Effects of Water Table Management and Liquid and Solid Manures on Phosphorus Losses in Surface and Sub-Surface Drainage Water and Crop Performance.

Understanding phosphorus (P) loss in soils receiving nutrients from various sources in combination with drainage water management strategies is important to develop risk assessment tools and BMPs that minimize adverse impacts of agricultural practice on water quality. An experiment was conducted in a clay loam soil of Eastern Canada over a 4-year period to determine crop yields and soil P losses in surface runoff (SR) and tile drainage (TD) as influenced by additions of liquid (LCM) and solid cattle manures (SCM), in comparison with chemical fertilizer (CF), under regular free drainage (RFD) and controlled drainage/sub-irrigation (CDS). Cropping system was corn-soybean rotation, with a unified amount of P, 50 kg P ha-1, added from each of the three sources to the corn phase. Surface runoff and TD flows were monitored and samples collected continuously year round using an auto-sampling system. Water samples were analysed for dissolved reactive (DRP), dissolved un-reactive P, and particular P. Both P source and drainage water management affected corn yields, but not on the soybean yield. Corn yield was the highest with CF, followed by SCM, with the LCM the lowest. Controlled drainage and sub-irrigation decreased slightly the corn yield, relative to RFD. Annual total P losses (ATPL) through both SR and TD were 4740 g P ha-1 in the CF control plots, but decreased to 4383 and 3834 g P ha-1 with added LCM and SCM, respectively, under RFD. Under CDS, ATPL was 4228 g P ha-1 in the CF control plots, and decreased to 3996 and 3453 g P ha-1 with added LCM and SCM, respectively. Of the ATPL, from 40% to 63 % was attributed to P loss in sub-surface tile drainage water. Dissolved reactive P accounted for 26, 23, and 50% of the soil P loss for CF, LCM and SCM treatments, respectively, and the percentages were similar between RFD and CDS. Annual total soil P loss followed the order of CF>LCM>SCM, but generally reduced with CDS, regardless of P sources. An optimized combination of nutrient source with drainage water management must be developed to maximize production profitability, while minimizing soil P losses to water resource.