氮肥施用量对不同紫甘薯品种产量和氮素效率的影响

选取紫甘薯品种浙紫1号、宁紫2号和紫菁2号，设置3个施氮处理，即0 (N0)、75 (N1)和150 (N2) kg hm^–2纯氮，于2013-2014年2个生长季在青岛农业大学现代农业科技示范园进行大田试验，研究不同氮肥用量对块根产量、干物质累积速率、氮素累积量及氮素效率的影响。结果表明，施用氮肥不同程度地降低了浙紫1号和紫菁2号的薯块产量，其中，浙紫1号的N1、N2处理分别较N0处理降低12.64%和13.32%，紫菁2号分别降低3.94%和29.06%；宁紫2号N1处理产量略高于N0处理，两年分别较N0处理提高8.5%和3.4%，而N2处理块根产量显著低于N0处理。茎蔓生物量和氮素累积量随着施氮量的增加而增加，而收获指数、氮素收获指数和氮素利用效率逐渐降低。第1年N1、N2处理的茎蔓干物质累积量分别较N0处理提高2.7%~20%和12.3%~36.4%，第2年分别提高12.6%~51.9%和28.7%~85.5%。相关分析表明，块根产量与氮素效率各指标均呈显著或极显著正相关；而茎蔓生物量与收获指数、氮素收获指数及氮肥利用效率均呈极显著负相关(r = –0.615^**, –0.704^**, –0.663^**)。肥沃土壤上施用氮肥会造成浙紫1号和紫菁2号的茎蔓旺长，光合产物向薯块转运比例降低，导致源库比例不协调，块根产量下降。宁紫2号对氮肥的需求相对较高，施用氮肥75 kg hm^–2时鲜薯产量提高，而施氮量过高时薯块产量降低。因此，紫甘薯在含氮量较高的肥沃土壤上种植时，对氮肥的需求量较低，茎蔓和薯块的协调生长是提高块根产量和氮素利用效率的保障。

Effects of Nitrogen Application Rates on Root Yield and Nitrogen Utilization in Different Purple Sweetpotato Varieties

A two-year field experiment was conducted in the Modern Agricultural Science and Technology Demonstration Garden of Qingdao Agricultural University in 2013 and 2014. Three varieties of purple sweetpotato (Zhezi 1, Ningzi 2, and Zijing 2) were grown with three nitrogen rates (0, 75, and 150 kg·ha^–1 as N0, N1, N2 treatment, respectively). The storage root yield, dry matter accumulation rate, nitrogen accumulation amount and N use efficiency of the purple sweetpotato were investigated under the three N levels. The results showed that the storage root yields of Zhezi 1 and Zijing 2 in N1 and N2 treatments reduced to a varying degree compared with N0 treatment, with the decrease of 12.64% and 13.32% for Zhezi 1 and 3.94% and 29.06% for Zijing 2, respectively. Meanwhile, the storage root yield of Ningzi 2 in N1 treatment slightly increased by 8.5% and 3.4% in 2013 and 2014, respectively, compared with N0 treatment, but significantly decreased in N2 treatment compared with both N0 and N1 treatments. Compared with N0 treatment, the shoot biomass increased from 2.7% to 20% in N1 and from 12.3% to 36.4% in N2, in 2013, as well as from 12.6% to 51.9% in N1 and from 28.7% to 85.5% in N2, in 2014. However, the harvest index, N harvest index and nitrogen use efficiency gradually reduced with the increase N application. The correlation analysis showed that the root yield positively correlated with all the nitrogen efficiency parameters, however the shoot biomass negatively correlated with the harvest index, nitrogen harvest index and nitrogen utilization efficiency (r = 0.615^**, 0.704^**, 0.663^**). The shoot biomass of Zhezi 1 and Zijing 2 increased with the increase of N application, showing the decrease of photosynthate from shoots to roots. The nitrogen demand of Ningzi 2 was higher than other two varieties, and the moderate nitrogen application could increase the root yield in fertile soil. In conclusion, the coordinated growth of shoots and roots is important for improving storage root yield and N use efficiency.