Changes in phosphorus pools in the detritusphere induced by removal of P or switch of residues with low and high C/P ratio

The effect of the addition of crop residues to soil has been extensively studied; however, little is known about their effect on P pools in the detritusphere and how these pools change if the residue is replaced by another residue with similar or different P concentration. An experiment was conducted to determine the influence of a change of residue types on P pools in the detritusphere. Detritusphere soil was generated by placing 20 g kg(-1) of either mature barley straw (H; high C/P 255) or young faba bean residue (L; low C/P 38) between two fine nylon meshes which were then sandwiched between two PVC caps filled with loamy sand maintained at 50% water holding capacity throughout the experiment. Then, the open ends of the caps were pressed together and held in place with rubber bands. After 2 weeks of moist incubation, the residues were replaced with either a H or L, resulting in four residue treatments: high-high (HH), high-low (HL), low-low (LL), or low-high (LH) which were incubated another 14 days. A control without residues between the caps was unamended throughout. The following P pools were measured in soil at 0-1 mm from the surface 14 days after the first (day 14) and second (day 28) residue addition: readily available P (CaCl2 and anion exchange P); P bound to soil particles (citrate and HCl-P); and microbial biomass P (MBP). On day 14, P pools and available N were higher, but MBP and microbial biomass N (MBN) were lower in L than in H. On day 28, P pools and available N followed the order LL > HL > LH > HH, whereas MBN and MBP were highest in HL. In a second experiment, the effect of crop residue removal and replacement with anion exchange membrane (AEM) on P pools in the detritusphere was assessed. Detritusphere soil was generated using faba bean residue as described above. The control had no residues between the caps. After 2-week moist incubation, the residues and the meshes were removed and either replaced with three AEM strips (approximately 6 x 2 cm each) or left without AEM. The strips were replaced every 2 days for 2 weeks. P sorbed to the strips (AEM-P) was determined after removal. After 1 and 2 weeks, bioavailable P pools were measured. Removal of P by AEM decreased most P pools in faba bean detritusphere. This study showed that within 14 days, P pools in the detritusphere are influenced by P supply and P removal and that a change in the C/P ratio of added residue can either decrease or increase concentrations of various soil P pools.