Many Australian cotton growers now include legumes in their cropping system. Three experiments were conducted between
1994 and 1997 to evaluate the rotational effects of winter or summer legume crops grown either for grain or green manuring
on following cotton (Gossypium hirsutum L.). Non-legume rotation crops, wheat (Triticum aestivum) and cotton, were
included for comparison. Net nitrogen (N) balances, which included estimates of N associated with the nodulated roots, were
calculated for the legume phase of each cropping sequence. Faba bean (Vicia faba Ð winter) ®xed 135±244 kg N ha
ÿ1 and
soybean (Glycine max Ð summer) ®xed 453±488 kg N ha
ÿ1 and contributed up to 155 and 280 kg ®xed N ha
ÿ1, respectively,
to the soil after seed harvest. Green-manured ®eld pea (Pisum sativum Ð winter) and lablab (Lablab purpureus Ð summer)
®xed 123±209 and 181±240 kg N ha
ÿ1, respectively, before the crops were slashed and incorporated into the topsoil.
In a separate experiment, the loss of N from 15N-labelled legume residues during the fallow between legume cropping and
cotton sowing (5±6 months following summer crops and 9 months after winter crops) was between 9 and 40% of 15N added; in
comparison, the loss of 15N fertilizer (urea) applied to the non-legume plots averaged 85% of 15N added. Little legume-derived
15N was lost from the system during the growth of the subsequent cotton crop.
The improved N fertility of the legume-based systems was demonstrated by enhanced N uptake and lint yield of cotton. The
economic optimum N fertilizer application rate was determined from the ®tted N response curve observed following the
application of N fertilizer at rates between 0 and 200 kg N ha
ÿ1 (as anhydrous ammonia). Averaged over the three
experiments, cotton following non-legume rotation crops required the application of 179 kg N ha
ÿ1, whilst following the
grain- and green-manured legume systems required only 90 and 52 kg N ha
ÿ1, respectively.
In addition to improvements in N availability, soil strength was generally lower following most legume crops than nonlegume
rotation crops. Penetrometer resistance during the growth of the subsequent cotton crop increased in the order faba
bean, lablab, ®eld pea, wheat, cotton, and soybean. It is speculated that reduced soil strength contributed to improvement in
lint yields of the following cotton crops by facilitating the development of better root systems. # 2001 Elsevier Science B.V.
All rights reserved.
Many Australian cotton growers now include legumes in their cropping system. Three experiments were conducted between1994 and 1997 to evaluate the rotational effects of winter or summer legume crops grown either for grain or green manuringon following cotton (Gossypium hirsutum L.). Non-legume rotation crops, wheat (Triticum aestivum) and cotton, wereincluded for comparison. Net nitrogen (N) balances, which included estimates of N associated with the nodulated roots, werecalculated for the legume phase of each cropping sequence. Faba bean (Vicia faba Ð winter) ®xed 135±244 kg N haÿ1 andsoybean (Glycine max Ð summer) ®xed 453±488 kg N haÿ1 and contributed up to 155 and 280 kg ®xed N haÿ1, respectively,to the soil after seed harvest. Green-manured ®eld pea (Pisum sativum Ð winter) and lablab (Lablab purpureus Ð summer)®xed 123±209 and 181±240 kg N haÿ1, respectively, before the crops were slashed and incorporated into the topsoil.In a separate experiment, the loss of N from 15N-labelled legume residues during the fallow between legume cropping andcotton sowing (5±6 months following summer crops and 9 months after winter crops) was between 9 and 40% of 15N added; incomparison, the loss of 15N fertilizer (urea) applied to the non-legume plots averaged 85% of 15N added. Little legume-derived15N was lost from the system during the growth of the subsequent cotton crop.The improved N fertility of the legume-based systems was demonstrated by enhanced N uptake and lint yield of cotton. The
economic optimum N fertilizer application rate was determined from the ®tted N response curve observed following the
application of N fertilizer at rates between 0 and 200 kg N ha
ÿ1 (as anhydrous ammonia). Averaged over the three
experiments, cotton following non-legume rotation crops required the application of 179 kg N ha
ÿ1, whilst following the
grain- and green-manured legume systems required only 90 and 52 kg N ha
ÿ1, respectively.
In addition to improvements in N availability, soil strength was generally lower following most legume crops than nonlegume
rotation crops. Penetrometer resistance during the growth of the subsequent cotton crop increased in the order faba
bean, lablab, ®eld pea, wheat, cotton, and soybean. It is speculated that reduced soil strength contributed to improvement in
lint yields of the following cotton crops by facilitating the development of better root systems. # 2001 Elsevier Science B.V.
All rights reserved.
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