Independent research has demonstrated the particular importance of phosphorus for tuber bulking. The longer the phosphorus level in the crop is maintained at a high level the greater the yield potential. Yield potential is increased by around 0.5 t/ha for each extra day that the phosphorus level in the petiole is kept above 0.22%. However the level of phosphorus in the petiole peaks at tuber initiation and then declines as the season progresses. In northern European conditions the phosphorus level normally arrives at 0.22% around 100 to 110 days after planting. Any “premature deficiency” incurs a yield penalty of 0.5 tonne per hectare per day.
If prediction of the phosphate requirement can be made early in the season then the 0.5 tonnes per hectare per day through the bulking phase can be saved - or gained. Yara has the answer in its petiole analysis databank and range of effective foliar phosphates
Since 1993 we have been analysing petiole samples from UK potato crops and our database currently stands at over 5,000 samples and continues to rise. Biometric analysis of results allows us to establish phosphorus values early in the season which are equivalent to the critical figure of 0.22% at 100 days after planting.
The Yara petiole Megalab system is proactive because when a petiole sample is analysed we are asking the question “Will this crop make it to 100 days after planting before the phosphorus level drops below 0.22%?”.Another benefit is that normally only one sample per season is needed, however, if extremes of weather occur, a further petiole sample 3-4 weeks later will highlight any adverse trends.
Similar trends exist for the other important nutrients for the potato crop. So using Megalab means that yield potential is not limited by reduced levels of major, secondary or micro nutrients.
Choose the youngest fully expanded leaf (usually 4th) at a stage no earlier than 10% flowering. For each complete leaf, separate the leaflets from the petiole, and discard the leaflets as soon as possible after sampling. Keep samples in a cool dark place, and send to the lab immediately.
Draw from at least 20 different locations in the field. At each location take one leaf branch from each of 3-4 plants (minimum of 60-80 branches in total). Do not sample fields within 3-5 days after being sprayed with pesticides or foliar nutrients.
View or download the Potato Petiole Analysis Technical Bulletin as a PDF.