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Root Growth and Nutrient Uptake Characteristics of Some Cowpea Varieties¹

Efficient utilization of fertilizer P and K by a crop depends, to a large extent, on the amount of roots that contact the fertilizer nutrient, as well as the capacity of the root to absorb the contacted nutrient. In order to find a Nigerian cowpea that utilizes soil and applied nutrients best, five cowpea cultivars commonly cultivated in Nigeria were grown in fertile and N, P, and K deficient soils in the greenhouse. Specific objectives were to determine differences in root growth (length) and nutrient uptake efficiencies of roots (µg/m) among the five cultivars.

To determine the effect of age on the ability of a cowpea plant to utilize soil nutrients, cowpea cultivar ‘H113–4’ was grown for 30 days in solution culture and changes in root length and nutrient uptake rates (µg/m-day) as functions of plant age were evaluated. When grown in fertile soil, ‘Ife-brown’, H113–4, and Westbred cultivars had significantly greater root lengths (17.5, 17.2, and 16.7 m respectively) than ‘1534’ (14.3 m.); while ‘Crimson's’ root length (15.4 m) was intermediate. In the N-P-K- deficient soil, however, Crimson had the most extensive root system (19 m). Apparently, H113–4 had the greatest total uptake of P, K, and Ca (9.9 mg), K uptake efficiency (360 µg K/m root length), and shoot:root ratio (W/W). Also, the P and Ca uptake efficiencies of this cultivar (160 and 75 µg/m respectively), and the dry matter yield (0.94 g) were among the highest. The total length of roots of Hl13–4 was a linear function of plant age (R² = 0.94) up to 30 days of age. Phosphorus and K uptake rates in solution culture decreased tremendously from 34 µgP/m-day and 380 µgK/m-day, at 5 days old, to 8 µgP/m-day and 95 µgK/m-day at 30 days, respectively. Deficiency of K in the solution culture markedly reduced P uptake by the root. It is concluded that Hl13x2013;4 variety has superior potential over other cowpea varieties studied for efficient utilization of applied P and K; and that the nutrient absorption capacity of young cowpea roots decreases rapidly with age.

Key Words: Root length • Shoot:root ratio • Root diametre • Roof surface area • P uptake rate • K uptake rate

² Lecturer and student, respectively, in Soil Science Dep., Univ. of Ife, Nigeria.

Received for publication August 16, 1976.