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Fluid Journal : Fluid Journal 2002-2004
Monitoring nutrient status Color patterns. Fortunately several key nutrient deficiencies are associated with distinct color patterns within a leaf. Detection of nutrient deficiency symptoms within a crop provides an early warning of pending problems and an opportunity to use tissue testing to verify the cause and magnitude of a stress. In some cases, other plant colors and pigments may mask deficiency symptoms. For example, nearly every nutrient deficiency affects leaf chlorophyll content, which is typically expressed as greenness. Yet, some nutrient stresses, such as P, also affect other parts of the photosynthetic process. Insufficient plant P results in the accumulation of sugars in leaves (i.e., reduced phosphorylation to build structural components) which prompts the synthesis of anthocyanin (reddish- purple color). This purplish color on the margins of corn leaves also can be induced by cold or wet soils and various kinds of plant damage. Biomass/photosynthesis. Two major plant processes are worthy of further discussion when it comes to N management. Collectively, these two processes are sometimes discussed in terms of plant vigor. Sometimes it is convenient to think of plant biomass as it relates to size of the factory (i.e. exterior view), and photosynthesis as to how fast the factory is working (i.e., interior view). The SPAD chlorophyll meter is essentially a potential photosynthesis meter because it measures how much radiation can be used under excess light conditions. The device, however, is not able to assess leaf area index (LAI) or biomass. When observing corn plants for biomass, we must scan the object for spatial details Figure 1. Cumulative dry matter production and total N uptake for irrigated corn. Average yield of 178 bu/A across six hybrids and three replications. Figure 2. Dry matter production and N uptake rates for irrigated corn in Nebraska. 0 2000 4000 6000 8000 10000 12000 14000 16000 130 150 170 190 210 230 250 270 290 Calendar Date (Days) Dry Matter (lbs/A) 0 20 40 60 80 100 120 140 160 N Uptake (lbs/A) Accumlated DM Total Uptake 0 50 100 150 200 250 300 350 400 450 500 130 150 170 190 210 230 250 270 290 Calendar Date (Days) Dry Matter (lbs/A/day) 0 1 2 3 4 5 N Uptake (lbs/A/day) DM Growth Rate N Uptake Rate and interpret these details according to established criteria. Essentially, human vision and our reasoning ability are roughly equivalent to what should be possible with remote sensing and a closely coupled decision aid. Canopy reflectance. History has provided considerable information about the relationships between plant canopy reflectance and biophysical processes such as photosynthesis and plant biomass production. It has been well documented that near-infrared Early Spring 2003
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