The effect of preceding crop and pre-sprouting on crop growth, N use and tuber yield of maincrop potatoes for processing under conditions of N stress

Factorial field trials were carried out on an experimental farm near Kassel, Germany, in two consecutive seasons (2003 and 2004) in order to examine the impact of leguminous and cereal preceding crops (i) on soil N availability under subsequent potatoes and (ii) the effect of preceding crop and pre-sprouting of seed tubers on crop development, N uptake, N utilization efficiency and total and size-graded tuber yields relevant for processing into either crisps or French fries. In addition, an approach to analyse complex field experiments using mixed models is discussed. Soil mineralized nitrate-N at emergence of the potato crop was affected by the preceding crop and was highest when potatoes followed peas, while the short-term alfalfa/grass/clover ley appeared too sensitive to environmental conditions in the preceding cropping season, and its efficiency in terms of N supply may be hard to predict. Pre-sprouting advanced crop development and dry matter accumulation of the canopy, translocation of assimilates and N from canopy into tubers and allowed an increased N utilization efficiency. The positive effect of pre-sprouting on total tuber yield was compensated up to the final harvest, but a higher percentage of marketable tuber yield for French fries (> 50 mm) was found independently of the date of harvest. An increasing N supply (after peas and a following catch crop) may be efficient in terms of higher yields of the marketable size-grades (40-65 mm) for crisps, but increase oversized tuber yields in seasons not affected by Phytophthora infestans. Average tuber fresh weight responded consistently and positively to seed-tuber preparation (pre-sprouting), cultivar (cv. Agria) and an increased N supply (after peas).