The influence of phosphorus fertilizers, population density and variety on growth, yield and root quality of carrot (daucuse arota Linn.)
The effects of phosphorus fertilizers (0, 92 and 184 kg P205/ha) and population density (666,666, 444,444 and 333,333 plants/ha) on the growth yield and root qu~litj of Nantes and Chantenay carrots were evaluated on the field plots of the University of Nairobi, Kabete, Kenya during the short and long rainy seasons of 1978 and 1979 respectively. The dry matter content of whole plants in the two cultivars increased as phosphorus fertilizer increased and population density decreased. However, the rate of dry matter accumulation in roots was faster than in shoots. Nantes generally accumulated a greater amount of dry matter than did Chantenay. The Efficiency of Storage Root Production (ESRP) increased as phosphorus levels increased and population density decreased. Nantes was more efficient in ESRP than Chantenay . Root yield (Plants and ha ) increased as phosphorus levels increased. Root yield plant increased but root yield ha-l decreased with a decrease in population density. Root yield (plant-l and ha-l) was higher in Nantes than in Chantenay. Population density did not have any effect on root length and diameter in the two cultivars. However, root length and diameter increased as phosphorus levels increased. Root length was longer in Nantes than in Chantenay but root diameter of the latter 'cultivar was larger than that of the former. All the two cultivars accumulated larger amounts of B- carotene in 1978 than in 1979. The amount of B- carotene produced in Nantes was greater than in Chantenay. Root B- carotene ha decreased but the amount root -1 increased as the population density decreased during the two years. Phosphorus fertilizers did not affect the accumulation of B- carotene in roots. Phosphorus fertilizers had no effect on the amounts of total 'and reducing sugars which accumulated in roots except that it increased the amount of total sugars per unit root fresh weight. Population density also had no effect on total an~ reducing sugars except that the amount root-l decreased with an increase in population density. Phosphorus fertilizers when applied to carrots grown in phosphorus - deficient soils containing high levels of soil moisture increased plant growth and root yield since phosphorus is an essential constituent of nucleic acid, phytin and phospholipids. Root yield beyond the optimum population density declined as a consequence of increased competition between plants. Efficiency of Storage Root Production (ESRP) in Nantes was greater than in Chantenay, since lower population densities and higher phosphorus levels resulted in the accumulation of greater amounts of dry matter in the former cultivar than in the latter. As a consequence, the root yield of Nantes was higher than that of Chantenay. Higher atmospheric temperature increased the amount of 8- carotene in roots probably by influencing the biosynthetic pathway of carotenoids (Yu-Heuy Chang et al., 1977). The size of ~oots was controlled by population density, cultivar and phosphorus ferti lizers. Nantes; the 30 x 10 cm spacing .and the 184 kg P205/ha produced the largest roots. Nantes at a population density of 444,444 plants/ha was found to be the best for the Central Province. Application of phosphorus fertilizers are recommended if only the level of this element in the soil is very low and when adequate soil moisture is available.