Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO₃)₂; +N and –N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined.Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO₃ ^– and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H⁺ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO₃ ^– but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO₃ ^–, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO₃ ^– is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO₃ ^– had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner     

The time-into-intensity-mapping network

We employ a special combination of different networks in order to process (transient) spatiotemporal patterns. In a first layer, feature analyzing cells translate instantaneous spatial patterns into activities of cells symbolizing the presence of certain feature values. A second layer maps the time sequence of symbols into a spatial activity pattern of the so-called TIM-cells. A third layer recognizes predefined activity patterns. We demonstrate the behaviour of the network using gaussian patterns in (1 + 1) space-time dimensions.     

Effects of the chemical form of inorganic nitrogen fertilizers on the dynamics of the soil solution composition and on nutrient uptake by wheat

Adding nitrogen (N) fertilizers to soil affects not only the concentration in the soil solution of the added ions, but also those of other ions already present in the soil. This secondary effect is caused by ion exchange and electrochemical equilibrium processes. We studied how different N fertilizers affected the chemical composition of the soil solution over time, and how this related to nutrient uptake by wheat. Soil was fertilized either with (NH4)2SO4 or Ca(NO3)2, or no N was added. Each of these N treatments was either planted or not with spring wheat (Triticum aestivum L.). Soil solutions were collected repeatedly with looped hollow fiber samplers from the root zone in situ, six times during a 50-day pot experiment. Plants were harvested five times, and their nutrient contents determined. In the soil solution, NO3- was significantly less concentrated if (NH4)2SO4, rather than Ca(NO3)2 was applied, until after net nitrification had ended on day 20. In contrast, Ca2+, Mg2+ and K+ were significantly more concentrated in the former treatment. This was probably caused by the greater concentration of anions that resulted from nitrification. P was always very dilute and unaffected by the form of N fertilizer. The form of N fertilizer had no significant effect on plant growth and nutrient uptake. The likely contribution of mass flow of the soil solution in supplying Ca, Mg and N to the plants was greatest when (NH4)2SO4 was supplied. The supply of K and P was unaffected by N fertilizer. The potential for N leaching loss was lower with (NH4)2SO4 than with Ca(NO3)2, especially up to day 20. However, the potential for cations leaching loss was greater in the (NH4)2SO4 treatment. This suggests that there is only a limited advantage in fertilizing with (NH4)2SO4 to reduce the total loss of nutrients from soil.     

Characterization of soluble lignin released from alfalfa by sheep digestion

A faecal soluble lignin fraction (FSL) extracted with 90% dioxane from the faeces of sheep fed on alfalfa hay was characterized by chemical analysis, nitrobenzene oxidation, fourier transform infrared spectroscopy and gel permeation chromatography, and compared with milled wood lignin (MWL) isolated from the alfalfa hay. The amount of FSL in the faeces was low, accounting for only 1% of the lignin present in the alfalfa hay. FSL and MWL consisted mostly of lignin components and contained a small amount of carbohydrate. FSL had a much higher proportion of syringylpropane units than MWL and showed a wide molecular size distribution. The results indicate the selective and limited solubilization of syringyl-rich lignin from alfalfa by sheep digestion.