H. Hafner et al., EFFECT OF CROP RESIDUES ON ROOT-GROWTH AND PHOSPHORUS ACQUISITION OF PEARL-MILLET IN AN ACID SANDY SOIL IN NIGER, Plant and soil, 150(1), 1993, pp. 117-127
The effect of long-term (1983-1988) applications of crop residues (mil
let straw, 2-4 t ha-1 yr-1) and/or mineral fertilizer (30 kg N, 13 kg
P and 25 kg K ha-1 yr-1) on uptake of phosphorus (P) and other nutrien
ts, root growth and mycorrhizal colonization of pearl millet (Penniset
um glaucum L.) was examined for two seasons (1987 and 1988) on an acid
sandy soil in Niger. Treatments of the long-term field experiment wer
e: control (-CR-F), mineral fertilizer only (-CR+F), crop residues onl
y (+CR-F), and crop residues plus mineral fertilizer (+CR+F). In both
years, total P uptake was similar for +CR-F and -CR+F treatments (1.6-
3.5 kg P ha-1), although available soil P concentration (Bray I P) was
considerably lower in +CR-F (3.2 mg P kg-1 soil) than in -CR+F (7.4)
soil. In the treatments with mineral fertilizers (-CR+F; +CR+F), crop
residues increased available soil P concentrations (Bray I P) from 7.4
to 8.9 mg kg-1 soil, while total P uptake increased from 3.6 to 10.6
kg P ha-1. In 1987 (with 450 mm of rainfall), leaf P concentrations of
30-day-old millet plants were in the deficiency range, but highest in
the +CR+F treatment. In 1988 (699 mm), leaf P concentrations were dis
tinctly higher, and again highest in the +CR+F treatment. In the treat
ments without crop residues (-CR-F; -CR+F), potassium (K) concentratio
ns in the leaves indicated K deficiency, while application of crop res
idues (+CR-F; +CR+F) substantially raised leaf K concentrations and to
tal K uptake. Leaf concentrations of calcium (Ca) and magnesium (Mg) w
ere hardly affected by the different treatments. In the topsoil (0-30
cm), root length density of millet plants was greater for +CR+F (6.5 c
m cm-3) than for +CR-F (4.5 cm cm-3) and -CR+F (4.2 cm cm-3) treatment
s. Below 30 cm soil depth, root length density of all treatments decli
ned rapidly from about 0.6 cm cm-3 (30-60 cm soil depth) to 0.2 cm cm-
3 (120-180 cm soil depth). During the period of high uptake rates of P
(42-80 DAP), root colonization with vesicular-arbuscular mycorrhizal
(VAM) fungi was low in 1987 (15-20%), but distinctly higher in 1988 (5
5-60%). Higher P uptake of +CR+F plants was related to a greater total
root length in 0-30 cm and also to a higher P uptake rate per unit ro
ot length (P influx). Beneficial effects of crop residues on P uptake
were primarily attributed to higher P mobility in the soil due to decr
eased concentrations of exchangeable Al, and enhancement of root growt
h. In contrast, the beneficial effect of crop residues on K uptake was
caused by direct K supply with the millet straw.