Corn crops

P. Rochette and L. B. Flanagan, Quantifying rhizosphere respiration in a corn crop under field conditions. Soil Sci. Soc. Am. J. 6/ 466 (1997). 

Nitrogen. Total N used by a corn crop is relatively small during the first six to seven weeks (3 ) but increases rapidly thereafter as the corn plant approaches tasseling (Figure 5). Applied N, and that present in soil, may be in many different forms. Some forms are readily soluble and others are not. Sooner or later the organic and insoluble forms undergo nitrification to soluble inorganic forms in soil. Water-soluble N, unlike P and K, is freely mobile in soil. Thus, the depletion zone of N can extend well beyond the plant s roots in soil. 

Hageman, R.H., Flesher, D. Gitter, A. (1961). Diurnal variation and other light effects influencing the activity of nitrate reductase and nitrogen metabolism in corn. Crop Science 1, 201-4. 

Fig. 3. Kinghead Ambrosia growing within corn crop.

A "fuel or food" debate is also in progress, because biofuels are made from agricultural products and therefore they drive up food prices. Today 33 nations are at risk of social unrest because of the rise in food prices (most of their families spend 75%-80% of their income on food). In the United States, a fifth of the corn crop is used to brew ethanol and as more com is planted shortages develop in other produce, such as soybeans. 

The U.S. bioethanol industry is growing rapidly. Production in 2007 was 6.5 billion gallons from 139 bioethanol refineries. A further 4 billion gallons of capacity are expected to come online by the end of 2008. In 2006,14% of the corn crop in the United States was used to produce ethanol and probably as a result, com prices increased by 25% in 2007. In the United States 90 plants operated in 2006 and 160 in 2007. Just in Iowa, 42 ethanol and biodiesel plants are in operation and an additional 18 are under construction. A study by the Organization for Economic Cooperation and Development calculated that in order to meet 10% of the fuel requirements of the United States, Canada, and the EU, 30% to 70% of their crop area would have to be devoted to biofuels. 

Caro, J.H. Glotfelty, D.E. Freeman, H.P. (Z)-9-Tetradecen-l-ol formate Distribution and dissipation in the air within a corn crop after emission from a con-trolled-release formulation. Presented at the American Chemical Society/Chemical Society of Japan Chemical Congress (PEST 081), Honolulu, April 1-6, 1979. 

The availability of these residues depends on regional agricultural productions and on the commitment of agricultural cooperatives in favour of agromaterials. For instance, in France, at present, there are corn crops dedicated exclusively to the fabrication of thermoplastic agromaterials. 

To illustrate the relative contributions of various air layers from the ground to the top of a corn crop 2 m in height (Fig. 9-4), we will let Kj have specific average values for various height intervals above the ground (Table 9-1), consistent with the plot of Kj versus height in Figure 9-4. We can use Equation 9.4 (r , = Az/Km, = r ) to estimate the resistance of each of the four air layers in series. For example, for the lowermost layer we obtain... 

In a sense, we are performing a numerical integration to determine the resistance.) Computer analyses using models describing the turbulent air within such a crop also indicate that the resistance is usually 300 to 400 s m-1. Most of the resistance within a plant community is generally due to the relatively still air next to the ground. For instance, just over half (200 s m-1 out of 350 s m-1) of the resistance for the 2-m pathway is provided by the lowest 0.01 m, whereas the entire upper half of the corn crop accounts for a resistance of only 10 s m-1 (Table 9-1). 

CO2 concentrations in the air can vary over a wide range within different plant communities. For a corn crop exposed to a low wind speed (below 0.3 m s-1 at the top of the canopy), for a rapidly growing plant community, or for other dense vegetation where the eddy diffusion coefficient may be relatively small, the CO2 mole fraction in the turbulent air within the plant stand can be 200 pmol mol-1 during a sunny day. On the other hand, for sparse desert vegetation, especially on windy or overcast days, generally does not decrease even 2 pmol mol-1 from the value at the top of the canopy. 

Figure 9-8. C02 resistances, flux densities,and concentrations within and above a corn crop at night. Height in the turbulent air above the plant canopy is not to scale. Air temperature is 20°C, and the atmospheric air pressure is 0.1 MPa (see Table 8-2 for the conversion factor between mmol m-3 and (xmol mol-1).

Any factors that stimulate the growth of soil microorganisms or that increase the availability of pesticides in soil will enhance the degradation of the chemical. Felsot et al. (1981) found that the persistence of carbofuran was inversely correlated with microbial activity in corn-cropped soils. Tu and Miles (1976) reported that 88% of parathion was lost from soil in 7 months diazinon, 92% lost in 20 weeks paraoxon, 100% hydrolyzed in 12 hr mala-thion, 50-90% lost in 24 hr and carbofuran, 50% lost in 3-50 weeks. 

Look tor the big eyes Bigeyed bugs are your triends, unlike chinch bugs, which munch on the roots ot your lawn or corn crop. 

Wright, J.L., and Lemon E.R. (1966) Photosynthesis under field conditions, VIII. Analysis of wind speed fluctuation data to evaluate turbulent exchange within a corn crop, Agron. J. 58, 255-261. 

Ladisch MR, Gong C-S, Tsao GT (1977) Corn crop residues as a potential source of single cell protein kinetics of Trichoderma viride cellobiase action. Developments in Industrial Microbiology 18 157-168... 

An herbicide, atrazine, which is commonly used on corn crops in the mid-western United States, was chosen as an example. During the spring, rainfall washes this compound from soil, and concentrations of herbicide in surface water will reach the Environmental Protection Agency s annual maximum contaminant level of 3 gg/L. It is necessary to detect this compound at concentrations as low as 0.05 gg/L. How would one isolate and purify this compound from water for analysis by gas chromatography/mass spectrometry (GC/MS) using SPE Some questions and ideas that come to mind follow ... 

These cultural and chemical practices have prevented, moderated, or eliminated enhanced biodegradation in soils, and preserved the effectiveness of EPTC, EPTC + dietholate, and butylate herbicides in corn cropping systems. 

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