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Plant samples were taken from a forty‐acre field in an 82.5 ft. grid at two sampling dates each year during a three‐year study. Soil samples were also taken in the same grid. Potassium (K) was analyzed in the plant samples using both a strong acid‐digest and a dilute (2%) acetic acid extraction. Plant K analyzed using both techniques were correlated with soil test K levels. Plant K analyzed with acid‐digestion was also highly correlated with the acetic acid‐extracted K. Mapping of early sampled plant K better represented soil K level patterns than later sampling. Plant K maps described areas of low K not represented by soil K level maps. Plant analysis may be useful in mapping areas for relative K nutrition where soil K analysis is not as descriptive of plant response to fertilizer K.

A long‐term (1968–1987) field study using corn‐soybean in rotation was conducted to compare the effect of rock phosphate (RP) and superphosphate (SP) at two lime levels on crop yield, soil availabl...

Variable rate fertilizer application being commercially performed today is most often based on a soil test map. The sampling density used to develop a map is often selected without background information regarding field soil test variability. The objective of this study was to determine how many samples should be taken from a field in order to locate and describe major areas of fertility affecting variable rate fertilizer applications. Two 40 acre fields were sampled in an 82.5 ft grid each fall from 1989 to 1992. Soil pH, Bray P1, and available K levels were determined on each sample and maps were made using inverse distance squared estimates. Data were taken from the samplings to represent a 165 ft and 330 ft grid pattern. Maps were developed from these less dense grids and compared with the 82.5 ft grid values. In 1992, a separate 220 ft grid sampling was taken. The 220 ft grid estimates were more highly correlated with the 82.5 ft grid values than were the 330 ft grid estimates, however, membership of 220 ft and 330 ft grid estimates within soil test categories were similar. Fertilizer P and K applications were made in one field following the 1992 sampling. Spring 1993 sampling showed the success of the 220 ft grid in directing a variable rate application of P and K. Comparisons to theoretical P and K applications directed by a 330 ft grid map showed the superiority of the 220 ft grid compared with the 330 ft grid.

Plant samples were taken in an 82.5 ft grid at an early and late sampling date in both 1991 and 1992 from a forty acre field in Illinois. Calcium (Ca) and magnesium (Mg) were analyzed on each sample and maps were made showing the levels of each nutrient within the field. Soil pH measurements were also made from each of the same sampling locations following each year of plant sampling. In the fall of 1991, a calcitic lime application was made using soil pH informations from the 1991 soil sampling to determine the boundaries and rate of the application. Calcium and Mg levels in 1991 roughly defined the area of low pH, except for the early sampled Mg levels. However, low Ca and Mg levels did not always indicate low pH levels. High Ca and Mg levels did not always indicate high pH levels. Following liming, plant Ca levels correlated better with soil pH and represented areas of high and low pH better than plant Mg. Other factors which influenced Ca and Mg levels may have been high levels of competitive...

Following a favourable crop response to rock phosphate (RP) in a long term fertility trial in DeKalb, IL, an experiment was designed to dissolve RP in silage leachate on the premise that silage has a pH of 4.0 to 4.2 and that once drained of its leachate, it can be used for animal feed. Two types of RP, Brown Sugar RP and Ruhm's RP, having 30% P2O5 were dissolved in pure organic acids similar to those present in silage leachates. The amount of dissolved phosphorus (P) from RP in organic acids increased with organic acid:RP ratio. The highest amount of P dissolution was found with butyric acid. Thus, butyric acid with Brown Sugar RP, 2519, 1500, and 710 μg P/g RP were dissolved at 800, 400, and 200 acid:RP ratio, respectively; with Ruhm's RP the values were 3900, 1988, and 835, μg P/g RP, respectively. After dissolution of the two types of RP in the acids, there was an increase in solution pH of 1 to 2 units. Of the three types of silage leachates used, grass silage leachate had the highest acidit...

Monocropping and long-term use of highly water soluble commercial fertilizers may reduce crop yields and contaminate surface and ground water. A long-term experiment compared the effectiveness of rock phosphate (RP) with superphosphate (SP) on crop yields, soil tests, and leaf nutrient concentrations in two rotations with or without addition of N or lime in a strip-block design with phosphate as vertical factor and N or lime as horizontal factor applied over P treatments. Crops in rotation A (1952–1967) included oats (Avena sativa L.), alfalfa (Medicago sativa L.), corn (Zea mays L.) 1st yr and corn 2nd yr while crops in rotation B (1968–1983) included corn and soybean (Glycine max L.). Phosphate application as single source, RP and SP in combination, and RP with elemental sulphur ranged from 0 to 40 kg P ha−1 yr−1. In rotation A, RP was applied once every 8 yr at eight times the annual rate; in rotation B it was applied at half the annual rate of rotation A. The SP was applied annually in both rotations. In both rotations, P treatments significantly increased crop yields. In rotation A, crop yields on RP treatments were similar to those on corresponding SP treatments except for oats. Similarly, yields of crops grown with RP alone were similar to those obtained with a mixture of RP with SP or S. But corn grown after alfalfa did not respond to N application nor did crop yields respond to lime application. In rotation B, at low lime, corn and soybean yields were similar on RP treatments to those on corresponding SP treatments, but at high lime, yields were significantly lower with RP than corresponding SP treatments. Further, crop yields on mixture of RP and SP were similar to yields with RP alone, and the RP and S combination produced lower soybean yields and similar corn yields than RP alone. In this long-term cropping sequence study, on acidic soil RP was equally as effective as SP in supplying P to crops. Key words: Rock phosphate, superphosphate, legumes, lime, nitrogen

Soil testing is viewed as the application of Soil Science Research. Thus, the history of soil testing is interwoven with the growth and development of soil science. Soil testing as a recognized sub‐unit of soil science emerged in the early 1940's with agriculture's transition from subsistence to production farming systems. Soil testing today enjoys popularity in direct relation to the research data base and the extent to which the crop production limiting soil factors are manageable and ameliorating materials are available at a reasonable cost.

The relationship between soil K, fertilizer K, plant K, and plant Mg was investigated at three sample periods. A statistically significant linear correlation between variables vas observed. Simple correlations between soil K vs plant K and fertilizer K vs plant K were positive, and simple correlations between soil K vs plant Mg, fertilizer K vs plant Mg, and plant K vs plant Mg were negative in all sample periods. It was shown that there is a possibility that Mg may be limiting corn yields when plant K is at the critical percentage derived under the conditions of this experiment.

A P x K fertilizer experiment with five soybean cultivars was conducted to evaluate possible differential response of the different cultivars to moderate rates of fertilizer. Significant effects of fertilizer upon yield and leaf composition were observed in different years, suggesting possible interactions with other environmental variables. Significant differences in nutrient content of leaves and soybean seed were attributed to cultivar effects. The effects of P and K upon nutrient content of the seed differed among cultivars.

ABSTRACT According to the capacitor model, the potential development of membrane electrodes is the result of adsorption of ions or charged particles on the electrode surface forming a double layer and capacitor. Our results differ from those previously reported in that the adsorption of charged particles at the pH glass electrode interface is the main cause of the suspension effect rather than the reference electrode effect. Charged particles, if adsorbed on the SCE tip opening, may cause minor suspension effects on the reference electrode potential. Our results have demonstrated how previous investigators misused the H+-form exchange resins in the suspension effect study, ignoring the exchange reaction between the H+ ion and K+ ion. The pH glass electrode, antimony electrode and lead electrode and ion exchange resin, activated carbon, graphite and silica gel were used in the study.

Soil samples were obtained at 0–3, 3–6, 6–9 and 0–9 inch depths from experimental plots receiving five tillage treatments. Each of two samplers composited approximately six one‐inch cores from each plot. Soil samples were analyzed for acidity, P and K using routine analysis procedures in the University of Illinois Soil Testing Laboratory. Few significant differences were attributed to sampler and it was concluded that samplers using similar sampling techniques were obtaining soil samples from the same population. No significant differences in soil acidity at different depths were observed. The different tillage methods did significantly affect soil P at the 0–3 inch depth, but had no significant effect on soil P at deeper depths. Different tillage methods also significantly affected soil K values at different depths.

Corn yields and leaf samples were obtained from experimental plots receiving varying rates of N, P, and K. Yields were placed in two groups. One group consisted of yields < 134 bu/A, and a second group consisted of yields ≥ 134 bu/A. Within each group yields were regressed on leaf levels of N, P, K, Ca, Mg, B, Cu, Fe, Mn and Zn as independent variables in a second order polynomial. Using stepwise regression procedures the fit of the polynomial was determined for each set of observations, and statistical significance of various effects was determined. The regression accounted for 71.5 percent of observed variability in yields in the < 134 bu/A category, and 53.2 percent of observed variability in yields in the ≥ 134 bu/A category. With statistical criteria used, twelve interactions were observed in both groupings, but the PFe interaction was the only one common to both analyses. Seven interactions with Mn were observed in the lower yield category, but only one in the upper category. One linear eff...

Corn yields and leaf samples vere obtained from experimental plots receiving various rates and combinations of N, P and K. Yields were regressed on leaf N, P, K, Ca and Mg as independent variables expressed in milliequivalents per 100 grams and percentages in three regression models. The fit of two models was shown to be equivalent regardless of method of expressing the independent variables. For the other model the choice of milliequivalents per 100 grams or percentages determines a unique function.

Plant analyses can be a powerful tool in the diagnosis of yield depressions. Critical plant composition data for corn, soybeans, wheat, and alfalfa are presented which can be useful in interpreting plant analyses. Data are also presented to indicate “normal” variations that may be expected to occur in plant composition resulting from variations hi varieties, seasons and soil. For the corn plant, the nutrient composition of some elements change with the leaf sampled and the maturity of the plant.

The effect of animal activity and fertilizer practices on the nitrate content in soils with and without natric horizons was investigated in a field study in southern Illinois where excessive ground-water nitrate levels were reported. Most of these soils are poorly drained. A comparison is provided by the poorly and well-drained soils without natric horizons observed in central Illinois. The results indicate that soils with natric horizons at shallow depths or dark-colored poorly drained soils had low levels of nitrate in the profile; all other soils showing increased nitrate levels in the entire profile or below the root zone were related to the amount of fertilizer used or the amount of animal activity. Animal operations resulted in larger amounts of nitrate in similar soil profiles than did fertilizer applications. Increased nitrate content of the ground water, sampled in Washington County, similarly was related to fertilizer practices and animal activity in all soils, except under soils with natric horizons at shallow depths.

The relationship between corn yield and nutrient composition of whole plants at two stages of growth, and between corn yield and nutrient composition of different plant parts at early tassel was investigated. It was found that chemical composition of plants about 10 inches in height was more closely associated with yield than chemical composition when plants were about 30 inches high. Chemical composition of lower stalk or lower leaves was more closely associated with yield than was the composition of other plant parts.

Corn yields and leaf samples were obtained from experimental plots receiving varying rates of N, P and K. Yields were regressed on leaf levels of N, P, K, Ca, Mg, B, Cu, Fe, Mn and Zn as independent variables. Various polynomial regressions were fitted to the yields and “goodness of fit”; of particular mathematical models was used as a basis for evaluating particular biological and statistical concepts. It was found that no regression, where chemical elements were used as ratios, fit the observations as well as a quadratic polynomial or its square root transformation. This suggests that within the set of data used, emphasis on particular cation or anion ratios does not necessarily result in the “best”; explanation of variation in yield. “Classical”; growth equations were fitted to corn yields, but were not as precise in predicting yields as the polynomials. A modified stagewise regression procedure was used for fitting one mathematical model, but results were less satisfactory than those obtained...

Thirty‐two years after the addition of high rates of potassium to two Illinois experiment fields, the largest gain in soil K was in the acid‐insoluble form. Cation exchange capacity of the soil clays had decreased with the increasing addition of K, presumably due to fixation of potassium in the interlattice positions of clays. An X‐ray diffraction analysis did not provide any conclusive evidence as to the formation of illitic minerals.

Mesure de la capacite d'echange des cations pour le chaume, en fonction des echantillons de Poa pratensis utilises et du pH