Growth, yield components and micronutrient nutrition of field-grown maize (Zea mays L.) as affected by nitrogen fertilization and plant density
Growth and yield components in field-grown maize (Zea mays L.) were enhanced by nitrogen fertilization ranging from 50 to 200 kg N ha−1. Ear diameter, kernel depth, grain: stover ratio, number of ears plant−1, plant height and dry matter production increased as N fertilization rate was increased up to 100 or 150 kg N ha−1. Tasselling in maize was hastened by N fertilization. Increasing plant density from 25000 to 75000 plants ha−1 increased plant height, dry matter production and delayed tasseling but reduced ear diameter, kernel depth, grain: stover ratio and number of ears plant−1. Increased N supply and plant density had no influence on the concentrations of Mn, Zn, Cu, and Fe in ear leaf; except that Mn concentration increased as N fertilization rate was increased up to 150 kg N ha−1. Nitrogen × plant density interactions on the concentrations of the micronutrients in maize ear leaf were not significant.
Maize Morphophysiological Responses to Intense Crowding and Low Nitrogen Availability: An Analysis and Review
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 (GYp), 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.
The Performance of Insecticides – A Critical Review
As part of minimizing the risk of crop losses due to herbivorous arthropods (here, mainly referring to insects and mites), most of the World’s commercial food production systems are subjected to several applications of pesticides before being harvested. Some crops are sprayed 10-20 times, while most field crops are sprayed 1-5 times during the growing sea‐ son. In the US alone, the average number of insecticide applications ranges from 1-3 for most of the major field crops, and the total annual costs of pesticide applications exceed $1.3 billion ([1], U.S. Department of Agriculture agricultural statistics services: www.nass.us‐ da.gov/). Several large ag-producing countries publish extensive details on insecticide use, including Australia, and the data presented below were collected from a public website (http://usda01.library.cornell.edu/usda/nass/AgriChemUsFruits//2000s/2008/AgriChemUs‐ Fruits-05-21-2008.pdf) on pesticide applications in the US in 2006. A somewhat extreme but also important example is the fresh sweet maize production in the US, which was grown on about 85,000 ha. Based on data from 14 US states, 20 different active ingredients of herbi‐ cides were applied an average 1.04 times to fresh sweet maize and amounted to about 2.6 kg of active ingredients of herbicides per ha. The same data suggested that about 3.5 kg of 23 different active ingredients of insecticides were applied on average 2.10 times per ha. Simi‐ larly, tomato fields (grown on about 42,000 ha in the US in 2006) were treated with 12 differ‐ ent active ingredients of herbicides, which were applied, on average, 1.14 times and the equivalent of about 0.7 kg of active ingredients per ha. Regarding insecticides, the same to‐ mato fields were treated with 32 different active ingredients, which were applied an average of 3.6 times and equal to about 4.9 kg of active ingredients per ha. While tomatoes and sweet corn may be close to the top of the list of growing crops receiving pesticide treatments, cau‐ liflower, celery, and many other horticultural crops and fruits are also subjected to intensive pesticide spraying regimes. Thus, farmers acknowledge that weeds and arthropods can po‐ tentially cause significant economic losses, and total pesticide application costs are low