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

Abstract

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 (KNP), individual kernel weight (KW), grain yield per plant (GYP), andharvest index per plant (HIP); and (vi) enhanced per‐plant grain yield variability (GYCV). Genetic efforts to improve high plant density tolerance should, therefore, simultaneously focus on enhancing NUE and N stress tolerance.

Adapting maize crop to climate change

“…They reported considerably different profit-maximizing plant populations for the same hybrid across locations and/or seasons. For example, the profit-maximizing population of hybrid PR39W54 was 11.9 (2001), 17.5 (2002) In the research of Boomsma et al (2009), population interacted significantly with N availability, and lower populations were more suited to environments devoid of N. Over three years, per-area data gave OP(D) of 5.2 plants/m 2 for the low yielding 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 Growing season…”

“…Sarlangue et al (2007) reported optimum for HI populations of 12.7 plants/m 2 for hybrid Romario that exhibited the lowest PYP, 10.6 plants/m 2 for hybrid P37P73 with an intermediate PYP, and only 6.5 plants/m 2 for the highest yielding at low population DK688. Boomsma et al (2009) discovered that strong responsiveness of grain yield per plant to reduced plant crowding accompanies higher HI values and better nitrogen use efficiency, suggesting a relatively high level of reproductive partitioning and plasticity.…”

“…Cox (1996) discovered that different hybrids respond differently to plant population. In addition, the plant population at which hybrids achieve maximum grain yield has increased throughout the hybrid era (Duvick 1997(Duvick , 2005Tollenaar and Lee 2002;Boomsma et al 2009;Brekke et al 2011). In a similar manner, Widdicombe and Thelen (2002) stated that continued improvement in hybrid ability to tolerate stress from high crowding requires periodical reassessment of OP.…”

“…Indicatively, researchers working under greatly variable conditions found it hard to recommend a population (Norwood 2001;Blumenthal et al 2003;Shanahan et al 2004;Berzsenyi and Tokatlidis 2012). Such a problem is detectable even in studies under less variable environments (Farnham 2001;Popp et al 2006;Stanger and Lauer 2006;Tokatlidis et al 2011). Boomsma et al (2009 established the populations of 5.4 and 7.9 plants/m 2 deemed as suboptimal and optimal, respectively.…”

“…Maize grain yield increased from about 1,500 kg/ha in the early 1900s to 8,500 kg/ha at the beginning of the 2000s in the USA (Boomsma et al 2009;Assefa et al 2012). Despite this spectacular achievement, maize grain yield is closely related to plant population density (Van Roekel and Coulter 2011), and the crop suffers from an agronomic weakness of prime significance, affecting its grain productivity and stability.…”