Dynamics of plant-soil interactions in grassland community succession with companion species


T. Paul*

Low-fertility soils and frequent droughts are typical characteristics of rainfed wheat production methods, which create an unfavourable environment for long-term crop growth. In this work, the water balance and nitrogen (N) dynamics in soils under rainfed wheat agriculture at low (219 mm, Pygery) and medium (392 mm, Yeelanna) rainfall sites in south Australia were assessed over the course of two seasons using a processed-based biophysical numerical model. The model was calibrated, validated, and the water and nitrogen consumption efficiency of wheat were calculated using estimated evapotranspiration components and data on N partitioning. The predicted water balance components for the two sites differed significantly from one another. At the low rainfall site, more than 40% to 50% of the rainfall was absorbed by plants. On the other hand, leaching losses at the medium rainfall site (Yeelanna) of up to 25% of seasonal precipitation show a large volume of water eluding the root zone. Ammonia-nitrogen (NH4-N) contributed little to plant nutrition, according to the model-predicted N partitioning, and its content in the soil stayed below 2 ppm for the majority of the crop season, with the exception of the period right after NH4-N-based fertiliser application. The majority of N uptake during both seasons at both locations was facilitated by nitrate-nitrogen (NO3-N). The primary causes of the N losses from the soil at the medium rainfall location (3.5-20.5 kg ha-1) were NO3-N leaching (NL) and NH4-N volatilization (Nv) below the crop root zone. Climate, water availability, and N dynamics in the soil all contributed to the extreme variability in water productivity (8-40 kg ha-1 mm-1) and N usage efficiency (31-41 kg kg-1). These findings imply that managing N applications to maximise wheat output and reduce N losses in rainfed agriculture can be accomplished by combining water balance and N modelling.

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