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Deep ploughing improves nutrient distribution and crop performance

P.N. Vance

Queensland Department of Primary Industries, PO Box 23, Kingaroy, Qld 4610

There has been widespread adoption of reduced tillage in the South Burnett District of Queensland. Improvements in surface tilth, water infiltration and erosion control have been observed. Reduced tillage has enabled more intensive cropping resulting in an overall increase in productivity rather than an improvement in individual crop yield.

Some paddocks are now showing uneven growth, development and yield of maize and navy beans under reduced tillage with potassium and phosphorus deficiency symptoms visible in poor areas.

Preliminary tests have shown that levels of phosphorus and potassium in surface soil are adequate but are deficient in the subsoil. Deep ploughing improved soil test values in the subsoil and this was associated with improved growth and grain yield of navy beans in 1987/88 (Table 1).

Table 1. The effect of tillage and soil tests on navy bean yields

These observations have implications regarding soil test sampling and interpretation, tillage management and fertilizer placement. A need for more intensive soil sampling under minimum tillage has been suggested (1) and while (2) indicates that no-till crops can meet their P and K requirements from starter fertilizer.

Trials in 1988/89 comparing (a) deep ploughing (inverted to 250 mm), (b) deep ripping to 450 mm without inversion and (c) reduced tillage using chise1 ploughing to 150 mm are showing more uniform and even growth of peanuts and soybeans in treatment (a). Soils are being analysed for both physical and chemical attributes for each 50 mm interval down the profile.

1. Anon (1988). Banding of fertilizers and minimum-till are creating soil sampling problems. The Australian Conservation Farmer, Vol. 1. No. 1, 16.

2. ICI Americas Inc. (1988). No Till Farming. Wilmington, Delaware, USA.

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