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While numerous studies have evaluated the efficacy of outdoor rainfall simulations to predict P concentrations in surface runoff, few studies have linked indoor rainfall simulations to P concentrations in surface runoff from agricultural fields. The objective of this study was to evaluate the capacity of indoor rainfall simulation to predict total dissolved P concentrations [TP(<0.45)] in field runoff for four dominant agricultural soils in South Dakota. Surface runoff from 10 residue‐free field plots (2 m wide by 2 m long, 2–3% slope) and packed soil boxes (1 m long by 20 cm wide by 7.5 cm high, 2–3% slope) was compared. Surface runoff was generated via rainfall simulation at an intensity of 65 mm h−1and was collected for 30 min. Packed boxes produced approximately 24% more runoff (range = 2.8–3.4 cm) than field plots (range = 2.3–2.7 cm) among all soils. No statistical differences in either TP(<0.45) concentration or TP(<0.45) loss was observed in runoff from packed boxes and field plots among soil series (0.17 < P< 0.83). Three of four soils showed significantly more total P lost from packed boxes than field plots. The TP(<0.45) concentration in surface runoff from field plots can be predicted from TP(<0.45) concentration in surface runoff from the packed boxes (0.68 < r2< 0.94). A single relationship was derived to predict field TP(<0.45) concentration in surface runoff using surface runoff TP(<0.45) concentration from packed boxes. Evidence is provided that indoor runoff can adequately predict TP(<0.45) concentration in field surface runoff for select soils.

A field experiment was established on a Sverdrup sandy loam in Central Minnesota to evaluate the effects of amounts and timing of nitrogen (N) fertilizer applications on N uptake by irrigated corn (Zea maysL.) and the movement of N into the aquifer 4.5 m below the soil surface. Nitrogen was applied as urea at rates of 179 and 269 kg N/ha in one application at planting or in split applications through the season. Soil solution analysis showed NO3moving below the rooting zone in all plots with much higher concentrations below the one‐time fertilizer applications. Split applications of N had only minimal effect on the concentration of NO3‐N in the aquifer but one‐time applications increased the concentration by 7 and 10 ppm. The use of 13N showed that splitting the 179‐kg rate increased the N in the plant derived from fertilizer from 33.1 to 54.5%, and increased the recovery of fertilizer N by the plant from 30.4 to 52.1%, even though whole plant yields were not affected. Nearly one‐fourth of the applied N remained in the upper 45‐cm soil layer at harvest regardless of treatment. No accumulation of NO3was found in the soil profile or underlying material to a depth of 3.0 m.

Cereal grain yield response to KCI fertilization has been reported on high K‐testing soils in the Northern Plains. Other field studies have demonstrated that wheat (Triticum aestivumL.) yield increases to CI fertilization occurred where disease incidence was high. Therefore, field experiments on high K‐testing soils were conducted over a 3‐yr period to determine the responsiveness of spring wheat, barley (Hordeum vulgareL.), and oats (Avena sativaL.) to KCI fertilization and to determine whether responses were due to K or to Cl. Experiments were conducted on soils representing Typic Argiustolls, Pachic Udic and Udic Haploborolls, and Pachic and Udic Haplustolls in eastern South Dakota. Spring wheat, barley, and oats showed grain yield increases (0.10 probability level) at four out of six, three out of six, and zero out of five sites, respectively, on soils that tested very high in ammonium acetate‐extractable K. Wheat grain yield increases varied form 0.2 to 0.5 Mg ha−1. Comparison of KCI, KNO3, and CaC12treatments, soil analysis, and plant analysis all indicated that the yield increases on very high K‐testing soils were due to the CI in the KCI and not due to the K. Six additional wheat experiments were conducted to determine the influence of starter K and CI (applied with seed) on grain yield; however, no yield increases to CI were detected in these studies. Both KCI and KNO3at a 20 kg K ha−1rate significantly decreased yield at one of six sites. Other experiments showed that if sufficient CI was present in the soil or broadcast applied, no additional benefit to seed placed CI occurred. Generally, broadcast and seed placed KCI appeared equally effective. However, rates required for maximum yield at several sites were too high to be placed in direct seed contact with drill application due to potentially adverse salt effects. Grain yield increases were large enough to make KCI fertilization of these soils very economical, provided responsive sites could be predicted.

Previous field studies have indicated yield responses of small grain crops to KCl on very high K‐testing soils, which were likely due to Cl fertilization. Suggested mechanisms for the involvement of Cl range from plant disease effects to effects on plant water relations. The possibility that climatic and biological environment may interact with the Cl response could make plant and soil diagnostic relationships difficult to interpret. The objectives of this study were to determine the relationships of plant tissue and soil Cl concentrations to hard red spring wheat (Triticum aestivumL.) yield, and to examine possible interactions with plant diseases and water relationships. Field experiments at 14 locations over 3 yr were conducted on Typic Argiustolls, Pachic and Udic Haplustolls, and Pachic Udic and Udic Haploborolls. A critical plant Cl concentration of 1.5 g kg−1for whole plants at head emergence assured 96% of maximum grain yield. Soil Cl levels > 43.5 kg ha−1(60 cm) or 75 kg ha−1(120 cm) were adequate for near‐maximum wheat yield. Both soil and plant Cl tests appeared to have potential as tools for diagnosing Cl responsive situations. Root and crown samples were taken at seven locations and rated for common root rot (Cochiobolus sativus). No influence of Cl on root rot was detected. Leaf rust (Puccinia recondita) and leafspot (complex of diseases) were suppressed at only one location by Cl addition. Leaf relative water content was measured at two locations and showed significant elvation due to Cl addition at both sites. The lack of detectable disease effects at some yield responsive sites and the good correlation between plant Cl concentration and yield response suggest that the beneficial effect of Cl was more general than disease reduction.