中国北方甜菜土壤速效钾丰缺指标与适宜施钾量研究

为了给甜菜测土施肥提供科学依据,采用零散实验数据整合法、缺素处理相对产量与土壤养分含量回归方程法和“养分平衡—地力差减法”确定适宜施肥量新应用公式,开展了我国北方甜菜土壤速效钾丰缺指标与适宜施钾量研究。结果表明,中国北方甜菜土壤速效钾(NH4OAc-K)第1~5级丰缺指标依次为>409、224~409、123~224、68~123和≤68 mg/kg。当钾肥当季利用率40%、目标产量30~90 t/hm^2时,土壤速效钾丰缺级别第1~5级的适宜施钾量范围依次为0~0、41~124、83~248、124~371和165~495 kg/hm^2。     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK: 6. The effect of reducing stocking rate and application of fertilizer nitrogen in Wales

Abstract The implications for the agricultural productivity of the UK upland sheep systems of reducing nitrogen fertilizer application and lowering stocking rates on perennial ryegrass/white clover swards were studied over 4 years at a site in Wales. The system involved grazing ewes and lambs from birth to weaning on swards maintained at a constant height with surplus herbage made into silage, thereafter ewes and weaned lambs grazed on separate areas until the onset of winter with adjustments to the size of the areas grazed and utilizing surplus pasture areas for silage. Four stocking rates [SR 18, 15, 12 and 9 ewes ha^?1 on the total area (grazed and ensiled)] and two levels of annual nitrogen fertilizer application (N 200 and 50 kg ha^?1) were studied in five treatments (N200/SR18, N200/SR15, N50/SR15, N50/SR12 and N50/SR9). Average white clover content was negatively correlated with the level of annual nitrogen fertilizer application. White clover content of the swards was maintained over the duration of the experiment with an increasing proportion of clover in the swards receiving 50 kg N ha^?1. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain from birth to weaning in all treatments but fewer lambs reached the slaughter live weight by September at the higher stocking rates and with the lower level of fertilizer application. Three of the five treatments provided adequate winter fodder as silage (N200/SR15, N50/SR12 and N50/SR9). Because of the failure to make adequate winter fodder and the failure of white clover to fully compensate for reduction in nitrogen fertilizer application, it is concluded that nitrogen fertilizer can only be reduced on upland sheep pastures if accompanied by reduced stocking rates.