Chemistry of throughfall, stemflow and litterfall in fertilized and irrigated Pinus radiata

The chemical inputs by rainfall, throughfall and stemflow were studied in a pine plantation located in Pierces Creek Forest, Canberra, Australia. Three treatments were included in the study: a control (C) and two fertilizer treatments. The first fertilizer treatment (F) involved two applications of mixed fertilizers at high rates, the second (IL) involved application of a complete liquid fertilizer with irrigation, so as to remove nutrient and water restrictions to growth. The application rates of nutrients were higher for IL than F. Net inputs of elements in throughfall and stemflow, obtained by subtracting the amounts in the rainfall, were compared for different treatments. For cations (the sum of Ca, Mg, Na and K), the treatment effect on leaching by throughfall and stemflow was IL > F > C; but the F to C differences were greater for throughfall than stemflow. The effects were almost entirely due to increases in concentration, rather than the amount of rainfall becoming throughfall or stemflow. The concentration of nitrogen (as NH4 or NO3) in throughfall or stemflow could be lower or higher than in rainfall, indicating net removal or leaching, respectively. Net removal occurred for most rainfall events for the control treatment, for a substantial number of events for treatment F, but for few events for treatment IL. The ammonium ion was preferentially removed from throughfall, and nitrate from stemflow. Transfers of potassium and total nitrogen by litterfall, throughfall and stemflow were also studied. The proportions of potassium and nitrogen being transferred by these processes showed little difference between treatments; the overall values for potassium being 60% by throughfall, 4% by stemflow and 36% by litterfall. In contrast the transfer of nitrogen was dominated by litterfall (81%), with 18% by throughfall and 1% by stemflow. (C) 1997 John Wiley & Sons, Ltd.