Haulm
The haulm consists of aerial and below soil level stems. The areal stems are in general hollow and triangular in cross section. The lower part of the stem is round and solid. The stolons and the roots grow on the below soil level stem parts.
Mature leaves are compound, consisting of a petiole with terminal leaflet, lateral leaflets, secondary leaflets and sometimes tertiary leaflets.
The foliage of the crop is the "carbohydrate factory". Green leaves intercept light and CO2 and water is converted in carbohydrates and water.
Indicators for light interception are: stem density, the morphological growth of the stem, LAI and percentage ground cover.
PHOTOSYNTHESIS & RESPIRATION
Stem density and crop density.
Crop density is either expressed as number of main stems per m2 or as the number of plants per hectare. As a rule of thumb: the density for a consumption potato crop is 15 - 20 main stems per m2 or 35 000 - 40 000 plants per HA .
A main stem is considered as a plant unit. From a seed 1, 2, 3, 4 or more main stems may develop and it is more accurate to express crop density as number of stems per hectare, than as number of plants per hectare. A stem is considered to be a main stem if it grows directly from the seed tuber. The lower lateral branches from the stem are called secondary stems. If a secondary branches off from the main stem, then this secondary stem may be considered as a main stem.
Mainstem and secondary stem
Morphological growth of the stem
Apart from lateral branching a potato stem may develop apical branches several times during its growth according to a certain pattern, while the lower (first leaves of the plant) drop from the plant or turn yellow. In fact during the production season the older leaves at the lower part of the plant are replaced by new leaves at the top of the stem.
Morphology haulmgrowth
During the first phases leave haulm growth is fast and later slower.
Haulm growth at various phases of growth
Consequently spraying schedules for late blight need to be adjusted to haulmgrowth.
SPRAYING SCHEDULES
Percentage ground cover
This is an important crop characteristic since it indicates what percentage of the incoming solar irradiation is used for photosynthesis.
Ground coverage with green leaves---Ground coverage with green leaves
Leaf area index-LAI
Leaf area index-LAI is the ratio of leaf surface over soil surface.
LEAF AREA INDEX