Effect of Nitrogen Fertilizer on Weeds Growth and Emergence and Yield and Yield Components of Corn (Zea mays L.)

Corn is one of the important crops of poaceae family which has important role in supplying food for human societies. Corn is third food crop in world and it has high potential compare to other crops because of its C4 photosynthetic pathway. In addition, corn is a strong and fast growing plant but it is sensitive to competition with weeds. According studies, there are 25 to 30 problematic weeds in corn farms which they include annual and perennial species. Annual weeds life cycle is similar to corn life cycle, there for the most problem of weeds in corn is summer annual weeds. Damage of weeds is different and it depends on weeds density, species composition, time of emergence, crop variety and other factors. While non control of weeds depending on those density and Variety, corn yeild may be decrease of 15 to 90 percent. Weeds which germinate in a short time can compete with crop on light, water and nutrition sources. Most of the weeds show better reaction to fertilizers compare with crops. This subject is due to weeds ability to nutrition absorption and aggregation and their high performances. Most of the weeds species are more responsive than crops to application of nitrogen fertilizer. Furthermore, the growth of most of the weed species increases with increasing nitrogen. Therefore, the increase of nitrogen in farming systems can have impacts on weeds and crops competitiveness. However, weeds compete with crop about using light, nutrient, water and soil space and the result of this competition is yield losses. Moreover, nitrogen is necessary to increase yield and nitrogen fertilizer enhances corn competitiveness, especially early in the season due to the slow growth of the plant and is necessary to achieve optimal performance. Excessive of nitrogen fertilizer during the growing season is benefit for weeds. Therefore, in order to study the effects of nitrogen fertilizer in combination with weeds management on yield and yield components of corn and weeds growth and emergence, a field study was conducted in research Station of Natural Resources Research Centre, Kerman province.
This experiment was conducted using a randomized complete block design with three replications. The treatments consisted of different levels of nitrogen in four levels (0, 80, 160, 240 kg ha-1) urea fertilizer (46%). In addition, for assessment the effect of experimental treatments, each plot separated into two parts (complete control and non-control of weeds). Preparing the field was done with autumn plowing and spring disc. Corn seeds (single cross 704) were planted on rows in the spring with hand and with the density of 71000 plants per hectare with row spacing of 70 cm and 20cm. Irrigation was performed on average every7 days. Weeds in the control treatment were weeding by hand twice during the growing season.
The results showed that nitrogen application in combination with weeds control increased yield and yield components of corn and the other growth traits, significantly. The maximum corn yield observed 12/8 kg under high nitrogen treatment (240 kg ha-1) with 88/82% increase compare with non-fertilizer treatment. Moreover, increase in nitrogen imposed a significant positive affect on height, yield and yield components including (Length and ear diameter and ear dry matter, the number of grains in row and the number of rows in ear, hundred grain weight). Nitrogen is one of the factors affecting the development of leaf area per plant and therefore, the development of the corn canopy. It seems that the increase of nitrogen during the tassel stage and seed formation which are the most sensitive stages to nitrogen absorption and photosynthesis, increased the length of ear. In addition, results of the experiment indicated that control of weeds had significant effect on different growth factors. Furthermore, the increase nitrogen rate caused to weeds emergence rate and dry weight increase. The greatest dry weight of weeds was observed at the highest level of fertilizer (240 kg ha-1). It can be said that in the latter stages of growth that competition was effected and caused dominance strong species, increasing fertilizer after a certain amount (160 kg ha-1) had no effect on the dry matter competing species in the field. Therefore, it seems that competition in the early stages is very important.
C4 weeds such as Barnyard grass and Slender foxtail and Redroot pigweed, showed more growth increase compare with C3 species. Therefore, C4 species are more dominance than C3 species in competition and increased germination rate for these weeds with increasing nitrogen rate. As a result, we should control these weeds early in high nitrogen rate. So, nitrogen fertilizer had positive impact at different forms on the plants, resulting in the use of this nutrient should be done more researches.