Saturday, 15 July 2006

The Effect of Residue Characteristics on Phosphorus Availability and Plant Phosphorus Uptake.

Shahriar M. Iqbal, Else Bünemann, Petra Marschner, and Annie McNeill. The Univ of Adelaide, Soil and Land Systems, School of Earth and Environmental Sciences, DP 636, Adelaide, SA 5005, Adelaide, Australia

Crop residues can be a potential source for available phosphorus (P) to plants, but the influence of crop residue quality on the dynamics of available P and P uptake by plants is not well studied in Australian soils. The objectives of this study were to assess the relationships between residue characteristics (differing in nutrient contents, carbon quality and developmental stage) on soil P availability and plant P uptake. In this study, 10 crop residues from 6 crop species (canola, pea, lupin, lucerne, lentil and wheat) grouped into young (5), mature (4) and root (1) residues were added at 10 mg P kg-1 to a P deficient (Presin 1.3 mg P kg-1 soil) sandy loam soil incubated at 85% water holding capacity in the glass house at 10°C/18°C, 8 h night/16 h day for 84 days. Additional treatments included triple super phosphate (TSP) at 10 mg P kg-1 and an unamended control. The initial characteristics of crop residues were determined by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and wet chemical analysis. Wheat plants (Triticum aestivum cv. Yitpi) were grown for 4 weeks each during 3 consecutive growth periods. During incubation, soil samples were periodically analyzed for available P (Presin), microbial P (Pmic), biomass C (Cmic). Soil respiration, plant dry matter (DM) yield and P concentration in shoot and root were also determined. Presin concentration in soils decreased in the following order: TSP>root³young>control>mature, whereas Pmic concentration ranked in an approximately opposite order: mature>young³root>TSP³control. Presin in residue amended soil was correlated positively with total P and PH2O concentration in the residues and negatively with residue C: P, lignin: N, and phenolics: N ratios, whereas Pmic was correlated negatively with total P and PH2O concentration of residues and positively with the C: P, lignin: N, phenolics: N ratios of residues and Cmic. Generally, shoot and root DM yield of wheat ranked in the order TSP>root³young³control>mature during the 3 growth periods. Shoot and root P concentration in the plants was lower in plants grown in soil amended with mature residues than in all other treatments. Shoot and root P concentration were positively correlated with the P concentration in the crop residues. The results of this study show that young residues with low C: P ratio (132 - 252) have potential for increasing P availability and P uptake by plants. On the other hand, mature residues with high C: P ratio (504-874) lead to prolonged P immobilization, since even in the last growing period of the pot experiment (63-84 days after amendment), Presin and plant P uptake were still below values in the control treatment. Therefore, addition of crop residues can improve soil nutrient cycling while the value of their contribution depends on the chemical and biochemical properties of the residues.


Back to 3.3A Future Challenges in P Fertilization and the Environment - Poster
Back to WCSS

Back to The 18th World Congress of Soil Science (July 9-15, 2006)