Understanding plant growth and development under subsurface drip fertigation (SDF)

Intensive agriculture has transformed the farming production in many regions to a great extent due to increased use of fertilizer to supply with nutrients essential to the growth of plants. Nutrient element losses and declining soil fertility have increased the necessity of searching for efficient ways of managing natural resources to obtain high water and nutrient use efficiencies. Furthermore nitrate pollution of groundwater from agriculture is an issue of major concern in many regions. The main reason for the high loss of nitrogen is the asynchrony between nutrient availability and crop demand, i.e. mineral nitrogen is applied during the time when there is still no plant uptake, but sufficient rain to cause leaching, particularly after heavy rainfall events in light soils and during the winter. Moreover, water and nutrients limitations will be more frequent in the coming decades due to climate change along with regulations aiming at protecting water resources. These issues lead to the need of innovations in agricultural production to improve water and nutrient use efficiencies.
Subsurface drip fertigation (SDF) is the fertigation, i.e. irrigation combined with application of fertilizer dissolved in the water, of crops through plastic tubes permanently buried below soil surface. These tubes or driplines include built-in emitters to drip water to the surrounding soil. This allows placing the water and fertilizers directly into the crop root-zone. Burying driplines underground minimizes surface soil evaporation and avoids runoff due to irrigation. Furthermore SDF system has a great potential to minimize or eliminate the movement of water and nutrients below the root-zone when effectively managed. Through the combined application of nutrients and water, drought and nutrient stresses can be diminished and yield potentials optimized. SDF systems can therefore make cropping systems not only more environmentally friendly and sustainable, but also more resilient to climatic fluctuation. Moreover these systems enable higher yielding reducing the land area necessary for agricultural production along with production risks.
Understanding and modelling the behaviour of plants under SDF has some open questions. One of these questions is the root distribution and growth dynamics of plants under this irrigation system. Research and experiments need to be set-up to determine the influence of SDF on root growth and its spatial distribution. The spatial root distribution in the soil profile affects the water/nutrient uptake by the roots. Furthermore little research has focused on actual evapotranspiration as the traditional estimation of evaporation and transpiration may not accurately describe them when SDF is used as the primary irrigation source. Transpiration is the process of water evaporation from the aerial part of plants and is regulated by the stomata. Monitoring the transpiration of plants irrigated by the SDF system will contribute with understanding this process. Moreover further research related with the influence of SDF on plant growth dynamics and root-shoot partitioning is required.
The aim of this project is to address these open questions based on experimental set ups and development of models. The overall concept of research is divided into 4 different modules that are interconnected. These modules are: soil transport, root growth dynamics, root uptake and plant growth. Both water and nutrients are included within each of these modules and models will be established to explain the different components under SDF.