Characterization of phosphorus availability in selected New Zealand grassland soils

摘要: Appropriate evaluation of phosphorus (P) availability in soil is aprerequisite for ensuring the productivity and long-term sustainable managementof agroecosystems. Fifteen soils presently under grassland were collected fromdifferent areas New Zealand P was assessed by isotopicexchange kinetics (IEK) related to forms obtained chemicalfractionation (sequential extraction). Concentrations total determined inthe 15 ranged from 375 2607 mg kg−1(mean1104 kg−1). Mean concentrations inorganic P(Pi) extracted sequential extraction with ammonium chloride, sodiumbicarbonate, sodium hydroxide (first), hydrochloric acid hydroxide(second) 1.2, 41, 205, 113 23 kg−1,respectively. organic (Po) (first) (second) 133,417 105 kg−1, respectively. Similarly,results IEK analysis showed that intensity (water soluble Pi (Cp)),capacity (R/r1 n), quantity (E value,isotopically exchangeable pools (E1 min,E1 min–24 h,E24 h–3 m,E > 3 m)) factors varied markedlyamongst soils. Thus Cp 0.02–1.90 mgL−1, while theE1 min, E1 min–24,E24 m,E>3 m 2–29 (mean 10), 10–321(76), 11–745 (152), 8–498 (177) mgkg−1, The corresponding values forR/r1 n 1.0–17.7 4.5) and0.10–0.50 0.37), Regression revealed Cpconcentrations exponentially inversely proportional toR/r1,n sorption index (PSI)(R2 = 0.806(P < 0.01), 0.852 (P < 0.01) 0.660(P < 0.01), respectively). Cluster identified twobroad groups soils, namely those low Cp0.11 L−1, min 5mg R/r1 3.9,n 0.44), high 1.33mg 20mg 1.21,n 0.16). Correlation indicated thatE1 i significantly correlated bicarbonateextractable (BPi, R2 = 0.37,P < 0.05) thesum chloride extractable (APi) BPi(R2 = 0.38,P < 0.05). However, concentration pool generally lower than sum APi andBPi. Sodium (N1Pi) significantlycorrelated pools(R2 = 0.974, P < 0.01),indicating N1Pi fractioncould be considered as representing potentially available pasturespecies over a growing season.