Information

Nitrogen and water flows under pasture-wheat and lupin-wheat rotations in deep sands in Western Australia 2 – Drainage and nitrate leaching

Level 1 General description

Purpose:

To document the inputs of nitrogen, the temporal patterns of nitrogen mineralisation, the quantities of soil-derived nitrogen, and the extent of drainage and nitrate leaching by subterranean clover based pastures and grain lupin pastures in relation to climate and soil water.

Methods (brief)

Rates of N2 fixation by subterranean clover-based pastures and narrow-leaf lupin, plant uptake of soil-derived N, mineralusation of organic N during legume and cereal phases, and export of N from pastures, lupin and wheat were assessed through a rotation experiment.

Biomass production, grain yields, net N mineralisation, and N contents were standard plant measurements for all treatment, with soil water content, evapotranspiration (Ea), and inorganic N contents in soil were measured. N budgets were constructed for lupin-wheat and annual pasture-wheat rotations to determine the efficiency of utilisation of soil inorganic N by wheat, lupin and pasture.

Key findings (brief)

  • Pastures were large consumers of soil derived N (58 – 154 kg N/ha), while wheat and lupins were inefficient users of soil N (29 – 51 kg N/ha).
  • A high rate of decomposition of organic matter was observed due to the sandy soil (annual net N mineralisation ranged from 80 – 130 kg N).
  • Legumes were able to add adequate rates of organic N to soil to ensure rates of net N mineralisation sufficient to support cereal yields in excess of shire averages.
  • In practice, the asynchrony in supply and demand for N resulted in the inefficient use of soil-derived N by wheat.
  • The lupin-wheat treatment resulted in greater N/ha, 27kg (60% of total soil NO3) as opposed to the pasture-wheat rotation which resulted in 4kg N/ha (25% of total soil NO3).
  • The amount of NO3 in soil at the start of the growing season was affected by previous crop, with a lower range following wheat (31-68kg N/ha) than following legumes (40-106kg N/ha). The large quantities of NO3 in the soil at the break of the season contributed to NO3 leaching.
  • Greater N uptake by capeweed (Arctotheca calendula L.) than by either wheat or lupin was the main reason for the lower amount of NO3 leached in pastures.

Location

14km west of Moora, Western Australia

Related studies

N/A

 

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