Nitrogen uptake and utilization in sunflower and potato intercropping

Abstract: Intercropping not only improves crop yield and resource use efficiency, but also reduces soil-wind erosion as a biological hedge in winter periods. It is important to quantify the mechanism of nitrogen competition and affiliation, thereby to enhance nitrogen use efficiency and agricultural sustainability. We explored nitrogen uptake and utilization in sunflower and potato intercropping systems by field experiments, which were carried out in 2010 and 2011 in Wuchuan, Inner Mongolia. The plant nitrogen content for different organs and nitrogen uptake was measured by using the Semi-micro Kjeldahl method. The results showed that the sunflower and potato intercropping systems did not significantly improve crop nitrogen uptake comparing to the monocultures at system level. The nitrogen equivalent ratios (NER) for uptake ranged from 0.95 to 1.02, and were not significantly different between intercropping configurations. At crop level, intercropping did not reduce nitrogen uptake and utilization efficiency of sunflowers, but reduced that of the potato. Intercropped sunflowers showed a significant advantage in nitrogen competition and uptake, in which the partial NER, ranged from 0.53 to 0.74, was higher than its relative density (50%), while the intercropped potato showed a significant disadvantage, which the partial NER (ranged from 0.28 to 0.42) was much lower than its relative density (50%). Nitrogen physiological use efficiency (NPE) yield produced per unit N uptake of intercropped potato (fresh tuber weight with 80% water content) was 249.2 g/g, slightly lower than that of the sole system (269.8 g/g). In a four rows of potato and four rows of sunflower (4P:4S) intercropping system, the NPE of intercropped potato was 238.2 g/g, significantly decreased compared to that of the sole potato. The NPE of sunflower (grain with 12% water content) in 4P:4S intercropping (30.1 g/g) was 16.2% greater than that of the sole sunflower (25.9 g/g), also higher than that in two rows potato and two rows sunflower (2P:2S) intercropping (22.8 g/g). The NPE of 4P:4S intercropped sunflower increased at the expense of decreasing NPE of potato. The harvest index (HI) of intercropped potato (0.83) was lower than that of the monoculture (0.87); however, the HI of intercropped sunflower (0.40) was significantly higher than that of sole sunflower (0.33). The change of crop NPE was mainly affected by the crop harvest index.