Abstract
With the increasing unpopularity of uncontrolled straw and stubble burning, two field experiments were carried out to investigate the effects of burning stubble using the Calor Gas flame cultivator.Winter barley was sown in the 1986/87 and 1987/88 seasons using a range of seed bed preparation techniques at three nitrogen levels in a sandy loam to sandy clay loam soil in a 2 x 3 x 3 factorial experiment. Trials looked at stubble removal, crop growth and development, soil physical and chemical properties and soil and fertilizer nitrogen uptake using 15N labelling techniques.
The flame cultivator significantly reduced height and weight of stubble. It significantly increased grain yields in 1987/88 but just failed to do so in 1986/87. Stubble burning had no effect on ploughed ground but increased yields from minimal cultivation and direct drilling by up to one tonne per hectare. Grain yields were similar to those on ploughed ground where stubble was burned prior to minimal cultivation and direct drilling in 1986/87 and minimal cultivation in 1987/88. Yield increases were attributed to a significantly greater plant stand in 1986/87 and significantly more ears per square metre in both experimental years. Straw yields were not affected by stubble burning.
Soil pH, phosphorous, potassium and magnesium and weed and disease levels within the crop were unaffected by stubble burning. Inorganic nitrogen within the cultivation layer of the soil and plant nitrogen uptake were not significantly influenced by stubble burning but inorganic nitrogen levels tended to be lower in direct drilled ground than ploughed or minimally cultivated. While stubble burning significantly reduced soil organic matter, it tended to increase the total nitrogen within the crop and soil where seed was direct drilled. It appeared to increase the uptake of nitrogen from the soil and reduce fertilizer nitrogen uptake by the minimally cultivated and direct drilled crop.
Stubble burning in these trials was believed to reduce nitrogen immobilization in the presence of decomposing stubble. This was important where soil was direct drilled and mineralization was lower than in ploughed or minimally cultivated soil, due to the lack of soil disturbance. Poor grain yields from the minimally cultivated crop in the presence of stubble were attributed chiefly to toxic organic acid production from the decomposing residues which were mixed into the surface soil by minimal cultivations, bringing them into close contact with sown seed.
The flame cultivator used was a prototype and was still subject to modification before it could be promoted commercially. The removal of stubble before minimal cultivation and direct drilling was considered essential for obtaining adequate grain yields but economics of using the flame cultivator would need to be considered. However, if uncontrolled straw and stubble burning are banned, use of such a machine may remain the only viable alternative if minimal cultivation and direct drilling are to be used.
| Date of Award | Dec 1989 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | D.L. Easson (Supervisor) |