Theoretical Determination of a Critical Nitrogen Dilution Curve Based on the Carrot Case Study
The objectives of the present study were to: (a) formulate a general dilution equation for a critical nitrogen percentage in a leaf (Nc); (b) monitor dilution function of carrot as a case study; (c) demonstrate applicability of digital color imaging to monitor total nitrogen (Ntot) in crops. Carrot (Daucus carota) was grown on loess soil at five Ntot application rates. Ntot weight (kg/ha) was obtained by standard laboratory analysis and by image processing. Total yield of the treatments was the sum of canopy and roots dry matter. A new logistic decay curve Nc = a/[1 + (W/W0)b] agreed with experimental data. Nc (g/kg) is the critical nitrogen level, a and b are coefficients, and W/W0 is the relative dry matter biomass. Values of Nitrogen Nutrition Index (NNI) ≥ 1.0 indicated that there was no nitrogen deficiency in treatment larger than 100% application of Ntot. The weight of nitrogen in form of multiplication of the dry leaves weight (W) and N percent is suitable for the determination of nitrogen status. The availability of image-based data for N percent is faster, timely and less expensive than that of laboratory test. Applicability of digital color camera to monitor Ntot in crops instead of laboratory test was successfully demonstrated.
Determination of a Critical Nitrogen Dilution Curve for Winter Oilseed Rape
Abstract Several controlled environmental and field experiments were carried out to define the critical nitrogen dilution curve for winter oilseed rape, cultivar Goeland. This curve is described by the following power equation:N=4.48 W-0.25,whereNis the total nitrogen concentration in the shoot biomass andWthe shoot biomass. This curve has been validated over the range of shoot dry matter of 0.88 to 6.3 t ha-1. For lower shoot biomasses this equation overestimated the critical nitrogen concentration; we propose a constant value of 4.63 (Nis expressed in reduced N, which is a more stable N fraction in the shoot at these stages of development). These results have been validated in several pedoclimatic conditions in France on a single variety in 1994 and 1995. The higher position of this curve relative to the C3species reference curve (Greenwoodet al.,Annals of Botany67: 181–190, 1990) can be explained by the experimental conditions obtained by Greenwoodet al. (1990); therefore, all their rape data are rather close to the critical curve that we propose. The differences found between wheat and winter oilseed rape critical N dilution curves correspond to their respective leaf:stem dry matter ratio and the specific leaf loss phenomenon occuring in rape. Winter oilseed rape has a higher capacity of N accumulation in its shoot than wheat for the same aerial dry matter. The proportion of nitrate in shoots rises with the nitrogen nutrition index (N.N.I.) and is more important for rapeseed than for wheat for the same N.N.I. This difference is especially high at the beginning of flowering when the shade provided by the canopy of rapeseed flowers decreases nitrate reductase activity.
Effect of Soybean Cyst Nematode (Heterodera glycines) on Yield of Resistant and Susceptible Soybean Cultivars Grown in Ohio.
Soybean (Glycine max) producers in Ohio rarely use soybean cyst nematode (Heterodera glycines, SCN)-resistant cultivars because of concerns over limited yield potential and lack of resistance to Phytophthora sojae. A two-year study was initiated to determine grain yield and nematode population increase on soybean cyst nematode-resistant cultivars in maturity groups II and III in production fields. Sites differed in soil texture, nematode densities, and P. sojae infestation at a number of locations in Ohio. Soil was assayed for nematode densities before planting and at harvest. Yields of resistant cultivars averaged 0% to 18% higher than those of susceptible cultivars in fine-textured soils with average preplant populations ranging from 463 to 14,330 SCN eggs/100 cm(3) soil. In coarse-textured soils, yields of susceptible cultivars were 21% to 56% less than the resistant cultivars with average preplant densities ranging from 1,661 to 15,558 SCN eggs/100 cm(3) soil. The reproductive index ranged from 0.1 to 5.5 for resistant cultivars and 0.4 to 112 for susceptible cultivars. In 1993, yield of P. sojae-susceptible, nematode-resistant 'Asgrow A 3431' was as high as yield of the P. sojae-resistant, nematode-susceptible cultivar 'Resnik' in a Phytophthora-infested field. The nematode-resistant cultivars Madison Experimental 131527 and Asgrow A3431 had higher yields than AgVenture AV1341 and susceptible cultivars Resnik and Kenwood when compared over five nematode-infested sites. Nematode-resistant cultivars were found to be excellent alternatives to currently grown susceptible cultivars for managing SCN where group III cultivars are used. However, better cultivar alternatives may be needed for sites with combined Phytophthora root rot and cyst nematode problems.