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

Abstract

This analysis establishes linkage among (a) applied nutrients nitrogen (N), phosphorus (P), and potassium (K), (b) available soil nutrients, (c) root dry matter and nutrient content, (d) top dry matter and nutrient content, and (e) leaf area and carbon dioxide (CO 2 ) concentration. It was previously shown that (a) and (d) are coupled by logistic equations with a common response coefficient c between dry matter and plant nutrient uptake with each applied nutrient. As a consequence of the common c, it has been shown that dry matter and plant nutrient removal are coupled by a hyperbolic equation. Furthermore, a model has been developed which includes N, P, and K as inputs. In the present work, (a) and (b) were coupled by a logistic equation as were (a) and (c). It was then shown that plant nutrient removal was coupled to available soil nutrients through a hyperbolic equation. The hyperbolic relationship was also shown to link dry matter between roots and tops, as well as plant N removal between roots and tops. As a consequence of the results above, it was then concluded that root nutrient content is related to available soil nutrient through a hyperbolic equation. The detailed mechanism of this coupling was not identified. Leaf area of soybeans followed a hyperbolic relationship with CO 2 concentration in the canopy.

Model Analysis Of Forage Response To Split Applications Of Nitrogen. II. Coupling Of Roots And Tops*

“…Seasonal dry matter in the tops was related to plant N in the tops with a hyperbolic equation. Results in this article are consistent with those of previous analysis [2] of data from Blue [4] with Pensacola bahiagrass on Leon fine sand (sandy, siliceous, thermic Aeric Haplaquods) in Florida and from Wilkinson and Mays [5] with KY 31 tall fescue (Festuca arundinacea Schreb.) It was further shown that root dry matter and root N uptake could be related to these components in the tops by way of hyperbolic equations as well, which suggests that coupling of roots to tops can be treated as quasi-equilibrium Figure 4.…”

Nitrogen-Use Dynamics in Switchgrass Grown for Biomass

“…Nitrogen from such depths would likely not be from recent or current applications and would confound NUE estimations. Also confounding NUE calculations (where the implicit assumption might seem to be that N appearing in the biomass is a function of recently applied N) is the dynamic nature of the soil N pool, which can provide significant portion of switchgrass N demand [5].…”

An extended nitrogen, phosphorus, and potassium model for tall fescue

“…As shown in Figure 2, we estimated maximum potential yield of 23.8 Mg ha" 1 compared to estimated maximum yield from the field study of 12.0 Mg ha' 1 . Overman (1995) has speculated that one of the limitations on dry matter production by forage grasses might be CO2 concentration in the atmosphere. This point deserves further attention.…”

“…We now assume that, to first approximation, plant nutrient concentration for one element is essentially independent of applied levels of the other two elements. With this assumption, b p ' = b p and b^' = b^, so that plant N concentration, N c = N u /Y, can be written as: N c = N cm (1 + e b " " C " N )/(l + e b n' ' C " N ) [3] Similarly, for plant P concentration, P c , we assume that b n ' = b n and b^' = bj, so that: P c = P cm (1 + e b P " C P P )/(l + eV • C P P ) [4] and for plant K concentration, K c , we assume that b n ' = b n and b p ' = b p , and it follows that: [5] In Equations [3] through [5] maximum plant nutrient concentrations are given by: N cm = A n '/A, P cm = A-VA, and K cm = Aj.7A. These assumptions, which are to be justified with data, reduce the total number of possible parameters from twenty eight (four x seven) to thirteen.…”