Effects of crop rotation and fertilizer application on aboveground biomass and soil organic C in semi-arid region

Chinese. 了解轮作与施肥对土壤有机碳的影响是建立持续发展措施的关键。以长期定位试验（1984～2002）中的10个典型处理为基础，分析了地上部生物量和耕层（0～20 cm）土壤有机碳变化，探讨半干旱区轮作和施肥对0～20 cm土层有机碳的影响，10个典型处理分别为休闲（F）；冬小麦连作体系中的3个施肥处理：不施肥（W/W+CK）、化肥（W/W+NP）、化肥有机肥（W/W+NP-FYM）；冬小麦-冬小麦+糜子-豌豆轮作体系中的3个施肥处理：不施肥（W/WM/P +CK）、化肥（W/WM/P +NP）、化肥有机肥（W/WM/P+NP-FYM）处理；1个冬小麦―冬小麦-红豆草轮作处理（W/W/S+NP）；人工苜蓿中2个施肥处理：不施肥（A/A+CK）和化肥有机肥处理（A/A+NP-FYM）。冬小麦连作体系（W/W）中，不施肥处理（W/W+CK）的地上部生物量平均为3.3 t•ha-1，化肥处理（W/W+NP）和化肥有机肥处理（W/W+NP-FYM）依次为7.5和11.2 t•ha-1；冬小麦-冬小麦+糜子-豌豆轮作（W/WM/P）体系中，不施肥处理（W/WM/P+CK）地上部生物量平均3.1 t•ha-1，W/WM/P+NP和W/WM/P＋NP-FYM地上部生物量依次为7.1和8.3 t•ha-1；冬小麦-冬小麦-红豆草轮作（W/W/S+NP）为8.5 t•ha-1；苜蓿连作不施肥（A/A +CK）和化肥有机肥处理（A/A+NP-FYM）体系地上部生物量依次为4.1和5.0 t•ha-1。18年期间， W/W+CK处理土壤有机碳含量（6.7 g•kg-1）无显著变化，W/W+NP和W/W+NP-FYM处理提高13%和51%； W/WM/P+CK土壤有机碳含量（7.0 g•kg-1）无显著变化，W/WM/P+NP和W/WM/P＋NP-FYM土壤有机碳提高7%和47%；W/W/S+NP处理土壤有机碳提高了29%；A/A+CK和A/A+NP-FYM处理有机碳提高了43%和71%。轮作与施肥显著影响土壤碳输入量，18年期间土壤蓄存的碳与累计输入土壤的有机碳存在显著的线性相关关系（SOC=1.65CReturned+5.95，R2＝0.95＊＊）。秸秆还田、草粮轮作或退耕还草是改善该地区土壤质量，实现土壤蓄存碳潜力的重要途径。

English. A better understanding of crop rotation and fertilization on soil organic C(SOC) in cropping soils is vital for development of effective agricultural practices. Changes in soil organic C (0-20 cm) and aboveground biomass from 1984 to 2002 were investigated in ten cropping systems in a long-term field experiment started from 1984 on the Loess Plateau. The ten cropping systems consist of fallow (F), continuous winter wheat cropping system (W/W+CK, W/W+NP, and W/W+NP-FYM), wheat-wheat+millet-pea rotation system (W/WM/P+CK, W/WM/P+NP, and W/WM/P+NP-FYM), wheat-wheat- sainfoin (Onobrychis viciaefolia) (W/W/S+NP), and continuous alfalfa continuous(A/A+CK, A/A+NP-FYM). For the continuous winter wheat cropping system (W/W), the above ground biomass without fertilization (W/W+CK) was 3.3 t•ha-1, the above ground biomass in W/W+NP and W/W+NP-FYM was 2.2 and 3.4 times that in W/W+CK. For the wheat-wheat+millet-pea rotation system (W/WM/P), the above ground biomass without fertilization (W/WM/P+CK) was 3.1 t•ha-1, the above ground biomass in W/WM /P +NP and W/WM /P+NP-FYM was 2.3 and 2.7 times that in W/W+CK. The above ground biomass in W/W/S+NP, A/A +CK, and A/A +NP-FYM was 8.5, 4.1, and 5.0 t•ha-1, respectively. After 18 years SOC in W/W+CK (6.7 g•kg-1) was near to the value (6.5 g•kg-1) at the beginning of the experiment, increased by 13% and 51% in W/W+NP and W/W+NP-FYM, respectively. SOC in W/WM /P +CK was 7.0 g•kg-1, increased by 7% and 47% in W/WM/P +NP and W/WM/P+NP-FYM, respectively. SOC in W/W/S+NP, A/A +CK, and A/A +NP-FYM increased by 29%, 43% and 71%, respectively. The amount of returned C to soil plays an important role in SOC in the semi-arid region. There was a highly significant correlation between SOC and soil total N (SOC=1.65CReturned+5.95，R2＝0.95＊＊). Incorporation of crop straw into soil, crop rotation with grass, and conversion of cultivated land into grassland could promote SOC accumulation and sequestration of CO2 in farmlands in the semi-arid region.