Combined effects of partial root drying and patchy fertilizer placement on nutrient acquisition and growth of oilseed rape

Partial rootzone drying (PRD) is widely investigated as an effective irrigation technique, resulting in higher water use efficiency and yield for plants growing under mild water deficit. Nutrition is another important factor affecting plant yield, but nutrient acquisition has only rarely been considered in conjunction with PRD. Here we investigate the interaction between water and fertilizer supply in a pot experiment with oilseed rape (Brassica napus L.). Eight treatments were set up for the experiment, a factorial combination of four watering regimes (100% control watering at both sides of the plants; 50% control watering at both sides of the plants; 50% fixed watering applied only to one side of the plants; 50% alternate watering applied alternately to both sides of the plant) and two fertilizer placement levels (uniform over the entire pot, and patchy supplied to one side). For the 50% watering treatments, the total amount of water supplied to the plants was the same, only the pattern of application differed between treatments. Also the total fertilizer applied was the same for all treatments. Oilseed rape roots foraged effectively for water and nutrients resulting in relatively small differences in nutrient uptake and above-ground growth among the water-deficit treatments. Placing fertilizer at one side of the plants increased nutrient uptake, but there were differences between the water treatments and interactions with water uptake. Alternate watering resulted in the highest growth, as a result of the largest nitrogen and phosphorus uptake with the smallest root investment among the three water deficit treatments. Fixed watering resulted in poorest performance when fertilizer was uniformly spread throughout the pot, because the plants were unable to acquire the nutrients on the dry side. Our results show that PRD can be well combined with patchy fertilizer supply, but that reduced nutrient uptake may be expected when nutrients are supplied in parts of the soil volume that remain too dry.