Influence of cover crops on nitrogen availability, soil moisture content and maize yield under sub humid climate of Morogoro, Tanzania
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Date
2005
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Publisher
Sokoine University of Agriculture
Abstract
A study was conducted in Morogoro Tanzania, for 3 consecutive years to evaluate the
influence of cover crops planted in short rains on nitrogen (N) availability, soil moisture
and grain yield of the subsequent maize crop planted in the long rains. The cover crops
namely cowpea (Vigna unguiculata [L] Walp.), lablab (Lablab purpureus, L.), mucuna
(Mucuna pniriens) and pumpkin (Cucurbita maxima') were evaluated against weed and
bare fallows in Randomized Complete Block Design (RCBD) replicated three times.
Cover crops residues had N content
2%. Pumpkin, although not a legume, had high
quality residues, having 2.1% N and higher P (0.25% P) and base content than other cover
crops. Mucuna was the only cover crop that produced an average biomass above the
threshold of 2 Mg DM ha'1. Mucuna biomass was significantly higher (P < 0.05) than that
of the other cover crops, ranging from 2.7 to 5.1 Mg DM ha'1, with good short rains and
accumulating 63 to 118 kg N ha'1. At the end of the short rainy season, mineral N after
mucuna increased by 2 to 30% and was significantly higher (P < 0.05) than after the other
cover crops. Seventeen and 35% of N accumulated in pumpkin and cowpea residues was
released in the first 7 days of incubation, respectively. These were significantly higher
than the 4 and 6% accumulated N in lablab and mucuna residues, respectively. At 35 days
of incubation, mineral N released from lablab, pumpkin and mucuna residues was 19, 34
and 31% of the applied amount, respectively. Mucuna and lablab significantly increased
soil moisture reserve in the 40 - 60 cm soil layer (P < 0.05) by 9 mm in the short rainy
season whereas pumpkin and weed fallow reduced it by 3 and 4 mm, respectively. In the
long rainy seasons, mucuna and lablab reduced runoff from 30 - 45% to 6 - 15% of
rainfall. Mucuna significantly increased the number of maize plant silking (P < 0.05) at 53
days after planting by 15 - 17% over weed fallow and maize grain yield by 3 - 4 fold in seasons with insufficient long rains. It is recommended that in order to increase maize
production in the sub humid area of Morogoro, mucuna should be planted in the short
rains instead of leaving the land under weed fallow and supplemental mineral N fertilizer
should be topdressed at 28 to 35 days after maize planting.
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Thesis
Keywords
Nitrogen availability, Soil moisture, Maize yield, Sub humid climate, Morogoro, Tanzania