More Profit from Nitrogen: Optimising Nitrogen and Water Interactions in Cotton
Abstract
Organic matter in soil can supply more than 50% of the nitrogen (N) to cotton crops, but this pool of N supply is dynamic and difficult to predict. Soil bacteria are responsible for mineralising soil organic N and hydrolysing dissolved urea to ammonium. Most plants can take up both ammonium and nitrate forms. However, nitrate is susceptible to leaching and can be denitrified into inert and greenhouse gases. Filterable organic N (dissolved organic nitrogen, DON) is the most readily available form for microbial mineralisation and can also leach. The type and timing of N fertiliser and irrigation may regulate N supply and loss, as the severity of soil drying between irrigation events regulates microbial activity. The ‘Optimising nitrogen and water interactions in cotton’ project investigated how ammonium, nitrate and organic N in soil is affected by urea and DMPP-treated urea fertilisers during wetting and drying cycles of irrigated cotton. DMPP urea is an enhanced efficiency fertiliser that slows the conversion of ammonium to nitrate in soils.
The main objectives of this research were to: (1) investigate how N fertiliser formulations; namely: urea and DMPP-treated urea, and wet/dry cycles affect within- season patterns of soil N supply, (2) identify how well a rapid soil test based on water extraction and measurement of dissolved organic N or potassium chloride-extractable inorganic N species can inform predictions of soil mineralisable N, and (3) suggest how currently available nutrient management DSSs can be improved by improved knowledge of within-season patterns of soil N supply.
The research was conducted in soils established to overhead irrigated cotton on commercial farms over the 2016/17 and 2017/18 seasons in the Darling Downs of south-east Queensland. Soil was sampled after key irrigation or rainfall events, and at critical cotton growth stages. Soil was sampled from outside and inside root exclusion tubes that were placed in the soil to a depth of 300 mm at the beginning of each season,
to monitor the plant-available pools of soil and fertiliser N in the presence and absence of roots, respectively. Novel, low-cost, rapid methods were used to measure nitrate, ammonium and total dissolved N (mineral N and DON). The results were compared with conventional N testing methods for their ability to predict crop N availability.
Files in this item
This item appears in the following categories
- 2018 Final Reports
CRDC Final Reports submitted 2018