摘要
从上世纪30年代以来,为了满足人们对农作物以及家畜对饲料的不断需求,加拿大大面积的草原被开垦种植一年生或多年生作物和牧草。长期以来,对于开垦天然草地种植牧草是否会提高草地生产力这个问题的研究经常得到不同的结论,而这些矛盾主要是由于实验时间、实验处理和实验设计不同造成的。本研究选取加拿大阿尔伯塔省南部具有代表性的两块从未被任何利用干扰过的天然草地作为实验样地对以上问题做了进一步研究。ADRI样地位于列桥市郊区(49°07′N,112°57′W),以针茅-格兰马草-冰草(Stipa– Bouteloua- Agropyron)建群,Onefour靠近阿尔伯塔省和美国的边境(49°03′N, 110°27′W),以针茅-格兰马草(Stipa-Bouteloua)建群。实验采用完全随机区组设计,7个处理,每个处理4次重复,地上净初级生产力每年测定一次,土壤采样在2006年4月份进行,并分为0-15cm、15-30cm、30-60cm和60-90cm四层。
研究结果表明:
1、各个耕作处理的地上净初级生产力和刈割净初级生产力显著受到样地以及样地、耕作处理和采样时间三者交互作用的影响(P<0.05)。ADRI样地中冰草在样地建立最初1-4年地上净初级生产力显著高于对照(P<0.05),但在接下来的5-13年中与对照趋于相等。但在Onefour样地的1-11年中地上净初级生产力均显著高于对照处理(P<0.05)。该结果说明在降水较少、温度较高的Onefour样地冰草是表现出较强的适应性和生长能力。两样地中小麦始终是最高产的作物,不论净初级生产力和刈割净初级生产力均显著高于对照处理。
2、开垦天然草地种植俄罗斯新麦草和冰草13或12年后,草地土壤碳氮含量、碳氮储量以及土壤轻组有机质性质与对照相比无显著变化(P>0.05),而种植小麦则使以上各个指标显著降低(P<0.05);所有耕作处理之间的土壤较稳定碳含量均无显著差异(P>0.05),土壤碳氮含量的变化主要来自于土壤易分解有机质库。
3、种植冰草使土壤碳氮矿化量显著增加而俄罗斯新麦草只造成土壤碳矿化的显著增加(P<0.05)。两个小麦处理使土壤矿化碳显著下降(P<0.05)而对矿化氮无影响(P>0.05)。
4、在加拿大普列里草原上,土壤碳氮、轻组有机质和土壤矿化碳之间存在显著或极显著相关关系(P=0.0001或P=0.05),而土壤矿化氮和硝化氮与以上指标无相关关系。地上净初级生产力与土壤碳氮含量呈一元一次线性正相关关系,而与土壤矿化碳、碳矿化速率、矿化氮、氮矿化速率、硝化氮和氮硝化速率呈一元一次线性负相关关系。
5、根系生物量受样地、耕作处理的影响(P<0.05)而不受样地和耕作处理交互作用影响(P>0.05)。俄罗斯新麦草的根系生物量显著高于对照,而两个小麦处理的根系生物量显著低于对照(P<0.05);ADRI样地所有处理的根系生物量均高于Onefour样地的根系生物量。
The production-oriented goals of agriculture have resulted in tremendous changes in land-use on the prairies with the conversion of native grassland to forage and crop land for food production and livestock fodder from 1930’s. The relative benefits of introducing forage species to the Northern Great Plains has been examined in well publicized studies with contradictory conclusion because of the differences by time of establishment, treatments arrangment and experimental design. Consequently, in order to clear the issue with trustable data and address a relative correct conclusion we prompted this study to re-examine the issue. Two experimental sites which were totally undisturbed on Mixed Prairie were selected in southern Alberta. ADRI is located in the suburb of Lethbridge(49°07′N, 112°57′W), near Animal Disease Research Institution with plant community of Stipa– Bouteloua- Agropyron. Onefour site is close to the boundry of Alberta and America(49°03′N, 110°27′W), with the plant community of Stipa-Bouteloua. The design of the field study was a randomized complete block design with 7 treatments, 4 replicates. ANPP was investigated every year. Soil samples were taken in fall 2006 at 4 increments (0– 15, 15– 30, 30– 60, and 60– 90 cm depth) for analysis.
The results showed:
1. ANPP and Ha-ANPP among forage types was influenced (P<0.05) by community and its interaction with treatment and sampling period. ANPP of ADRI was significantly higher than native grassland in 1 to 4 years after sites established(P<0.05) while tended to be similar with native grassland in the following 5 to 13 years. ANPP of Onefour was always significantly higher than naitve grassland in 1 to 11 years. The study confirmed the relative ANPP advantage of Crested wheatgrass on the Onefour site but not on ADRI site. Wheat was the most productive forage on both sites and its ANPP advantage to the native harvest appeared sustainable.
2. Converting native grassland to Russian wildrye and Crested wheatgrass 13/12 years had no effect on soil organic carbon and nitrogen concentration, soil organic carbon and nitrogen stock and light fraction qualities (P>0.05) while converting native grassland to Wheat led a lower soil organic carbon and nitrogen concentration, soil organic carbon and nitrogen stock and light fraction qualities less (P<0.05). All cropping treatments had no effect (P>0.05) on More stable carbon indicated the loss of soil carbon and nitrogen was mainly from labile organic matter pool.
3. Crested wheatgrass led a higher carbon and nitrogen mineralization (P<0.05) while while Russian wild rye only led a higher carbon mineralization than native grassland (P<0.05). Converting native grassland to wheat significantly lower (P<0.05) carbon mineralization while had no effect on nitrogen mineralization (P>0.05).
4. On the Mixed prairie, soil carbon and nitrogen stock, light fraction qualities, carbon mineralization and nitrogen mineralization were closely correlated to each other (P<0.05 or P<0.0001)while no relations between nitrogen mineralization and nitrificati was detected. ANPP positively liner related to soil organic carbon and nitrogen stock while negetive liner related to carbon nitrogen mineralization, nitrogen nitrification and their rates. No relations between ANPP and light fraction qualities were detected.
5. Corse root biomass was significantly effected by site and treatment (P<0.05) while was not effected by their interactions (P>0.05). Russian wild rye led higher corse root biomass than native grassland while wheat significantly lower corse root biomass (P<0.05). Corse root biomass on ADRI site was higher than Onefour site.
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