Nitrate and phosphorus loads

Daily nitrate-N, soluble reactive phosphorus and total phosphorus loads in subsurface drainage were quantified in an agricultural farm field in eastern Indiana (Davis Purdue Agricultural Center). Site description: The data was collected from the field W at Davis Purdue Agricultural Center (DPAC) located in eastern Indiana. Field W is relatively flat (slope Sampling strategy and load calculation: Automated water samplers (ISCO) were used to draw samples from the drainage outlet flow of each plot. Samples were collected every hour when flow was present except during winter, and combined into weekly composite samples varying in length from twice a week to biweekly. During the winter, water samples were collected manually to avoid freezing problems, approximately every week whenever flow was present. Samples were kept frozen until analysis and then analyzed on a SEAL Analytical AQ2 auto-analyzer to be tested for nitrate+nitrite-N (referred to nitrate-N), soluble reactive phosphorus (SRP) and total phosphorus (TP) according to US EPA methods. Daily nitrate-N, SRP and TP concentration values needed for the load calculations were estimated using linear interpolation. After estimating daily concentrations, daily loads were calculated by multiplying the daily drain flow by estimated daily concentrations. References: Saadat, S., Bowling, L., Frankenberger, J. and Kladivko, E., 2018. Nitrate and phosphorus transport through subsurface drains under free and controlled drainage. Water research, 142: 196-207.