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Fluid Journal : Fluid Journal 1996-1998
Fall 1996 occurs each year, the development of specific larval stages within the soil is relatively synchronized with the development of specific nodes of adventitious root axes. The fourth through sixth nodes of adventitious root axes sustain the most severe damage from corn rootworm larvae. Larvae tunnel within the cortex and stele of the root axis. If extensive feeding damage occurs, the entire root axis will die. Under conditions of light to moderate damage, with good soil fertility, many lateral "wound" roots will proliferate from the damaged root axis, leading to a foxtail appearance. Root pull resistance Greater root damage reduces root pull resistance and increases plant lodging. Linear regression analysis of data using root damage rating as the independent variable (Figure 2) reveals a close association between root damage caused by corn rootworm larval feeding and root pull resistance, as well as between root damage and plant lodging. Vertical root pull resistance (Figure 3) has been shown to be related to root size. The larger the root system the greater the force required to pull the root system from the ground. A close association between root pull resistance and lodging in rootworm damaged plants is present when root pull resistance is considered to be the inde- pendent variable (Figure 4). Increased root system size leads to reduced lodging and higher yields in rootworm damaged plants. These observations support the idea that a large root system is the basis of plant tolerance to rootworm larval feeding damage. N builds roots Research has shown that corn root systems respond to zones of increased N fertility. Root branching increases. Small, Figure 1. Plots of N, P, and K concentrations and levels from corn plants grown under irrigated no-till field conditions. Figure 2. Results of linear regression analysis of effect of root damage rating on root pull resistance (top), percent lodging (middle) and grain yield (bottom). 123456789 Root Damage Rating (1-9 scale) 79.5 76.3 73.1 70.0 66.8 60 40 20 0 RPR (lbs/plant) Lodging (%) Yield (bu/A) 308 264.6 220.5 176.4 132.3 Larval Feeding Activity 160 170 180 190 200 210 Day of Year 3 2 1 0 0.6 0.4 0.2 0.0 June 23 July 30 8000 6000 4000 2000 N or K Concentration (ppm) N or K Level (g/plant) 50000 40000 30000 20000 10000 P Level (g/plant) P Concentration (ppm) N K P
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