Mineral N dynamic, N uptake and growth of lettuce as affected by mulch

In the years 1993 and 1994 lettuce cv. Prosper was cultivated at five different planting dates on the experimental farm of Hohenheim University, Germany. For each planting date mulch treatments were applied (black paper mulch, black polyethylene mulch, no mulch). Mineral N-content of soil (NO3-+NH4+) and plant growth were recorded weekly. There was no difference in the pattern of mineralization between mulch treatments but the maximum value of mineral N-content in soil and the time of appearence of maximum N-content differed. In treatment 'No mulch' we found the highest and earliest maximum for mineral N in soil. Under polyethylene mulch there was the lowest and latest maximum for mineral N in soil. The results of the treatment 'Paper mulch' were in-between the results of the other treatments. Effects of fertilizing and interactions between fertilizer and mulch treatment were much higher than effects of mulch treatment alone on mineral N-content in soil. We could not find differences in growth parameters of lettuce (head weight, root length) between mulch treatments. Root distribution was affected by mulch treatments.