Nitrogen And Water Dynamics In Farming Systems

GRDC - Andrew Erbacher (Department of Agriculture and Fisheries, Queensland), Jayne Gentry (Department of Agriculture and Fisheries, Queensland), Lindsay Bell (CSIRO Agriculture and Food), David Lawrence (Department of Agriculture and Fisheries, Queensland), Jon Baird (New South Wales Department of Primary Industries), Mat Dunn (New South Wales Department of Primary Industries), Darren Aisthorpe (Department of Agriculture and Fisheries, Queensland) and Greg Brooke (New South Wales Department of Primary Industries)

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

The authors of this paper note in the conclusion: “Improved pulse varieties and agronomy has seen greater use of pulses. This has not provided increased nitrogen benefits to following crops as the pulse crops often mine mineral nitrogen from the profile. However, increasing nitrogen budgets to 90th percentile yield potential at planting has meant crops have left nitrogen behind in most seasons, so the nitrogen can move down the profile and accumulate in the deeper soil layer”.   Please access the full paper via the link below if this research interests you.

The take home messages from this GRDC funded research are below. Please access the full paper via the link below for methodology, references, acknowledgements and discussion.

Take home messages from the paper include:

  • Grain legumes have utilised soil mineral nitrogen (N) to the same extent as cereal crops and have higher N export which often offsets N fixation inputs
  • Additional applied N reduced the depletion of background soil mineral N status at most sites; we are recovering a high percentage (>50%) in soil mineral pool.
  • Application of ~50 t/ha of compost or manure (10 t/ha OC) coupled with N fertiliser rates for 90th percentile yield potential has dramatically increased the soil mineral N in four years
  • Decreasing cropping frequency has reduced N export and so stored more N over the longer fallows, which has reduced N fertiliser requirements for following crops
  • Long fallows are mineralising N and moving N down the soil profile even under some very dry conditions
  • Most excess N is not lost in the system rather it is moved down the soil profile for future crops
  • The marginal WUE of crops (i.e. the grain yield increase per extra mm of available water) is lower when crops have less than 100 mm prior to planting. Hence, waiting until soil moisture reaches these levels is critical to maximise conversion of accumulated soil moisture into grain
  • The previous crop influences the efficiency of fallow water accumulation with winter cereals > sorghum > pulses. Long fallows are also less efficient than shorter fallows (<8 months). This has implications for assuming how much soil moisture may have accumulated during fallows.

2020 - Australia - GRDC - Andrew Erbacher (Department of Agriculture and Fisheries, Queensland), Jayne Gentry (Department of Agriculture and Fisheries, Queensland), Lindsay Bell (CSIRO Agriculture and Food), David Lawrence (Department of Agriculture and Fisheries, Queensland), Jon Baird (New South Wales Department of Primary Industries), Mat Dunn (New South Wales Department of Primary Industries), Darren Aisthorpe (Department of Agriculture and Fisheries, Queensland) and Greg Brooke (New South Wales Department of Primary Industries)
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