Assessment of the nitrogen status of grassland

Abstract

Two types of diagnostics are used for N management in grasslands: diagnostics based on N concentration of shoots and diagnostics based on soil mineral N. The Nitrogen Nutrition Index (NNI) is an example of the first type. However, its evaluation requires the determination of shoot dry weight per unit area and, thus, constitutes a practical limit to its utilization in the context of farm studies. In order to simplify its evaluation, a method based on the N concentration of the upper sward layer (N up ) has been proposed. The objectives of this study were to test the relationship between NNI and N up in the context of permanent grassland and to examine the relationship between N up and soil mineral status. The study was conducted as two experiments, one on small cut-plots receiving contrasting rates of mineral N fertilization, and a second on plots of an existing field-scale lysimeter experiment. In each plot and at several dates, shoot biomass within quadrats was measured, N concentration was determined on the upper leaves and on the entire shoots, and mineral nitrogen of the soil below the vegetation sampled was determined. N concentration of the upper lamina layer of the canopy was linearly related to the NNI determined on the entire shoots. Therefore, determining N concentration in leaves at the top of canopy appears to be an alternative means to evaluate NNI without having to measure shoot biomass. The absence of an overall significant correlation between soil mineral N content and sward N index, observed over the two studies, indicates that each of these two indicators has to be considered specifically in relation to the objective of the diagnostic procedure. As sward N index may vary independently of soil mineral N content, the sward N indicator does not appear to be a suitable indicator for diagnosis of environmental risks related to nitrate leaching. However, soil mineral N content does not allow the prediction of sward N status and thus is not a suitable indicator of sward growth rate. Although soil mineral N content is an important environmental indicator for nitrate-leaching risks during potential drainage periods, it has a limited diagnosis value with respect to the herbage production function of grasslands.

Comparison of Five Nitrogen Dressing Methods to Optimize Rice Growth

“…Data collected before booting in experiment 1 to 4 were used to determine the threshold of LAI and SPAD at jointing and booting stages in the method of LAI (Wood et al, 2003) and SSNM (Peng et al, 1996). Data collected before booting in experiments 3 and 4 were used to construct the relationship between NNI and N dressing rate in NNI (Farruggia et al, 2004). Data in experiment 5 were used to calculate the dressing rate of fertilizer N in all five methods (Fig.…”

“…The N nutrition index (NNI) method was developed for the N dressing management (Farruggia et al, 2004;Lemaire et al, 2007Lemaire et al, , 2008Xue and Yang, 2008). NNI was estimated directly from canopy chlorophyll concentration predicted by canopy reflectance.…”

Potential of RapidEye and WorldView-2 Satellite Data for Improving Rice Nitrogen Status Monitoring at Different Growth Stages

“…It increases with increasing N rates. This trend remains constant during the growth period [45,46]. If N a is greater than N c (NNI > 1), it indicates a surplus of N while the opposite is true if N a is smaller than N c (NNI < 1).…”

Improved estimation of nitrogen uptake in grasslands using the nitrogen dilution curve

“…The N dilution curve can serve as a robust estimation of the N status of crops, including grasses, providing farmers and land managers an effective management tool (Farruggia et al 2004;Lemaire et al 2008). The N dilution curve depicts changes in plant N concentration during growth.…”