A touch more potash could lift pulses
PEAS and beans need a lot more soil potash than previously supposed, says the Potash Development Association.
According to the PDAs John Hollies, a re-examination of trials data from Rothamsted and Saxmundham, Suffolk, shows that for optimum yield, arable legumes require much more potash in the soil than the 120-180mg/litre currently indicated in the ministrys bulletin Fertiliser recommendations for Agricultural and Horticultural Crops RB209.
"It offers one explanation for the very large variations in the yield of field beans – the highest of any arable crop. There are huge differences in the application rates used. Growers on heavy soils often use nothing, others up to 180 units/acre."
Mr Hollies believes the current soil index system, with 100mg/litre representing the top end of index one, and 150mg/litre the bottom end of index two, hampers users in determining the best K dressing for their peas and beans. "Its too lumpy."
He claims the trials show yield responses for field beans at levels of up to 250mg/litre. But 85% of arable land has a concentration less than this.
Unlike cereals, legumes are poor scavengers and rarely receive the fillip of nitrogen which encourages potash uptake in other crops, he adds.
Light soils which do not hold potash well should be dressed annually. A new free leaflet outlining his arguments and giving recommendations is available from the PDA, Brixtarw, Laugharne, Camarthen SA33 4QP. *