Sa. Hossain et al., COMPARISON OF LEGUME-BASED CROPPING SYSTEMS AT WARRA, QUEENSLAND .2. MINERAL NITROGEN ACCUMULATION AND AVAILABILITY TO THE SUBSEQUENT WHEATCROP, Australian Journal of Soil Research, 34(2), 1996, pp. 289-297
Mineral nitrogen release following legume-based cropping systems for r
estoring the fertility of a Vertisol and the yield response and N upta
ke of subsequent wheat crops was studied. Legume phases of pastures, i
ncluding a 4 year grass+legume ley, and lucerne and medic leys (simila
r to 1 year) were terminated in October 1988 or 1989 and rotated with
wheat. Chickpea-wheat rotations matched those of lucerne and medic ley
s. Mineral N accumulations during a subsequent fallow period were dete
rmined by core sampling to 1 . 5 m in October, February and May. Grain
yield and N uptake of wheat enabled comparisons of the fertility rest
orative effects of the various systems relative to continuous wheat cr
opping. Averaged for two fallow periods, increases in mineral N down t
o 1 . 2 m depth were 93, 91, 68, and 37 kg/ha following grass+legume,
lucerne and medic leys, and chickpea, respectively, compared with the
continuous wheat treatment. Wheat yields were generally lower in 1989
(1 . 85-2 . 88 t/ha) than in 1990 (2 . 08-3 . 59 t/ha) following all l
eys and crops due to seasonal conditions. There was a grain yield incr
ease of 0 . 11 and 0 . 52 t/ha in 1989 and 1 . 23 and 1 . 26 t/ha in 1
990 following lucerne and medic leys, respectively and 0 . 85 t/ha in
1990 following a 4 year grass+legume ley. Following chickpea there was
a yield increase of 0 . 81 and 1 . 36 t/ha in 1989 and 1990 respectiv
ely. Nitrogen uptake by wheat was increased by 40 and 49 kg/ha in 1989
and 48 and 58 kg/ha in 1990 following lucerne and medic leys respecti
vely and 63 kg/ha in 1990 following a 4 year grass+legume ley. Followi
ng chickpea N uptake by wheat was increased by 27 and 32 kg/ha in 1989
and 1990 respectively. Grain protein concentration of wheat was subst
antially higher following all pasture leys (11 . 7-15 . 8%) than follo
wing wheat (8 . 0-9 . 4%) or chickpea (9 . 4-10 . 1%). Therefore, ther
e was substantial evidence of the effectiveness of pasture leys in soi
l fertility restoration, as reflected in mineral N, yield response and
N uptake by subsequent wheat crops.