半干旱黄土丘陵区施肥对退耕地紫花苜蓿生物量的影响

为了提高退耕地紫花苜蓿的地上生物量并延缓其衰败期,对定西安定区龙滩流域退耕地播种5年后的紫花苜蓿,于2007-2008年连续2年开展氮肥和磷肥混合撒施施肥试验。结果表明,施N肥对促进苜蓿生长并提高生物量没有明显的效果,施P肥效果明显,2年的施肥苜蓿平均生物量分别是对照的1.62和1.15倍,可显著促进苜蓿生长并提高其生物量,其中P肥最大用量为12 kg/667 m²时的生物量最高。栽培第7年的苜蓿鲜草产量平均可达18 240 kg/hm²。研究区阳坡的苜蓿比阴坡的苜蓿生长好、生物量高,其鲜草和干草平均生物量是阴坡的1.49和1.43倍。在年降水量400 mm左右的半干旱黄土区,苜蓿产量主要由第1茬苜蓿产生,约占全年总产量的75％,第2茬苜蓿产量较小,约占总产量的25％,所以在该区域苜蓿1年适宜收割2次。

Effect of fertilization on biomass of alfalfa in returned farmland in semiarid loess hilly area

For increasing the aboveground biomass of alfalfa (Medicago sativa) in returned farmland and prolonging its degradation time, the mixed fertilization experiment of nitrogen and phosphate fertilizer was conducted two times in 2007-2008, on alfalfa grassland that has been planted for five years in Longtan catchment, Anding district, Dingxi city. The result showed that nitrogen fertilizer has no obvious effect on increasing the growth conditions and biomass of alfalfa. However, phosphate fertilizer has significant influence on promoting the alfalfa’s growth and increasing biomass. And the mean biomass of fertilized alfalfa in 2007 and 2008 was 1.62 and 1.15 times the biomass of control alfalfa respectively. The highest biomass of alfalfa was appeared when phosphate fertilizer rate was highest of 12 kg/667 m². The mean fresh biomass of alfalfa can achieve 18 240 kg/ha on seventh year. The growth conditions and biomass of alfalfa on sunny-slopes was better than that on shady-slopes,and its mean fresh and dry biomass were 1.49 and 1.43 times the biomass of shady-slopes respectively. In the semiarid loess area with 400 mm annual precipitation, the biomass of alfalfa harvest was mainly produced by the 1st harvest and it accounted for about 75% of annual biomass, whereas the biomass of 2nd harvest was small and accounted for about 25%. So twice per year for alfalfa harvest is optimized in this area.