Nitrogen and phosphorus leaching losses from potatoes with different harvest times and following crops

A 3-year field study (2007–2009) was conducted in separately tile-drained plots on a sandy soil in south-west Sweden to determine nitrogen (N) and phosphorus (P) leaching losses from potatoes to the drainage system. Different types of potatoes were grown and harvested at different times followed by different crops in order to identify the potato type/following crop system with the lowest risk of N and P leaching losses. Accumulated annual amounts of N and P lost to drainage between May (potato planting) and the following April varied between 13 and 72 kg N ha−1 and 0.04 and 0.24 kg P ha−1 depending on treatment and year. P leaching losses from this particular soil were low and differences between potato types not distinct, but there were significant differences between years. Abnormally high precipitation in summer 2007 led to significantly higher P leaching losses than in other years. N leaching losses were also higher in 2007, but differences between potato types were found in all years. Despite the high mineral soil nitrogen content (Nmin) after harvest in June, early potatoes (EP) with oilseed radish (oil) as catch crop showed the lowest N leaching losses of all potatoes. Potatoes harvested in August (table potato; TP) and September/October (late potato; LP) followed by triticale (tri) sown in October showed the highest leaching losses. Thus under current climate conditions in Sweden, oilseed radish after EP is a suitable catch crop for N, while triticale sown in October is ineffective in preventing N leaching after potatoes. The late harvest of starch potatoes (SP) did not allow establishment of a following crop. However, SP showed lower N leaching losses than TP + tri and LP + tri due to lower residual Nmin in deeper soil layers, low temperatures after harvest decreasing soil N mineralisation and higher C:N ratio of the potato haulm leading to lower N mineralisation potential. As a mean of all years, N leaching losses during and after EP + oil and SP were similar to those from the reference crop spring barley (SB), whereas TP + tri and LP + tri require countermeasures against N leaching.

► N and P leaching losses were measured from potato crops destined to different markets.
► P leaching from potatoes was negligible, but N leaching high.
► Lowest N leaching for starch potatoes and early harvested potatoes with catch crop oilseed radish.
► Highest N leaching for storage potatoes harvested September/October.
► Winter cereals not suitable as catch crops for N after storage potatoes.