Florida Lawn Nitrate Leaching, continued from page 1
Figure 1. In-ground lysimeters collected run-off from each plot for sampling.
center of each experimental plot at a depth of 4” below ground. The lysimeters were 22” in diame- ter and 42” tall (Figure 1). They were placed into metal bulkhead units and polyethylene tubing was fitted to the base of each unit. Tubing ran from underground to above ground collection boxes. A vacuum was applied to the tubing to evacuate the lysimeters on a twice weekly or weekly basis. A 25 ml subsample of the Leachate was taken and sent to the
Analytical Research Lab on campus for analysis of nitrate-N. Data from all projects are expressed in units of kg ha-1, which is a measurement of the nitrate-N loading that occurred based on nitrate-N concentration and volume of leachate.
Nitrate-N leaching due to N rate and irrigation from newly planted turfgrass
‘Empire’ zoysiagrass and ‘Floratam’ St. Augustinegrass
were sodded and N treatments were applied the same day at rates of 0.5, 1.0, 1.5, or 2.0 lbs N 1,000 ft-2. Nitrogen was applied as water soluble urea. Half of the plots received the same treatments 30 days later. Nitrate-N leaching from both grasses over all years was considerably greater than from the established grass studies, regardless of N rate. The percent of applied N that leached from St. Augustinegrass was 73.4% of what was applied the same day as planting in 2006 (Table 1). Leaching from the plots that received a second treatment 30 days later was reduced to 56.4% of the applied N. Similar results were seen in the other years.
Table 1. Percent of applied N leached as nitrate-N when applied to newly planted St. Augustinegrass at day of planting and 30 days after planting.
2006 Day of Planting 30 Days After Planting 2007
% of applied N leached 73.4 56.4
Newly planted turf, whether sodded, seeded, sprigged, or
plugged, should not be fertilized with N for at least 30 and up to 60 days after planting due to the potential for large nutrient losses before a root and/or shoot system has been estab- lished. This is now a Best Management Practices (BMP) recommendation.
There were few statistical differences in nitrate-N leached due to N rate in St. Augustinegrass (Figure 2). Where there were differences (primarily Fall 2007), greatest nitrate-N load occurred at the highest N rate. During this study, the St. Augustinegrass was in good health and had good growth and cover. The dense root and shoot system provided the grass the ability to take up nitrogen at the excessively high rates applied to some of the plots (7 and 10 lbs 1,000 ft-2 yr-1, which far exceeds the current recommendations for fertilizing St. Augustinegrass in north central Florida). Nitrate leached did not exceed 1.4% of the applied N in any fertilizer cycle and was generally below 1% of that applied N. Increased leaching occurred in the fall of 2007 at the 10 lb N rate in response to increased disease and associated injury due to the high rates of N. This reduced the cover and density of the grass, with the resulting higher leaching quantities. Zoysiagrass had a statistically greater tendency to leach more nitrate-N as N rate increased. This was especially true in the Spring and Early Summer Fertilizer Cycles in 2007 (Figure 3). Many of the zoysiagrass cultivars in use today need less N to keep a green, healthy cover and excess N will promote greater thatch production and generate more disease problems. The higher rates of N applied in this research are an example of the effects of overfertilization with N on this grass.
Nitrate-N leaching due to N rate and irrigation from established turfgrass
Nitrogen was applied to Empire zoysiagrass and Floratam
St. Augustinegrass over a 3-year study. Annual N rates were 1, 4, 7, or 10 lbs N 1,000 ft-2 applied every 60 days throughout the growing season. Nitrogen was applied as water soluble urea through a backpack sprayer. Leaching data are presented for 2006 and 2007 for each of the four Fertilizer Cycles (the 60-day interval between each fertilizer application). Fertilizer cycles are presented as Spring (April-May), Early Summer (June-July), Late Summer (Aug-Sept), and Fall (Oct-Nov).
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