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Daily vs. Periodic Nitrogen Addition Affects Growth and Tissue Nitrogen in Perennial Ryegrass Turf

Dep. of Crop Sci., North Carolina State Univ., Raleigh, NC 27695

View larger version (28K): [in a new window]   Fig. 1. Growth rate of perennial ryegrass turf with daily N additions (top) or intermittent N additions (bottom). Note the different ranges of the x-axes. Arrows indicate intermittent N additions, with long, intermediate, and short arrows representing the 32-d, 16-d, and 8-d additions, respectively. Values are means of three replicates. For clarity, error bars are absent; standard deviation averaged 7%.

View larger version (13K): [in a new window]   Fig. 2. Weekly values for integrated photosynthetic photon flux density (PPFD) in the greenhouse during the experiment.

View larger version (22K): [in a new window]   Fig. 3. Growth rate of perennial ryegrass treated with daily N as a function of photosynthetic photon flux density (PPFD). Values are means of three replicates. Slope values followed by the same letter are not significantly different at P = 0.05.

View larger version (30K): [in a new window]   Fig. 4. Concentration of reduced N in the clippings from perennial ryegrass turf grown with daily N additions (A) or intermittent N additions (B). Arrows indicate intermittent N additions, with long, intermediate, and short arrows representing the 32-d, 16-d, and 8-d additions, respectively. Values are means of three replicates. For clarity, error bars are absent; standard deviation averaged 3%.

View larger version (21K): [in a new window]   Fig. 5. Growth rate of perennial ryegrass grown with daily N additions (A) or intermittent N additions (B) as a function of reduced N concentration in the clippings. Values are means of three replicates.

View larger version (33K): [in a new window]   Fig. 6. Concentration of NO3–N in the clippings from perennial ryegrass turf grown with daily N additions (A) or intermittent N additions (B). Symbols and arrows as in Fig. 1. Values are means of three replicates. For clarity, error bars are absent; standard deviation averaged 16%.

View larger version (17K): [in a new window]   Fig. 7. The relationship between NO3–N and reduced N in the clippings of perennial ryegrass turf grown with daily N additions. Data are compiled from all five daily N additions and are the means of three replicates.

View larger version (22K): [in a new window]   Fig. 8. Nitrate uptake by perennial ryegrass turf grown with daily N additions (A) or intermittent N additions (B). Data from Treatment 5 (highest daily N) included in (B) for comparison. Values are means of three replicates; error bars are standard deviations.

View larger version (24K): [in a new window]   Fig. 9. Cumulative N harvested in clippings of perennial ryegrass turf grown with daily N additions. The percentage of absorbed N allocated to new leaf growth was calculated as the ratio of the slope of each curve to the daily N addition rate. Values are means of three replicates.