No description available.

No description available.

Maize production in short-season environments has at least two critical problems. Firstly, maize grown in short-season areas has lower leaf area indices (LAI) than maize grown in long season areas, due to shorter plant stature and less time for development, which results in reduced leaf number and size. Secondly, in very short-season areas the seasonal thermal-time available may be insufficient to mature grain of current maize hybrids. Therefore development of maize types that accumulate leaf area and mature quickly would increase production of maize in mid- to short-season areas. The leafy (Lfy1) and reduced-stature (rd1) genes make contributions to this end. However, these two genes have not previously been combined. From 1991 to 1993, field experiments were conducted to evaluate the leafy reduced-stature (LRS) inbred lines and hybrids for yield, maturity times and morphological traits, at different planting densities and patterns in Montreal and Ottawa. LRS maize inbred lines showed the most rapid silk extrusion, optimum leaf area development, and rapid growth of the first ear, the highest yield per unit leaf area, and the closest synchronization of pollen shed and silk extrusion at high plant population densities. LRS maize hybrids had the most rapid leaf development, longest grain filling period, lowest grain moisture content at harvest, and highest harvest index. Therefore LRS hybrids should allow an extension into shorter season areas where it can not now be successfully cultivated, and may increase yields in mid- to short season areas where maize is now produced.

The objectives of this study were to evaluate the effects of earlier corn (Zea mays L.) harvest, on corn yield, intercrop growth, and soil N levels, and to evaluate the effects of red clover (Trifolium pratense L.) compared to ryegrass (Lolium multiflorum Lam.) as intercrops on corn yield and soil N levels. / After two years, earlier corn harvest did not result in greater intercrop growth or higher soil N levels compared with later corn harvest and there was no significant soil N contribution by legume intercrops in either harvest period. Thus, no soil N benefit was found from using intercrops in earlier harvest for silage compared to later harvest for grain corn, nor from using red clover compared to ryegrass as an intercrop. / In the early harvested silage system, a quadratic corn yield response to added N suggested that near-maximum corn dry matter yields were obtained at the rate of 140 kg N ha$ sp{-1}$. Maximum total dry matter yields were not obtained in the late harvest grain system in any site-year. Legume and non-legume intercrop species had similar effects on corn yield.

Thesis (D.Phil.(Agricultural extention))-University of Pretoria, 2007. / Includes bibliographic references (leaves 191-199).

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The yield of short-season hybrids is lower than long-season hybrids, mainly as a result of the low final leaf area developed by the short-season plants. This is due to the smaller plant stature and smaller leaf number and size of short-season adapted hybrids. In addition, in short-season areas the thermal-time available may be insufficient to mature grain of current maize hybrids. Maize hybrids which accumulate leaf area quickly, mature earlier, yield well and tolerate higher population densities better than the currently available hybrids would be more suitable for production in short-season areas. The "Leafy reduced-stature" maize hybrids, which have only recently been developed, have traits which address these criteria. There has been no previous effort to evaluate the effects of more than two plant population densities or the effects of planting patterns on the yield, yield components and vegetative growth of these hybrids. in 1995, field experiments were conducted at two sites near Montreal to compare the response of leafy reduced-stature (LRS), non-leafy normal stature (NLNS), and non-leafy reduced-stature (NLRS) maize hybrids to plant population densities and planting patterns. LRS maize hybrids showed the most rapid growth of the first ear, and the highest yield per single plant and per hectare at high plant population densities in paired rows. LRS hybrids also had longer grain filling periods, lower grain moisture contents and higher harvest indices than conventional (NLNS) hybrids. Rapid growth of the first ear and a higher harvest index are indications that LRS hybrids should be more tolerant of higher population densities than currently available hybrids. Therefore, LRS hybrids show promise for production in short-season areas at high plant population densities where maize cultivation is not currently economical due to shortness of the growing-season.

Nitrogen fertilizer use suffers from low efficiencies and increased residual NO$ sb3$ in the soil. The purpose of this study was to compare N fertilizer efficiency by a comparison of three N sources, three rates of N fertilization, and three application times of N fertilizer. Grain corn yields increased with increases in N rates, and split applications of N were superior to preplant incorporated (PPI) fertilizer. Grain N uptake was associated to grain yield and N uptake. Stover yields increased with increased N and varied with application times of N, but the effects were not as pronounced as with grain yields. Soil NO$ sb3$ generally increased with increases of added N but not with split application of N compared to PPI N. Soil NO$ sb3$ in the spring in control plots was related to grain yield response to added N but not to stover yield response.

No description available.

No description available.