Effects of continuous cropping on potato eco-physiological characteristics in the Yellow River irrigation area of the central Gansu Province

The Yellow River irrigation area in the central Gansu Province is one of the main potato growing regions in Northwest China. Potato is often grown continuously in a monocropping system by farmers and planting enterprises in Gansu to maximize consecutive payoffs. This practice has resulted in severe declines in tuber yield and quality. To address this problem, a field experiment was conducted in 2010 to study the effects of continuous potato monocropping (CPM) on eco-physiological characteristics of potato plant using the "Atlantic" potato variety in Jingtai County of Baiyin City. In the experiment, five treatments of continuous monocropping potato for 1~5 years were set, and named L1, L2, L3, L4 and L5, respectively. In addition, rotation treatment, in which maize was planted in 2008 and 2009, potato in 2010, was used as the control (L0). There was no statistical difference in tuber yield among L0, L1 and L2. However, significant declines in tuber yield occurred in L3, L4 and L5; decreasing by 44%~56% compared with L0. This proved that after continuing for two years, CPM significantly reduced tuber yield. For potato yield component, correlation analysis indicated that average fresh-weight of individual tuber was the leading cause of decline in tuber yield under CPM system. Dry matter contents of different potato organs gradually decreased with longer CPM duration. However, potato root-to-shoot ratio was the reverse. CPM significantly affected photosynthetic physiology of potato plants. While Pn, Gs and Tr significantly decreased with increasing CPM duration, Ci increased. CPM also significantly affected chlorophyll fluorescence parameters in potato leaf. Fv /Fm, ΦPSII and qP gradually increased with increasing CPM duration, whereas F0 gradually declined. There was a declining trend in the activities of SOD, POD and CAT in potato leaf after an initial increase with increasing CPM duration. There was no significant difference in potato leaf MDA content in L1 and L2 compared with that in L0. However, potato leaf MDA content increased about 4~6 folds respectively in L3, L4 and L5. The activity of potato root system, total root absorption area and root active absorption area all significantly declined with increasing CPM duration. Root morphological parameters including total root length, surface area and tip number gradually increased with increasing CPM duration, but were statistically not different in root diameter and volume among the six treatments. The results confirmed that CPM significantly affected not only the distribution of dry matter in potato plants, but also the changes in morphology and photosynthesis associated with physiologic processes of potato; causing tuber yield decline. Besides, the metabolism and regulation of endogenous hormones within potato plants were probably connected with the decline in tuber yield. This resulted in sink-source imbalance in potato plants.