不同土地利用方式下紫色土中铵的容量和强度(Q/I)关系

摘要

研究了4种土地利用方式下(水田、旱地、林地、菜地)紫色土(紫色湿润雏形土)和紫色水稻土(紫色水耕人为土)NH4+的容量和强度( Q/I)关系.结果表明:紫色土和紫色水稻土NH4+ Q/I曲线的曲线部分均出现在NH4+的活度比( ARNH4)较低时,表明土壤存在非交换性NH4+(或专性吸附的NH4+)的释放.紫色土和紫色水稻土NH4+的潜在缓冲容量(PBC)为71.47～203.7 cmol kg -( mol L -1)-1/2；土壤活性NH4+(-ΔNH04)为0.029 5～0.089 7 cmol kg-1,NH4+的平衡活度比(AR0NH4)为0.187 × 10-3～ 1.255×10-3(mol L-1)1/2;土壤专性吸附位点(NH4-sas)为0.0106～0.118 5 cmol kg-1.相关分析和通径分析表明,土壤小于0.002 mm黏粒含量与NH4+ PBC及NH4-sas均呈极显著正相关(p＜0.01),小于0.002 mm黏粒对PBC的影响主要是间接作用(间接通径系数为0.585),但对NH4-sas则有强烈的直接作用；有机碳与- ΔNH04和ARONH4均呈极显著正相关(p＜0.01),但是有机碳对-ΔNH04有较大的直接效应(直接通径系数为0.966),而对ARONH4的影响主要以间接效应为主.土壤- ΔNH04与交换性NH4+数值接近且呈极显著相关(γ=0.876 4,n=8,p＜0.01),而AR0NH4与交换性NH4+亦呈极显著相关(r=0.983 7,n=8,P＜0.01).土壤小于0.002 mm黏粒和有机碳的差异是导致不同土地利用方式下紫色土交换性NH4+以及Q/I参数的差异的主要原因,交换性NH4+标志的NH4+有效性指标与由Q/I关系得到的NH4+有效性指标类似.%Quantity-intensity (Q/I) relationships of NH/ in purple soils and purple paddy soils different in land use (paddy field, dry land, woodland and vegetable plot) were studied. It was found that in both 0 -20 cm and 20 -40 cm layers of the two soils the curve of NH+4 Q/I relationships were observed only when NH+4 activity ratios in the soils were low, suggesting release of nonexchangeable (or specifically adsorbed) NH+4 in the soils NH+4 in the two soils ranged from 71. 47 to 203. 7 cmol kg-1 (mol L-1) -1/2 in potential buffering capacity (PBC) , from 0. 029 5 to 0. 089 7 cmolc kg-1 inlabile NH4 (- △NH°4) , from 0. 187 × 10-3 to 1. 255 × 10 -3 (mol L-1) 1/2 in equilibrium activity ratio (AR°NH4) and from 0. 010 6 ～0. 118 5 cmol kg-1 in specific adsorption sites (NH4-sss). Correlation analysis and path analysis indicate that the content of clay (<0. 002 mm) is in extremely significant positive relationship with both PBC and NH4-sss(p <0. 01). The effect of clay (< 0. 002 mm) is mainly indirect on PBC (indirect path coefficient, 0. 585) , but strong and direct on NH4-sss, Positive linear relationships were observed of organic C with - ANH°4 and AR°NH4 in all soil samples. The effect of organic C is high and direct on - △NH°4(direct path coefficient, 0. 966) , but indirect on - △NH°4. The concentration of exchangeable NH+4 is positively related to - △NH°4(r = 0. 876 4, n = 8, p < 0. 01) and they are approximate in value. Moreover, exchangeable NH+4 is also positively related to AR°NH4(r =0. 983 7, n=8,p<0. 01). This study clearly demonstrates that differences between the soils in clay and organic C are the main reason for the differences in exchangeable NH+4 and Q/I parameters between purple soils different in land use. The use of exchangeable NH+4 as indicator of NH+4 availability has a similar effect as the use of Q/I relationships.