Growth and nutrient uptake by cotton roots under field conditions

The relationship between nutrient uptake and root growth of cotton (Gossypi um hirsutum L.) was studied under field conditions. This basic information could be beneficial when making best management decisions concerning the ti me of application and placement of fertilizer. A field study was conducted in North Alabama on a fertile Dewey silt loam (clayey, kaolinitic, thermic Typic Paleudult). Aboveground whole plants were harvested at approximately 10-day intervals beginning at 211 cumulative heat units (CHU) after plantin g (37 days after planting: 4-true leaves). Root length of harvested plants was also measured by depth and distance from the plant. Maximum root length was obtained at 1174 CHU (117 days after planting), while dry matter conti nued to increase until a maximum was obtained at 1317 CHU (128 days after p lanting). Maximum root length density of 1.60 cm cm(3) was obtained in the surface 0-15 cm layer in the in-row position at 912 CHU (99 days after plan ting). After first bloom approximately 70% of the cotton root system was in the surface 30 cm of soil. Average daily influx of S per m of root length increased with plant age until 1317 CHU (near cut-out), after which influx declined. Nitrogen (N), calcium (Ca), and iron (Fe) influx peaked very earl y in the season (291-469 CHU) followed by a general decrease with plant age . Maximum daily influx of potassium (K), phosphorus (P), magnesium (Mg), co pper (Cu), manganese (Mn), and zinc (Zn) per meter of root occurred at appr oximately peak-bloom (764-912 CHU, 87-99 days after planting) and decreased with plant age. Copper, Fe, Mn, and Zn influx rates were similar or equal to 1000 times lower as compared to the other nutrients.