Nitrogen crop yields

Mixed fertilizers contain two or more of the elements nitrogen, phosphorus, and potassium (NPK), which are essential for good plant growth and high crop yields. This subsection briefly addresses the production of ammonium phosphates... 

Therefore, as suggested by the vertical lines beginning at week 6, competition for N may occur earlier than for P and K but somewhat later than for water. Thus, competition for N may account for a significant part of the total crop yield reduction from weeds but likely accounts for little of the earliest observed crop yield reduction in nonlegumlnous crops. For the purpose of this discussion, it is assumed competition for nitrogen does not occur with leguminous crops. 

Figure 5. Crop Response to Weed Presence, left, and Relative Nitrogen Uptake by Corn, right. Closeness of the vertical lines indicates the relative possibility of competition for N being a factor in crop yield reduction.

On the basis of results to date, it is concluded, as shown in Figure 7, that allelopathy could be a source of crop yield reduction throughout the time crop yields are reduced by weed presence, but it is most apt to be a factor from the midpoint of the curve on. Thus, the contribution of allelopathy to crop yield reduction likely is less than that of competition for light, water, and nitrogen. The reduction in crop yield could be the result of inhibition in growth, inhibition in reproduction, or some combination of the two. 

Kahnt, G. and Hijazi, L. A. 1991. Use of lupinex to increase crop yield and improve harvest quality with lesser nitrogen fertilization. Journal of Agronomy and Crop Science, 166 228-237. 

In a 250-mL, round-bottomed flask equipped with magnetic stir bar, 1-bromoadamantane (35.0 g, 0.16 moles) is dissolved in 3,5-dimethylanilinef (92.0 g, 0.75 moles), yielding a clear, pale yellow solution. This is heated under nitrogen for 24-36 h at 140°C to form a thick brown liquid. The reaction is conveniently monitored by GC/MS. The brown liquid is extracted with ether (200 mL), washed with NaOH (100 mL of a 1 M solution), and vacuum distilled to remove excess aniline, leaving a dark brown solid. The solid is extracted into a minimum volume of hot methanol (ca. 160 mL) and cooled until crystallization occurs. The solid is collected on a sintered-glass frit and washed with cold methanol (2 x 20 mL) to afford white crystals. The filtrate is concentrated again to afford second and third crops. Yield 29.0 g (71%). 

Between 1956 and 1972, world crop yields grew in tandem with increases in the use of nitrogen fertilizers. 

Figure 13.11 Ammonia is essential in the production of fertilizers containing nitrogen. Proper levels of soil nitrogen lead to increased crop yields. 

Soil pH is one of the most important factors that affect the availability of Mo to plants. There are interactions between Mo and a number of nutrients, such as sulfur, nitrogen, phosphorus, and copper, that can affect its plant availability. Although large concentrations of Mo show no effects on crop yields of grains and forage crops, feeds containing Mo in excess of 10mgkg- when fed to ruminants, can produce severe Mo toxicity (Mo-induced copper deficiency). 

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