Soil factors controlling Zn concentration in the corn plant are very complex, including among others a beneficial action of applied N and a detrimental action of P or lime inherently present or added to the soil. It is apparent that Zn deficiency is likely to be aggravated or created by row application at low rates or heavier mixed applications of readily available P fertilizer. The problem is greatest on soils that are calcareous and especially on those of high inherent P supply where plant Zn concentration already may be approaching a critical level. The more effectively the applied P is utilized by the crop, the more severe is the reduction in Zn utilization. Thus the calcareous soil with tendency for Zn deficiency perhaps should not be treated so as to afford maximum early uptake and utilization of applied P. It also seems evident that low P rates rather than heavy, infrequent applications are likely to give less damaging effects. Alternative to these procedures is to apply supplemental Zn whenever P is added to soil where the level of Zn availability is uncertain. The damaging effect of P on Zn utilization is considered to be largely physiological in nature, probably a plant root cell absorption phenomenon, and not an external Zn phosphate precipitation. It is recognized, however, that root proliferation in the band of row‐placed P may be a contributing factor due to inadequate exploration of a soil body where enough available Zn may exist.

High rates of fertilizer N used in many intensive farm management systems have been cited as a potential pollution hazard to surface and ground waters. The purpose of this study was to evaluate soil NO3− accumulations following 4 years continuous corn (Zea mays L.) grown with different nitrogen and irrigation regimes, and to compare these results to present NO3− concentrations found in irrigated farm fields of central and eastern Colorado. Soil NO3− content in the 300‐cm sampled profile was significantly influenced by both fertilizer N and irrigation treatments; the greater accumulations were associated with the two higher fertilizer N rates and two lower irrigation rates. Nitrate increased linearly in relation to fertilizer N between 67 and 269 kg N/ha and could be described by two simple regression equations separating the irrigation treatments into two groups (l‐2 and l‐3, low rates; l‐4 and l‐5, high rates). Coefficients of determination for the two groups were 0.981 and 0.975, respectively. Two hundred and seventy irrigated farm fields were sampled to a depth of 90 cm in central and eastern Colorado. Mean soil NO3−‐N content was 173 kg/ha and contents were not significantly different between coarse and fine textured groupings. Fields sampled immediately following beans (Phaseolus vulgaris L.) contained similar amounts as those following corn. Mean soil NO3− content decreased with greater soil depth. Observed NO3− concentrations appear to be the result of gradual accumulations from annual or near‐annual fertilizer N and/or manure applied over a period of time. Data from the 4‐year corn experiment clearly illustrate that NO3− can accumulate in a soil profile even when fertilizer N is applied at rates below that required for maximum production.

Greenhouse experiments were used to study soil compaction, moisture level, soluble P and Zn, pH, organic matter and clay contents, K saturation and titratable alkalinity as these soil factors influenced P‐Zn relationships in corn. Some of the resulting observations help to explain why starter fertilizers containing P may on occasions cause depressions in plant growth. Fertilizer P applied in the row markedly reduced Zn concentration of corn. Increasing soil compaction and soil moisture level caused further depressions of Zn concentration. The combination of irrigation practice on newly graded (and compacted) land, especially when soil P is high, would seem to portend Zn deficiency problems. Soil K saturation also appears to have a decided influence on P‐Zn relations in the plant. The higher the percent K saturation of the soil, the less did applied P reduce plant utilization of Zn in these experiments.

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