Effects of soil compaction and moisture regime on the root and shoot growth and phosphorus uptake of barley plants growing on soils with varying phosphorus status

The effects of soil compaction state and level of water supply on plant growth and phosphorus (P) uptake were studied in a pot experiment with spring barley (Hordeum vulgare L.). Three soils (loamy, clay loam and silt texture) were used, each with three levels of plant available P in soil (low, medium and high P-AL). The soils were compacted to two levels, 75 and 90% of the standard degree of compactness attained with free drainage under a load of 200 kPa, and they were maintained at two levels of water supply (20 and 30% mass wetness). Total root length (RL) was 59% lower at the higher of the two compactness levels, mainly due to fewer roots with diameter < 0.5 mm. However, both shoot growth and plant P uptake were reduced a lesser degree then RL. This means that 69% more shoot dry-matter (DM) per unit RL was produced in the compacted soil, and that the P uptake per unit RL was 75% higher in the more compacted soil. Thus, the plants must have compensated for reduced RL by increasing their uptake of water and nutrients per unit RL, although this did not fully compensate for the reduced RL. The effects of moisture regime on shoot growth varied between the different soils. On the clay loam soil, there was a significant yield increase with high water supply at alt three soil P-AL levels. The same was true on the loam soil at medium and high soil P-AL levels. On the silt soil, the high level of water supply increased yield by 62%, but only at the highest soil P-AL level. The plants grown on the silt soil at low and medium levels of plant available P showed marked symptoms of P deficiency throughout the growth period.