Effects of compaction during drilling on yield of sugar beet (Beta vulgaris L.)

Excessive soil compaction can reduce crop growth, but compaction can also have positive effects, e.g. increasing soil unsaturated hydraulic conductivity and thereby the capillary flow of water and nutrients to seeds and plants. There may thus be an optimum state of compactness for plant growth.This study examined the effect of different levels of compaction on sugar beet growth and sugar yield in a total of 10 field experiments performed during 2006–2008, mainly on sandy loams (Eutric Cambisols). In most cases, the soil had been mouldboard-ploughed in autumn. A newly constructed sugar beet seed drill with press wheels was used to create different levels of compaction directly around the seed. Greater compaction was achieved by 1 or 3 passes by tractor wheels over the soil. The actual degree of soil compaction was determined by measuring bulk density at 5–10 cm depth and penetration resistance to 30 or 35 cm depth. Crop growth was determined by measuring root and plant biomass in mid-June and final sugar beet yield. The concentration of plant nutrients in sugar beet foliage was also determined. Two additional experiments in 2009 examined different levels of traffic in combination with mouldboard ploughing or chisel ploughing to 10 or 20 cm depth.On average, one pass with a tractor wheel increased yield compared with uncompacted soil, but increasing the compaction by press wheels on the seed drill had little effect on yield. In most cases, even three passes with tractor wheels had no harmful effect on sugar yield. The effect of traffic on nutrient concentrations in the plant was also very small. In one experiment, shallow tillage with a chisel plough lowered yield compared with mouldboard ploughing. There was also an interaction between the effects of primary tillage and compaction in the spring, with more negative effects after shallow tillage.Overall, the sugar beet crop was relatively insensitive to different levels of traffic applied at the time of sowing. The results indicate that the risk of yield losses due to compaction caused by normal traffic after autumn ploughing is low. However with ploughless tillage, soil bulk density may be too high for optimal growth regardless of traffic during seedbed preparation.

► The sugar beet crop was relatively insensitive to different compaction levels.
► Even three passes with a tractor did on average not decrease yield compared with no traffic.
► Moderate recompaction by tractor traffic had a positive effect on sugar beet yield.
► With ploughless tillage, bulk density may be too high for optimal growth.