Corn (Zea mays L.) grown in an equidistant plant‐spacing pattern (EPS) often yields more grain per unit area of land than that grown in conventional plant‐spacing patterns (CPS). The objective of this study was to determine the effect of equidistant plant spacing on aboveground dry matter production in corn. Two hybrids (‘Pioneer brand 3732’ and ‘B73 ✕ LH58’) were grown in two planting patterns (EPS and CPS) in field studies on a Chalmers silty clay loam soil (Typic Haplaquoll) near West Lafayette, IN, in 1983 and 1984. Measurements of plant dry matter accumulation and leaf area development began at growth stage V4 and continued weekly through R6. Growth analysis components were estimated from growth curves fitted to the relationships between the measured plant variables (dry weight per plant and dry weight per leaf) and a temperature index measured in growing degree days (GDD). Crop growth rate was greater for EPS than for CPS early in the growing season for both hybrids. An increase in plant biomass was primarily responsible. Although relative growth rate (RGR) tended to be smaller for EPS compared to CPS, the data suggested that the increase in plant biomass caused by EPS may be related to an increased RGR prior to 400 to 500 GDD after planting. Net assimilation rate was not significantly increased by EPS early in the season. Early and mid‐season leaf area indexes, however, were greater for EPS for both hybrids.

Accurate prediction of phenological development in maize (Zea mays L.) is fundamental to determining crop adaptation and yield potential. A number of thermal functions are used in crop models, but their relative precision in predicting maize development has not been quantified. The objectives of this study were (i) to evaluate the precision of eight thermal functions, (ii) to assess the effects of source data on the ability to differentiate among thermal functions, and (iii) to attribute the precision of thermal functions to their response across various temperature ranges. Data sets used in this study represent >1000 distinct maize hybrids, >50 geographic locations, and multiple planting dates and years. Thermal functions and calendar days were evaluated and grouped based on their temperature response and derivation as empirical linear, empirical nonlinear, and process-based functions. Precision in predicting phase durations from planting to anthesis or silking and from silking to physiological maturity was evaluated. Large data sets enabled increased differentiation of thermal functions, even when smaller data sets contained orthogonal, multi-location and -year data. At the highest level of differentiation, precision of thermal functions was in the order calendar days < empirical linear < process based < empirical nonlinear. Precision was associated with relatively low temperature sensitivity across the 10 to 26°C range. In contrast to other thermal functions, process-based functions were derived using supra-optimal temperatures, and consequently, they may better represent the developmental response of maize to supra-optimal temperatures. Supra-optimal temperatures could be more prevalent under future climate-change scenarios, but data sets in this study contained few data in that range.

season requirements of corn hybrids. Unfortunately, the days-to-maturity hybrid maturity descriptor most com-Delayed planting shortens the effective growing season for corn monly used by the seed industry, also called relative tween planting and BL decreased as planting was de-Purdue OARP Manuscript 16314.

Corn (Zea mays L.) grown at a given plant density often yields more grain per unit land area when the distance between adjacent rows is decreased and that between plants within a row is increased giving a more equidistant plant spacing pattern. The objective of this experiment was to determine whether hybrids or plant densities interact with the effect of 15‐in. row spacing on grain yield and stalk breakage of corn grown under nonirrigated conditions in Indiana. Two hybrids (Pioneer Brand ‘3732’ and ‘B73 × LH58’) were grown in field studies during 1984 through 1986 in two row spacings (15 and 30 in.) at four target plant densities (18 000, 24 000, 30 000, and 36 000 plants/acre) on three soils differing in yield potential. Across all nine environments, 15‐in. rows increased grain yields 4 bu/acre (or 2.7%) and percent stalk breakage 2.5% compared with 30‐in. rows. However, a significant (P ≤ 0.01) year‐by‐location‐by‐row spacing interaction was detected which indicated a strong dependence of the narrow row grain yield response upon local soil and climatic conditions. Grain yield increased in 15‐in. rows similarly in both hybrids, while stalk breakage increased significantly (4% more broken plants) only in the taller, later maturity hybrid B73 × LH58. A tendency existed for greater yield increases and smaller stalk breakage increases in 15‐in. rows at the lower, more adapted plant densities. The data suggest that optimum responses of grain yield and stalk breakage to 15‐in. rows may occur at plant densities which are adapted to a given location, rather than at greater than normal plant densities.

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