An Extended Model of Forage Grass Response to Applied Nitrogen

Abstract

A simple model is needed that relates forage grass production (yield and N removal) to management factors (applied N, harvest interval, and water availability). The objective of this analysis was to extend a previous model to include quantitative coupling between yield and N removal in response to applied N for perennial grasses. The extended model was developed from three postulates: (1) annual dry matter yield follows logistic response to applied N, (2) annual plant N removal follows logistic response to applied N, and (3) the N response coefficients are the same for both. Three additional consequences derive from these postulates: (i) plant N concentration response to applied N follows a ratio of logistic functions, (ii) annual dry matter yield and plant N removal are related by a hyperbolic equation, and (iii) plant N concentration and plant N removal follow a linear relationship. Data from a field study in Louisiana with dallisgrass [Paspalum dilatation Poir.] grown on Olivier silt loam (fine‐silty, mixed, thermic Aquic Fragiudalf) were used to demonstrate applicability of the model and to illustrate procedures. Analysis of variance supported Postulate 3 for these data, with an overall correlation coefficient of 0.9990. Plant N concentration (Nc for this study was bounded by 11.8 <Nc< 27.5 g kg−1. Maximum yield for the study reached 57% of potential yield at plant N removal of 427 kg ha−1. Potential yield of 27.5 Mg ha−1 appears to be in the range of values reported in the literature. Further use of this model should provide added insight into the coupling among various mechanisms that control forage production.

Within-season grass herbage crude-protein- and nitrate-N concentrations as affected by rates and seasonal distribution of fertilizer nitrogen in a high yearly rainfall climate

“…Others have examined the potential of plant N concentration as a measure of whether or not grass growth is limited by available N (Overman et al 1994(Overman et al , 1995Salette et al 1983). Belanger and Richards (1997) proposed using the ratio of plant N to an independently derived optimum N concentration to differentiate deficient (ratio < 1) from sufficient to luxuriant plants (ratio > 1).…”

Coupling among applied, soil, root, and top components for forage crop production

“…Recently, Overman et al (1994) extended the model to include logistic response of plant N removal to applied N through the equation: Nu = A7(l + eb'-'N) [2] where: Nu = plant N removal, kg/ha, A 1 = maximum plant N removal, kg/ha, and b 1 = intercept parameter for plant N removal. Overman et al (1994) showed that accumulation of dry matter and plant N is coupled through a common c parameter for Equations [1] and [2] (unpublished) has demonstrated that this extended model applies to each of the three major nutrients (N, P, and K) and that it also applies to cool season forage grass.…”

“…Overman et al (1994) showed that accumulation of dry matter and plant N is coupled through a common c parameter for Equations [1] and [2] (unpublished) has demonstrated that this extended model applies to each of the three major nutrients (N, P, and K) and that it also applies to cool season forage grass. Plant N concentration is defined as the ratio, Nc = Nu/Y, and is described by:…”

“…Overman et al (1994) further showed that a consequence of Equations [1] and [2] is that yield and plant nutrient removal are related by a hyperbolic equation:…”

Simulation of rice biomass accumulation by an extended logistic model including influence of meteorological factors

“…If the influence of temperature is incorporated into the model, the model will not only describe characteristics of population growth, but also express the limiting effect of the environment. For example, Overman et al (1994), Overman (1995), Overman and Wilkinson (1995) extended the logistic model by taking account of the dependence of the increment in biomass upon the length of time before harvest and water availability (year-to-year). In the extended model, the parameters were taken to be functions of nutrient and water content.…”