Long-term effects of crop rotation, stubble management and tillage on soil phosphorus dynamics

Abstract

The effects of various management practices on soil phosphorus (P) dynamics were investigated in a field experiment in New South Wales, Australia, during 24 years of different crop rotation, stubble management, and tillage treatments. Topsoil samples collected at the beginning of the trial and after 6, 12, 18, and 24 years were analysed for resin-extractable P, inorganic and organic P, and total P. According to the calculated P input-output budget, 9-14 of the 20 kg P/ha added as superphosphate annually remained in the system, depending on the treatment. The measured increase in total P in 0-0.20 m did not differ between treatments, showing an accumulation rate of only 9 ± 2 kg P/ha.year. These results suggest a loss of 4 ± 2 kg P/ha.year, presumably into lower soil layers. Resin-extractable P at 0-0.10 m increased by 1.7 kg P/ha.year, irrespective of the treatment. The increase in total P after 24 years was almost completely accounted for by the increase in total extractable inorganic P. Changes in organic P paralleled changes in organic carbon, with a significant loss in treatments with stubble burning (wheat-lupin rotation and continuous wheat), and a significant accumulation in a wheat-subterranean clover rotation with stubble retention and direct drilling. We conclude that on the time scale of this experiment, the dynamics of carbon and organic P are closely linked.

Soil properties and not inputs control carbon : nitrogen : phosphorus ratios in cropped soils in the long term

“…The higher C and N budgets in the treatment WS-M-D were due to N 2 fixation, mulch retention and direct drilling, while the lowest budget reported for WW-B-C was due to regular cultivation, absence of significant N 2 fixation, and mulch burning. The P budgets were positive as reported by Bünemann et al (2006). The C and N budgets derived from Heenan et al (2004) were significantly correlated with each other (p < 0.05; Table S6) and both budgets were significantly correlated with the P budget calculated in this study (p < 0.05; Table S6).…”

Impact of reduced tillage on soil organic carbon and nutrient budgets under organic farming

“…Vu et al 58 found a concentration of plant-available P in 0-10 cm under NT. A high accumulation of C org was closely related to organic P dynamics, as organic P accumulates only when C availability is high 59 . Plantavailable K in the top layer was greater under RT, whereas there were no differences between RT and ploughed soil in 10-20 cm 5 .…”

Soil organic phosphorus and microbial community composition as affected by 26 years of different management strategies

“…Concentrations of resin-extractable P were high and not yield-limiting for annual crops (Cantarella et al 1998), which can be explained by 26 years of continuous P fertilisation. Thus, the higher annual wheat grain yield during the first 24 years of the trial in the wheat-lupin and wheat-subclover rotations (3.7-4.0 tons ha −1 ) compared to continuous wheat (2.2 tons ha −1 ) can be attributed, at least partly, to improved nitrogen supply in rotations including legumes (Bünemann et al 2006). The increase in total P in all treatments compared to 1979 confirmed the measured change in total P in the top 20 cm during the first 24 years of the trial (Bünemann et al 2006).…”

“…Findings from the trial have been published in a number of publications addressing wheat and lupin yields (Heenan et al 1994(Heenan et al , 2000 and various soil properties (Chan and Heenan 1993;Chan et al 2002;Heenan and Chan 1992;Heenan et al 2004;Heenan and Taylor 1995). Soil P dynamics during the first 24 years of the trial have been described by Bünemann et al (2006).…”

“…In a Luvisol in Australia, cereal-legume rotations in combination with stubble retention and direct drilling maintained or even increased soil organic carbon (C) over a period of 21 years, while tillage and stubble burning led to losses of soil organic matter, particularly under continuous cereal cropping (Heenan et al 2004). The grain yield of wheat was significantly lower in continuous wheat cropping than in rotations of wheat with lupin or subterranean clover (Bünemann et al 2006;Heenan et al 1994).…”