Phosphorus availability under continuous point source irrigation

Phosphorous fertigation applied in a microirrigation system provides increased P use efficiency relative to traditional banding. This project investigated the hypothesis that continuous, low-intensity irrigation can provide plants with available P more efficiently than intermittent drip fertigation. Objectives of the study were to characterize water and P distribution when provided to soil by a continuous point source, and to raise P fertilizer efficiency by increasing plant available P without augmenting P application rates through maintenance of relatively constant conditions within the root zone. Plant response, soil P distribution, and soil moisture were compared for an intermittent irrigation regime, giving water for 4 h once every 2 d, to continuous application of the same amount of water in both a water-solute simulation model (Hydrus-2d) and in greenhouse-lysimeter experiments with and without a corn crop on a calcareous sandy loam soil. Results from both the simulation and the lysimeter-soil study showed that the hypothesized zones of increased available P materialized when P-laden water was applied continuously at low application rates to an un-cropped soil. Extractable P concentrations in the soil immediately surrounding the point source were found to be 20 to 25% higher in continuously irrigated soil as compared with pulsed irrigation. After 40 d of growth, corn plants grown under continuous fertigation yielded 20% greater biomass than plants irrigated with the same water quantity and quality once every 2 d. Phosphorus content of corn leaves was 25% greater for the continuous treatment as compared with the pulsed treatment.