Biology of sandbur (Cenchrus schinatus L.) and its competition on corn at different nitrogen levels

Cenchrus species from different sources had similar burrs (fruit) and seeds except those from Polomolok which had burrs with thinner hulls and smaller seeds. Burrs had spiny hairs and contains two types of seeds- primary (larger seed) and secondary (smaller seed). Primary seeds germinated better than secondary seeds producing longer roots and shoots. Seeds sown in soil medium have higher germination percentage than sown in filter paper. A higher germination percentage was obtained from Cenchrus sown at 1 and 2 cm depth than sown at soil surface and at 4 cm depth. No germination was observed at 8 and 16 cm depth of sowing. Significant differences were observed in plant height, leaf area, number of tillers and branches produced and in dry weight. Polomolok ecotype was the tallest and had the largest leaf area and highest dry weight but the least number of tillers and branches produced. Matling ecotype was the shortest with the lowest dry weight but with the highest number of tillers and branches produced the same with ViSCA and UPLB ecotypes. Cenchrus flowered 32-41 days after emergence and seeds matured in 19-20 days. Burrs had 3 seeds. Polomolok ecotype had greater number of burrs per spike and Matling ecotype had the least number of burrs. Spike length were longer in the CMU and Polomolok ecotypes. Greatest number of spikes and seeds were from Matling, ViSCA and UPLB ecotypes. Handweeded (HW) corn with 90-30-30 kg NPK/ha were the tallest and had greater number of leaves, heavier and longer corn ears, higher fresh and dry weight and with higher NPK content. Unweeded (UW) corn with 60-30-30 kg NPK/ha had highest percent reduction in fresh and dry weights as well as in length and weights of corn ears; reduction in corn ear weight due to Cenchrus was 40.6 percent. Cenchrus in the unfertilized plots with 90-30-30 kg NPK/ha had greater number of tillers, burrs and spikes, longer spike length and with highest total NPK content in shoots and roots