CROP rotation and fertiliser research in Canada that began in 1925 (92 years ago), and continuing to this day, shows interesting (one might say predictable) and valuable long-term crop performance and soil quality trends.
Correction of soil deficiencies has resulted in far higher crop performance.
Soil organic matter is higher where deficiencies are corrected. Rotations involving a two-year lucerne phase after three cereal crops further dramatically improves yield even with good fertiliser use for both continuous cereals (cereal followed by fallow) and the rotation.
Ignoring elements once considered high in a given soil, in this case potassium, will also eventually run out if not addressed via fertiliser.
Not surprisingly wheat yield in the wheat-fallow-wheat rotation without fertiliser resulted in yield of 0.2 tonnes a hectare in 2016, indicating exhaustion of important elements like nitrogen, phosphorus and sulphur. In contrast wheat in the same rotation with fertiliser (nitrogen, phosphorus, sulphur) yielded 1t/ha.
Wheat yield without fertiliser in the wheat-oats-barley hay-hay (lucerne) rotation yielded 2.2t/ha. Clearly a response to nitrogen and other rotation benefits.
The top yield was from the same rotation, but where fertiliser was used. Wheat yield was 3.4t/ha. Note this part of Canada is relatively low rainfall having an average annual total of around 360 millimetres.
Soil organic matter in the wheat-oats-barley-hay-hay rotation with no fertiliser was 3.1 per cent (0 to 15 centimetres depth) compared to 4.5pc in the fertilised treatment with nitrogen, phosphorus, sulphur, plus potassium.
Fertilised treatment with no phosphorus was 3.8pc.
Dick Puurveen, author of the study’s report, published in the Better Crops 2017 number 1 edition, noted that the long-term research “continues to teach the importance of nutrient management and crop rotation”.
Potassium responses were negligible, indicating the initial high level of it in the research site.
However, soil testing has noted a steady decline with levels now approaching critical values.
In nil fertiliser and fertiliser treatment that exclude phosphorus, soil tests indicate very low levels; 6 and 7, compared to greater than 60 for the phosphorus fertilised treatments. Likewise, sulphur soil readings were very low for no sulphur plots compared to sulphur treated plots of 3, verses up to 36.
Critically, lack of fertiliser resulted in poor root development, with plants severely stunted and spindly. There was a lack of tillering and plants were yellow. However, stunting was less in the non-fertilised wheat grown in the rotation that included lucerne.
Plots supplied with fertiliser, but missing either sulphur, nitrogen or phosphorus, also saw strong deficiency symptoms. Sulphur deficiency especially results in poor root development, poor tillering and necrosis of older leaves.
Nitrogen deficiency (far less in the rotation treatments because of legume nitrogen input) is typified by yellowing and lack of overall growth.
Phosphorus deficiency also shows up as poor root development, stunted plants and poor tillering. Lack of root development leads to inability of plants to access moisture and other nutrients.
Long term research studies like this one are important for many aspects other than to define the need to monitor soil fertility and to supply missing elements like phosphorus.
Long term cropping is also shown to be more than sustainable (for example higher organic matter) when combined with appropriate rotations with adequate nutrient replacement.
Next week: Acid soils crops and pastures. Highlight of 35 years of Down to Earth
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
