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Tightening nutrient cycles in the crop-soil-water ecosystem

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Researchers at the James Hutton Institute are working on a number of ways to tighten nutrient cycles.

This involves a combination of knowledge into how to reuse societies 'wastes' such as sewage effluent discharges as valuable nutrient resources, ways to make crop-soil systems smarter to maintain yields with declining inputs of chemical fertilisers, and how to minimise losses of nutrients from fields to waters via measures such as multifunctional buffer strips.

One aspect of this work is being explored by a soil phosphorus research group involving James Hutton Institute scientists with other UK and international colleagues. Our position paper on this work Recovering Phosphorus from Soil: A Root Solution? was published in the journal Environmental Science and Technology 46, 1977–1978.

Model

Figure 1: Nutrient cycle

A conceptual model of the sizes, roles and accessibility of different soil phosphorus pools in relation to crop availability is shown above (figure 1).

Sizes of boxes and arrows depict the relative magnitudes of pools and pathways in P cycling. The average European fertiliser excess rate exceeding crop uptake is 12 kg P ha-1 year-1 and this excess P accumulates as stabilised inorganic orthophosphate and monoester P according to the following processes (numbered arrows).

  • 1. Stabilisation against leaching and crop uptake via geochemical sorption.
  • 2. Immobilisation of crop residue P and microbial conversion to monoesters followed by sorption.
  • 3. Rapid P turnover within microbial P pools competing with crop uptake.

We suggest that compensating for future declines in fertiliser P inputs without losing yields can be achieved by combining methods to increase agronomic P use efficiencies (in relation to letters).

  • A. Better targeting (spatially and temporally) fertiliser inputs.
  • B. Utilising crop biotechnologies to improve P access via (i) P desorption by organic acid excretion, (ii) enzyme release of refractory monoester P, and (iii) increasing root architecture.
  • C. Manipulation of soil microbes to stimulate P turnover (e.g. manipulating soil wetting and drying cycles that enhance P mineralisation rates).
  • D. Reducing losses of leached and eroded P in runoff coupled with retention and recycling methods to reincorporate P back into fields (from diffuse pollution, food, animal and human waste streams).

Not one of these methods alone will be likely to succeed and a combined strategy is required.

Research

Areas of Interest


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The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.