不同间作播期和密度对甜瓜/向日葵间作系统氮素利用效率的影响

在大田条件下以甜瓜和向日葵为试材,研究两种作物单作和向日葵间作播期(甜瓜伸蔓期、开花坐果期、果实膨大期)、间作密度高(24 975株·hm~(-2))、中(22 200株·hm~(-2))和低(19 980株·hm~(-2))]对间作系统和两种作物单作的氮素积累量、氮素利用效率和光能利用效率的影响。结果表明,间作显著提高了间作系统甜瓜的氮素累积和利用效率,却降低了向日葵的氮素累积和利用效率。间作甜瓜植株地上部的氮素累积量平均为195.08 kg·hm~(-2),较单作甜瓜(172.61 kg·hm~(-2))提高13.0%,氮素利用效率和氮肥偏生产力均显著高于单作(分别提高40.5%和55.4%)。间作系统向日葵氮素利用效率和氮肥偏生产力较单作降低8.2%和58.4%,而氮素收获指数较单作提高4.9%。在甜瓜伸蔓期、开花坐果期和果实膨大期间作向日葵,间作系统的氮素利用效率较同播期的单作向日葵分别提高43.5%、12.5%和59.8%;果实膨大期间作向日葵,间作系统的氮素利用效率较单作甜瓜提高6.7%。在甜瓜伸蔓期、开花坐果期和果实膨大期间作向日葵,间作系统的氮肥偏生产力较同播期的单作向日葵提高6.5%、32.1%和40.4%,较单作甜瓜分别降低22.5%、10.1%和34.3%;在甜瓜伸蔓期、开花坐果期和果实膨大期间作向日葵,间作系统的氮素收获指数较同播期的单作向日葵分别降低7.2%、7.7%和12.5%。高、中和低3个间作密度下,间作系统的氮素利用效率较同密度甜瓜单作分别降低14.2%、20.4%和13.9%,较向日葵单作分别提高25.2%、20.0%和9.5%,氮肥偏生产力较同密度甜瓜单作降低29.6%、15.6%和21.1%;高密度和低密度间作处理的间作系统氮素收获指数较向日葵单作提高2.7%和1.4%,而中密度间作降低7.6%。间作系统甜瓜的光能利用效率与氮素利用效率呈显著正相关关系,向日葵的光能利用效率与氮素利用效率无显著相关。在河西绿洲灌溉条件下,氮素利用率较高的适宜向日葵间作播期为甜瓜果实膨大期,适宜间作株距为40 cm(密度为24 975株·hm~(-2))。

Effects of intercropping time and planting density on nitrogen use efficiencyof melon-sunflower intercropping system

A field experiment comprising of monoculture and intercropping of two crops (melon and sunflower) was conducted at three sunflower sowing times (at vine running, flowering and fruit expansion stages of melon) at three intercropping densities of each crop high (24 975 plant·hm^-2), medium (22 200 plant·hm^-2) and low (19 980 plant·hm^-2)] to study plant nitrogen accumulation and nitrogen use efficiency and to determine the relationship between solar energy utilization efficiency and nitrogen use efficiency. The results showed that intercropping significantly increased nitrogen accumulation and nitrogen use efficiency of melon, but reduced those of the sunflower. Under intercropping conditions, nitrogen accumulation of above-ground parts of melon was 195.08 kg·hm^-2, increasing by 13.0% compared with that of monocultured melon (172.61 kg·hm^-2). Nitrogen use efficiency and partial nitrogen productivity of intercropped melon significantly increased, respectively, by 40.5% and 55.4%, over those of monocultured melon. Nitrogen use efficiency and nitrogen partial productivity of sunflower under intercropping decreased, respectively, by 8.2% and 58.4% compared with those of monocultured sunflower, but nitrogen harvest index increased by 4.9%. Nitrogen use efficiency of intercropping system at three sunflower intercropping times (vine running, flowering and fruit expansion stages of melon) increased, respectively, by 43.5%, 12.5% and 59.8% over that of monoculture sunflower of the same sowing times. Also nitrogen use efficiency of intercropping system intercropped at fruit expansion period of melon increased by 6.7%, compared with average nitrogen use efficiency of monocultured melon. Partial nitrogen productivity of intercropped system with three intercropping times increased, respectively, by 6.5%, 32.1% and 40.4% compared with monocultured sunflower of the same sowing time, but decreased, respectively, by 22.5%, 10.1% and 34.3% compared with the average value for monoculturd melon. Nitrogen harvest index of intercropping system at three sunflower intercropping times decreased by 7.2%, 7.7% and 12.5%, respectively, compared with that of monocultured sunflower. Nitrogen utilization efficiencies of intercropping system at three intercropping densities reduced by 14.2% (high density), 20.4% (middle density) and 13.9% (low density), respectively, compared with that of monocultured melon at the same corresponding density, but increased, respectively, by 25.2%, 20.0% and 9.5% compared with the average value of monocultured sunflower. Partial nitrogen productivity of intercropping system with three intercropping densities decreased, respectively, by 29.6%, 15.6% and 21.1% compared with the corresponding treatments of monocultured melon. Nitrogen harvest index of intercropping system at high and low intercropping densities increased, respectively, by 2.7% and 1.4% compared with average nitrogen harvest index of monocultured sunflower, but decreased by 7.6% at medium density. There was significantly positive correlation between nitrogen use efficiency and light use efficiency of melon under intercropping system, but not with sunflower. The results suggested that fruit expansion period of melon was the most suitable intercropping time of sunflower and 40 cm plant spacing was the optimum planting density in melon-sunflower intercropping system, which resulting in high nitrogen use efficiency.