Effects of residues of 9 plants, lemon eucalyptus (Eucalyptus citriodora Hook., P1), robust eucalyptus (E. robusta Smith, P2), Nepal camphortree (Cinnamomum glanduliferum (Wall.) Nees, P3), tea (Camellia sinensis (Linn.) O. Ktze. f., P4), oleander (Nerium indicum Mill, P5), rape (Brassica campestris L., P6),Chinese tallow tree (Sapium sebiferum L., P7), tung (Vernicia fordii (Hemsl.), P8), and croton (Croton tiglium L., P9), 7 chemicals, boric acid (C1), borax (C2), oxalic acid (C3), sodium oxalite (C4), sodium dihydrogen phosphate (C6), sodium silicate (C7) and sodium citrate (C8), and a natural organic substance,humic acid (C5), on urease activity of a neutral purple soil and recovery of urea nitrogen by maize were studied through incubation and pot experiments. Hydroquinone (HQ) was applied as the reference inhibitor. After incubation at 37 ℃ for 24 h, 7 inhibitors with higher ability to inhibit urease activity were selected and then incubated for 14 days at 25 ℃. Results of the incubation experiments showed that soil urease activity was greatly inhibited by them, and the inhibition effect followed an order of P2＞P4＞C3＞C2＞P3＞C1＞HQ＞P1.The 7 selected materials reduced the accumulative amounts of N released from urea and the maximum urease activity by 11.7%～28.4% and 26.7%～39.7%, respectively, and postponed the N release peak by 2～4 days in the incubation period of 14 days under constant temperature, as compared to the control (no inhibitor).In the pot experiment with the 7 materials at two levels of addition, low (L) and high (H), the C1 (H), C3(H), C1 (L), P4 (L) and C2 (L) treatments could significantly increase the dry weights of the aboveground parts and the total biomass of the maize plants and the apparent recovery rate of urea-N was increased by 6.3%～32.4% as compared to the control (no hibitor).
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