Phosphorus dynamics under burnt crop residues

Transcription

1 Phosphorus dynamics under burnt crop residues Joginder Gill School of Earth and Environment Supervisors: W/Prof. Zed Rengel Dr. Bill Bowden Funding: International Postgraduate Research Scholarship, Australian Postgraduate Award, UWA Completion Scholarship & Underwood PhD Top-up Scholarship

2 Crop Residues Total crop residue production 3.8 billion tons/ year 74% cereal crops 10% sugar crops 8% legumes

3 Importance of crop residues Maintain the productivity of soil Improve the physical properties of soil Increase the biological activity in soil Better soil health and plant growth

4 Management of crop residues Retained Removed Incorporated into soil Left on the surface Burnt Household fuel Feed and bedding material for animals Building material Biofuel production

5 Reasons behind burning of crop residues timeliness of field operations better control of weeds and diseases absence of alternative uses lack of appropriate machinery

6 Consequences of burning Loss of nutrients through volatilisation Almost complete loss of Nitrogen 5 to 60% loss of Sulphur Around 20% loss of Potassium and Phosphorus Irreversible transformation of nutrients

7 Phosphorus Critical macronutrient Significant amount in soils But < 1% plant available

8 Different forms of phosphorus in soil Inorganic P Solution P Residue Pi Microbial biomass Residue Po Organic P Crop residue Plants

9 P fractions and Plant availability Soil or Crop residue P Anion exchange resin or water only 0.5 M NaHCO 3 (ph 8.5) 0.1 M NaOH 1 M HCl Concentrated acid digestion Resin or water Pi NaHCO 3 -Pi NaHCO 3 -Po NaOH- Pi NaOH- Po HCl- Pi HCl- Po Residual P Readily available P Moderate availability Very low availability

10 Research Questions: Burning and effects on total phosphorus in residues and the distribution of P fractions? Effects of addition of burnt residues on growth and P uptake by wheat

11 Methodology Four different type of residues: Wheat straw, pea straw, oat hay and lucerne Burnt at a range of temperatures: Unburnt, C, C, C and C Burnt residues were analysed for: Total elements, water-soluble elements, Colwell P and distribution of different P fractions

12 Total P (g kg -1 residue) 20 UB Unburnt 200 C 300 C 400 C 550 C d c 15 d c c b c b b a b a a a a a a a a a Wheat WSstraw Lucerne L Oat OH hay Pea PS straw

13 Water-soluble P (g kg -1 residue) 4 UB Unburnt 200 C 300 C 400 C 550 C d 3 e c b e d c a a e b d d c c b a b a a WS L OH PS Wheat straw Lucerne Oat hay Pea straw

14 Water-soluble P as percentage of total P Wheat straw Oat hay Lucerne Pea straw Temperature of burning of residue ( 0 C)

15 Distribution of P fractions Residual P NaOH-P Water-P HCl-P NaHCO3-P UB 200 C 300 C 400 C 550 C Temperature of burning of wheat straw UB 200 C 300 C 400 C 550 C Temperature of burning of oat hay

16 Distribution of P fractions UB 200 C 300 C 400 C 550 C Temperature of burning of lucerne forage 0 UB 200 C 300 C 400 C 550 C Temperature of burning of pea straw

17 To summarise the results: Burning of residues increased total P Water-soluble P decreased with temperature of burning Burning changed the distribution of P in residues Most of P was detected in HCl fraction Low availability

18 Growth and P uptake by wheat Phosphorus applied: 2 and 20 mg kg -1 soil Sources of Phosphorus: Inorganic fertiliser, four residues burnt at C and C Wheat: grown for 6 weeks shoots and roots- dry weight and P concentration

19 Shoot dry weight (g pot -1 ) Control 20P UB Unburnt 300 C 550 C Control 20P Wheat WS straw LLucerne OH Oat hay Pea PSstraw

20 Root dry weight (g pot -1 ) 2.9 Control 20P UB 300 C 550 C Unburnt Control 20P Wheat WS straw Lucerne L OH Oat hay Pea PS straw

21 Total P uptake (mg pot -1 ) Control 20P UB Unburnt 300 C 550 C Control 20P Wheat WS straw LucerneL OH Oat hay Pea PS straw

22 Conclusions Burnt residues significantly increased wheat growth and P content compared to the unburnt residues. Wheat growth and P content was the largest in legume crop residues burnt at C and cereal crop residues burnt at C. Wheat growth was higher in the inorganic fertiliser treatment than burnt residues, but P uptake was comparable in both the treatments