Studies on Competition between Upland Crops and Weeds

II. Comparison of early growth of crops

Abstract

The experiments reported here were designed to compare early growth on 4 species. of crops and 5 species of weeds typically in the Kanto plain. The experiments were conducted by changing the seeding time from April to July in 1971-72 years.
1. The plant height or main stem length on 30 days after seeding was the largest in corn, medium in upland rice and soybean. These were superior to weeds at the condition of the average of daily mean air temperature 13-25°C. Peanut was the smallest of crops, was equal to large crab-grass (Digitaria adscendens HENR.) at the condition of about 20°C, and was inferior to large crab-grass, common purslane (Portulaca oleracea L.) and Chufa (Cyperus microiria STEUD.) at the condition of about 25°C. The amount of extension of each plants was larger at high temperature condition, and the rate of extension by rising up the temperature was nearly equal in crops and the rate of weeds except Polygonum nodosum PERS. was larger than that of crops.
2. The top dry weight on 30 days after seeding was the largest in peanut, medium in corn and soybean. These were suprior to weeds at the condition of 13-25°C. Upland rice was the smallest of crops, was inferior to Polygonum nodosum PERS. at the condition of about 20°C, and inferior to Polygonum nodosum PERS., common purslane and large crab-grass at about 25°C. The amount of top dry weight was larger at high temperature condition, and the rate of increase in top dry weight of weeds by rising up the temperature was larger than that of crops. The high positive correlation between the top dry weight on 30 days after seeding and seed weight was observed.
3. The amount of increase in top dry weight of crops during 30 to 50 days after seeding was the largest in corn, medium in soybean and peanut, the smallest in upland rice. That of weeds was the largest in Polygonum nodosum PERS. which was superior to soybean, peanut and upland rice, besides superior to corn under about 22°C. That of large crabgrass, common lamb∋s-quarters (Chenopodium album L.) and common purslane was medium, but these were superior to that of upland rice. That of Chufa was the smallest of plants. The amount of increase in top dry weight was larger at high temperature condition, and the rate of increase by rising up the temperature was large in Chufa and large crabgrass.
4. As mentioned above, though growth of weeds from seeding to 30-40 days after seeding was inferior to crops, that of weeds from 30-40 days to 50 days after seeding was large, and competitive capasity to crops was extreamly elevated, especially at the condition of above 18-20°C. So, the weed control in early time is necessary, especially at higher temperature.