A method for the determination of S in plant materials is described. The material is oxidized by nitric and perchloric acid using a heating block to reduce perchloric acid loss. The SO 4 content of the solution is determined turbidimetrically as BaSO 4 . The proposed method has been found to be more accurate and rapid than the conventional dry ashing procedures for the determination of S in plant material.

Deficiency of S in soils has become a soil fertility issue worldwide because of a decrease in S deposition from air to soil due to legislation and increased crop removal. Continuous use of high‐analysis nitrogen/phosphorus (NP) fertilizers lacking in S further exacerbates the S deficiency for crop production. Several newly developed granular NP fertilizers such as monoammonium phosphate (MAP), diammonium phosphate (DAP), and triple superphosphate (TSP) containing micronized elemental sulfur (ES) with/without ammonium sulfate (AS) have been marketed to farmers. It is claimed that these products can provide available SO4–S through AS and ES oxidation during the growing season. The objective of this review was to carefully examine the literature that addresses the agronomic effectiveness of the granular NP–ES or NP– (ES+AS) fertilizer products. The review shows that oxidation of ES particles in granular NP fertilizers is generally nil or inadequate to provide available S to seasonal (or first) crops in greenhouse studies. This is due to the negative locality effect on granular ES oxidation. In contrast, available S can be obtained from the associated AS component of the granular (ES+AS). Under field conditions, limited studies showed these granular (ES+AS) were as effective as SO4–based sources at a high single S rate, but lack of data at multiple S rates. The detailed evaluation of available data so far often shows that the granular NP fertilizers containing ES or (ES+AS) cannot provide available S as compared with traditional SO4–based S sources for season‐long or first field crops. Sulfur nutrient is important to crop growth to produce maximum crop yield. Several new S fertilizers are marketed to farmers often without scientific data to support the fertilizer producers’ claims. This review article examines the available data to check the claims; the results often cannot validate the claims.

Year‐to‐year consistency of crop yields within a farm field is needed to use grain yield monitor data for site‐specific management decisions such as yield goals for fertilizer recommendations. A 5‐yr study was conducted from 1991 to 1995 to determine whether patterns of corn (Zea mays L.) grain yields are similar over a number of years and whether grain yields from one or more years can be used to predict grain yields for subsequent years. The experimental site was located at the Northern Cornbelt Sand Plain Management Systems Evaluation Area near Princeton, MN. The research area was 4.4 acres with soils mapped as three variants of the Zimmerman fine sand (mixed, frigid, argic, Udipsamment) and a Cantlin loamy fine sand (sandy, mixed, frigid, typic, Udipsamment). Continuous corn was grown from 1990 through 1995 after alfalfa (Medicago saliva L.) from 1981 through 1989. Cultural practices were applied uniformly to the 4.4 acre site each year. The 4.4 acres were divided into 60 grid cells (50 ft. by 60 ft.) and grain yields, corrected to 15.5% moisture, were determined by hand harvesting an area (two rows 20 ft. long) within each of the 60 grid cells. Differences between highest and lowest continuous corn grain yields in the research area were 72 bu/acre in 1991, 44 bu/acre in 1992, 45 bu/acre in 1993, 51 bu/acre in 1994, and 57 bu/acre in 1995. Grain yields were not spatially consistent from year to year. Areas with better grain yields were not consistent from year to year, and conversely, poor production areas were not found in similar locations each year. Only 4 to 42% of the grain yield variability for a given year is accounted for by a knowledge of the grain yields from a previous year. The lack of grain yield stability as measured by ranked correlations on a sandy soil raises serious questions for the potential for use of this information. The data indicate that the use of grain yield maps for fertilizer recommendations on a site specific basis may not be possible or may require a much longer term database than the normally recommended 5 yr, unless there is a construct of inputs that explains the grain yield patterns each year. Research Question With variable rate technology it is possible to make changes in the application of crop production inputs on the go. Fertilizer recommendations are often adjusted for yield goal. Therefore, it is important to have some measure of consistent yield patterns across a landscape. Are differences in yields across a field consistent over time? Can measured differences in yield be used to established more realistic yield goals? Literature Summary Growers usually know that certain areas of their production fields produce more yield than others. Until recently, the technology to measure and locate the variability of yields has not been available. Yield goals have been used to develop fertilizer recommendations in the Upper Midwest. Before the development of yield monitoring technology, yield goals were usually based on production information from entire fields. Now yield goals ...

creases. A primary factor reported for predicting a yield response is soil inorganic N concentrations early in the Predicted physiological factors and a limited number of field studies growing season. Positive increases in soybean yields have resulted in debate regarding the recommendation of in-season fertilizer N for soybean [Glycine max. (L.) Merrill]. The objective from supplemental N applications are a function of soil of our research was to evaluate several in-season N fertilization strate-N concentrations (Stone et al., 1985). They concluded gies on soybean seed yield response as well as to measure the effect that fertilizer N increased soybean yields only if preplant of fertilizer N additions on late-season plant N concentrations and soil NO 3 -N concentrations were Ͻ190 kg ha Ϫ1 in the accumulation, seed N removal, seed protein, and seed oil composition. top 180 cm. Al-Ithawi et al. (1980) measured significant The research was conducted at 12 sites in the southern soybeanseed yield increases at all three sites in one year and growing region of Minnesota in 1998 and 1999. A combination of (i) only at a moisture-limiting site in a second year. They application time (July vs. August), (ii) placement method (broadcast attributed the yield response to inadequate residual soil vs. knifed), and (iii) N source (urea vs. poly-coated urea) gave five NO 3 -N at planting for the responding sites in Nebraska. N treatments plus a control at all sites. Seed yield did not respond toIn addition to soil N status, Lyons and Earley (1952) the fertilizer N treatments at any of the 12 sites; however, a combined analysis indicated a significant increase (generally less than 0.06 Mg suggested that soybean response to either plowdown or ha Ϫ1 ) from using polymer-coated urea or applying the urea in August. topdressed N is dependent on rainfall and temperature Herbage dry matter (DM) and herbage N concentrations at the R6during the growing season because these environmental stage were not affected by any of the N fertilizer strategies. Although factors influence sufficiency of symbiotically fixed N. soybean seed protein was statistically different among the treatments, Seed yield increases were not obtained with N rates protein was only increased 0.4 g kg Ϫ1 . Soybean oil concentration was up to 448 kg ha Ϫ1 in Illinois (Johnson et al., 1975). In not affected by fertilizer treatments. In general, polymer-coated urea, Iowa, preplant N applications up to 270 kg ha Ϫ1 did knifed applications, and August applications increased soil NO 3 -N not affect seed yields (Bharati et al., 1986). Beard and in the 0-to 30-cm layer at R6 relative to standard urea, broadcast Hoover (1971) also found no soybean seed yield reapplications, and July applications. Even though in-season N fertilizer sponse to a series of N rates under irrigation in Califorcreated greater levels of available soil N at all 12 sites during soybean pod filling, seed yield was not improved compared with unfertilized Abbreviations: DM, dry matter. Published in Agron. J. 93:98...

Philosophical differences exist in the interpretation and recommendations made from soil test values acquired by different organizations that provide advice to farmers on fertilizer use. It was the objective of this study to evaluate the economic and agronomic impacts of these varied philosophies with particular reference to concepts of cation ratio, nutrient maintenance, and nutrient sufficiency level. Field experiments were conducted during 1973–1980 on four major soils of Nebraska comparing yields of corn (Zea mays L.) grown with fertilizer treatments as recommended by five soil testing laboratories operating in the state. The 29 field comparisons revealed no real yield differences despite wide variation in number, rate, and cost of nutrients applied. Since soil test levels are increasing or at least holding steady with the “nutrient sufficiency” approach to soil testing, we find no economic or agronomic basis for the “balance” or “maintenance” concepts on these representative soils of the western Corn Belt. Not to be overlooked are environmental implications nor the waste of energy and resources from any approach responsible for excessive fertilizer use. It is recognized that reserves of available nutrients in the deep subsoils and underlying soil‐forming materials in this region have a substantial bearing on soil test calibration and that different calibrations may exist with less favorable subsoil rooting conditions.