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Maize Morphophysiological Responses to Intense Crowding and Low Nitrogen Availability: An Analysis and Review

^a Dow AgroSciences, 2310 County Road/1050 North, Homer, IL 61849
^b Agronomy Dep., Purdue Univ., 915 W State Street, West Lafayette, IN 47907-2054
^c Dep. of Plant Agriculture, Univ. of Guelph, Guelph, ON N1G 2W1 Canada

^* Corresponding author (tvyn{at}purdue.edu).

Mounting concerns over the cost and environmental impact of N fertilizer combined with progressively higher plant densities in maize (Zea mays L.) production systems make progress in maize N use efficiency (NUE) and N stress tolerance essential. The primary objectives of this 3-yr field study were to (i) evaluate the N responsiveness, NUE, and N stress tolerance of multiple modern maize genotypes using suboptimal, optimal, and supraoptimal plant densities (54,000, 79,000, and 104,000 plants ha^–1, respectively) with three levels of side-dress N (0, 165, and 330 kg N ha^–1), (ii) identify key morphophysiological responses to the simultaneous stresses of intense crowding and low N availability, and (iii) consider our results with extensive reference to literature on maize morphophysiological responses to plant crowding and N availability. At optimal and supraoptimal plant densities, maize receiving 165 kg ha^–1 of side-dress N displayed strong N responsiveness, high NUE, pronounced crowding tolerance, and plant density independence. However, crowding tolerance was contingent on N application. Relative to less crowded, N-fertilized environments, the 104,000 plants ha^–1, 0 kg N ha^–1 treatment combination exhibited (i) reduced pre- and postanthesis plant height (PHT), stem diameter (SD), and total biomass; (ii) greater preflowering leaf senescence and lower R1 leaf areas at individual-leaf, per-plant, and canopy levels; (iii) enhanced floral protandry; (iv) lower pre- and postanthesis leaf-chlorophyll content; (v) lower per-plant kernel number (KN_P), individual kernel weight (KW), grain yield per plant (GY_P), andharvest index per plant (HI_P); and (vi) enhanced per-plant grain yield variability (GY_CV). Genetic efforts to improve high plant density tolerance should, therefore, simultaneously focus on enhancing NUE and N stress tolerance.

Abbreviations: ACRE, Purdue University Agronomy Center for Research and Education • ASI_P, per-plant anthesis–silking interval • b, a coefficient that describes the breadth/kurtosis of the distribution of green leaf area • GDD, growing degree days • GY_A, per-unit-area grain yield • GY_CV, per-plant grain yield variability • GY_P, per-plant grain yield • GY_SA, per-plant sampling area grain yield • HI, harvest index • HI_P, per-plant harvest index • KN_P, per-plant kernel number • KW, individual kernel weight • LA_D, per-plant green leaf area distribution • LA_n, fully expanded individual leaf area • LA_P, per-plant green leaf area • LÁ_T, per-plant green leaf area of tagged, nondestructively sampled plants • LAI_G, green leaf area index • NL_T, total number of green leaves per plant • N_R, nitrogen application rate • NUE, nitrogen use efficiency • PDA, personal digital assistant • PHT, plant height • PPAC, Pinney-Purdue Agricultural Center • SD, stem diameter • SPAD, single-photon avalanche diode • TB_P, aboveground per-plant total biomass • VB_P, aboveground per-plant vegetative biomass • x_e, earleaf position • x_H, position of the highest green leaf • x_L, position of the lowest green leaf • x_o, position of the largest leaf

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Received for publication February 27, 2009.