Measuring and modeling nitrate-nitrogen movement in soils following manure injection.

摘要

Injection spacing and lateral movement of manure nutrients in the soil following manure injection are important characteristics to determine proper liquid manure placement in soil. A three-year manure injection field experiment was conducted in Manitoba, Canada in the growing seasons of 2002, 2003, and 2004 on clay soils. Liquid swine manure was injected into soils in spring using coulter and furrower injectors at 0.3-, 0.6-, and 0.9-m tool spacings which correspond to three manure application rates: 1.02, 2.04, and 3.06 litters per meter of manure band. Effects of the two manure injection tool types and three tool spacings on the overall soil nutrient levels and crop response and soil nutrient distribution and crop response at different lateral positions relative to injected manure bands were investigated. Measured soil variables include: extractable soil NO3-N, NH4-N, P2O 5, K, SO4-S, pH, and electrical conductivity (EC). Soil variables were measured on soil samples collected at 0, 0.15, 0.30, and 0.45 m lateral distances from the centre lines of manure bands. Measured plant variables include number of tillers, heads, and main stem length, plant biomass, grain and straw yields, total N and P in plant biomass, grain, and straw.;Injection of manure with furrower proved to be advantageous over coulter in many ways. Use of furrower resulted in 40 to 60% higher soil NO3-N than coulter at 0-0.3 m soil depth at the time of rapid plant development in the second and third years of the experiment. Furthermore use of furrower resulted in 10% more plant biomass, 13, 3, and 16% higher total N in plant biomass, grain, and straw, 2.5 and 13% higher total P in grain and straw, respectively, compared to the use of coulter in the first year of the experiment. Among tool spacings, the 0.3 m tool spacing resulted in the best plant performance and the most elevated nutrients in plant parts as compared to the 0.6 and 0.9 m spacings.;The soil NO3-N, NH4-N, and P2O 5 concentrations and soil EC were significantly lower at a farther position from the centerlines of manure bands, especially at the highest manure application rate. Plants in the crop row further from a manure band had 25% fewer tillers, 20% fewer seed heads, 10% shorter stem length, 60% less plant biomass, and 25% lower total N in the plant biomass, compared to those in the crop row close to the band.;A soil sampling protocol that enables accounting for banding effects of manure injection was developed based on soil nutrients data from the field study. A directed paired-sampling approach (sampling at two positions along a transect perpendicular to the injector travel direction) was suggested to obtain more accurate estimates of average soil NO3-N and P concentrations than the traditional random sampling method.;A model for simulating NO3-N movement in cropped soils following manure injection was developed. The domain for modeling NO3-N movement was a cross sectional area defined by two hypothetical lines, each mid way between centerlines of two consecutive manure bands in the vertical plane. Hydrus-2D software package was used to calibrate and validate the model. The model was validated using a separate set of data collected from field experiments (different from those used to calibrate the model). The model predicted soil NO3-N concentrations satisfactorily over the growing season and laterally at 0.0, 0.15, 0.30, and 0.45 m distances from center line of manure band. Model predictions at the abovementioned lateral distances from manure band revealed that manure nitrate nitrogen does not move laterally beyond 0.15 m from the manure band. The model predictions were consistent with the experimental data.;Keywords. Manure, injection, tool, tool spacing, soil, nutrient, crop, yield, position, sampling protocol, modeling, nitrate movement.