the highest crop may be found in the yellow band. Other years there may be no crops in the blue band, the lowest crops being found in the yellow band, again equally unlikely, but possible and  such instances will be recorded in the system.

2.3 Every small field, or each regular section of large fields passed during the journey (transect) is classified as blue, yellow or red on prepared sheets by noting single ticks in columns of boxes under the corresponding heading that may be added-up at the end of the transect to enable weighted average yields of each crop under assessment to be prepared.

3. Walking Transects

3.1 On arrival at a designated area, or, an area of specific interest as determined by the results of the inital observations, or at predefined regular intervals, observers leave the vehicle and switch to walking transects which enable the fields to be observed more closely and allow crops to be categorised at low, medium or high levels within the colour bands and at levels between, below or above the colour category already determined during the driving transect, allowing more accurate assessments of yield to be made using the more detailed annotations linked to the photographs of close-up (1 sq m) and photos of the harvested product of that 1 sq m.

3.2 When sufficient fields have been closely observed and scored during the walking transect, the sequence of actions is completed by conducting detailed case-studies of a small number of available farmers involving a) semi-structured interviews in his/her field using a common pre-tested/proven checklist, and b) taking representative samples of the field, threshing, winnowing and weighing the product to cross -check your ues of the photo-indicator.

3.3 At the end of each day, each team summarises the weighted returns for the vehicular and walking transects and prepares summary sheets from the completed interview check lists. Samples are re-bagged, stored safely ready for drying later to determine dry-matter content:and, the day's data cross-referenced to check for inconsistency.

PET Methodology - further details

Emphasis is placed on the facts that:-