Soil chemical attributes and energetic potential of agricultural residual biomasses provided by 23-year soil management

ABSTRACT Residual biomass from grains has potential as an energetic source. Biomass composition determines this potential and is related to plant nutrition, which may vary according to soil fertility. The aim of this 23-year field study was to evaluate changes in chemical attributes of a Brazilian Oxisol and in the energetic potential of oat (Avena sativa L.) and soybean (Glycine max (L.) Merr) residual biomasses provided by tillage systems and fertilizer rates. The trial was performed since 1989, assessing soil chemical attributes in no-tillage (NT), conventional (CT), minimum (MT) and no-tillage plus chisel plough (NT+CP), with two fertilizer rates (normal and reduced, since 1994). Oat and soybean (2012/2013) residual biomasses were collected and analyzed by its elemental composition, higher heating value (HHV) and theoretical potential for electricity production. The NT system presented higher P-resin availability; NT and NT+CP provided higher OM and total P content on soil surface. Without appropriate amounts of K and P fertilizer, P-resin and P total contents diminished mainly in 0-0.1 m depth, while exchangeable, non-exchangeable and total K+ fractions were mined even in deeper layers (0-0.3 m). The better general fertility conditions were achieved by conservative tillage systems, with normal fertilizer rate. Soil fertility levels changed chemical composition of both biomasses but had no effect on biomass HHV. Considering a system with oat and soybean grain production plus residual biomasses for energetic exploitation, it could be possible to generate 2,941 GWh·year–1, while still achieving 70% residue coverage under no-tillage maintenance.

摘要 谷物残余生物质具备作为能源原料的开发潜力。生物质组成决定了其能源化利用潜力，且与植物营养状况密切相关，而植物营养状况会随土壤肥力水平发生变化。本项为期23年的田间试验旨在评估巴西氧化土（Oxisol）的化学属性变化，以及不同耕作制度与施肥水平下燕麦（Avena sativa L.）和大豆（Glycine max (L.) Merr）残余生物质的能源化潜力。本试验自1989年起开展，对免耕（NT）、常规耕作（CT）、少耕（MT）以及免耕加凿式犁耕（NT+CP）四种耕作制度下的土壤化学属性进行监测；自1994年起设置常规施肥与减量施肥两个梯度。于2012/2013季采集燕麦与大豆残余生物质，对其元素组成、高位发热量（HHV）及理论发电潜力进行分析。免耕（NT）制度下树脂态磷（P-resin）的有效性更高；免耕（NT）与免耕加凿式犁耕（NT+CP）制度下土壤表层的有机质（OM）与全磷含量更为丰富。若未施加足量的钾（K）与磷（P）肥料，树脂态磷与全磷含量主要在0~0.1m土层中显著降低，而交换态钾、非交换态钾及全钾（K+）组分甚至在0~0.3m的深层土层中均出现耗竭。常规施肥水平下的保护性耕作制度可实现最优的综合土壤肥力状况。土壤肥力水平会改变两种残余生物质的化学组成，但对其高位发热量（HHV）无显著影响。若采用燕麦与大豆籽粒生产结合残余生物质能源化利用的模式，在维持免耕制度下70%秸秆还田覆盖率的前提下，年理论发电量可达2941吉瓦时（GWh）。