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TRADE-OFFS BETWEEN BIOMASS USE AND SOIL COVER. THE CASE OF RICE-BASED CROPPING SYSTEMS IN THE LAKE ALAOTRA REGION OF MADAGASCAR
- K. NAUDIN, E. SCOPEL, A. L. H. ANDRIAMANDROSO, M. RAKOTOSOLOFO, N. R. S. ANDRIAMAROSOA RATSIMBAZAFY, J. N. RAKOTOZANDRINY, P. SALGADO, K. E. GILLER
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- Journal:
- Experimental Agriculture / Volume 48 / Issue 2 / April 2012
- Published online by Cambridge University Press:
- 20 October 2011, pp. 194-209
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Farmers in the Lake Alaotra region of Madagascar are currently evaluating a range of conservation agriculture (CA) cropping systems. Most of the expected agroecological functions of CA (weed control, erosion control and water retention) are related to the degree of soil cover. Under farmers’ conditions, the grain and biomass productivity of these systems is highly variable and the biomass is used for several purposes. In this study, we measured biomass production of cover crops and crops in farmers’ fields. Further, we derived relationships to predict the soil cover that can be generated for a particular quantity of mulch. We used these relationships to explore the variability of soil cover that can be generated in farmers’ fields, and to estimate how much of the biomass can be removed for use as livestock feed, while retaining sufficient soil cover. Three different kinds of cropping systems were investigated in 91 farmers’ fields. The first two cropping sequences were on the hillsides: (i) maize + pulse (Vigna unguiculata or Dolichos lablab) in year 1, followed by upland rice in year 2; (ii) the second crop sequence included several years of Stylosanthes guianensis followed by upland rice; (iii) the third crop sequence was in lowland paddy fields: Vicia villosa or D. lablab, which was followed by rice within the same year and repeated every year. The biomass available prior to rice sowing varied from 3.6 t ha−1 with S. guianensis to 7.3 t ha−1 with V. villosa. The relationship between the mulch quantity (M) and soil cover (C) was measured using digital imaging and was well described by the following equation: C = 1 − exp(−Am × M), where Am is an area-to-mass ratio with R2 > 0.99 in all cases. The calculated average soil cover varied from 56 to 97% for maize + V. unguiculata and V. villosa, respectively. In order to maintain 90% soil cover at rice sowing, the average amount of biomass of V. villosa that could be removed was at least 3 t ha−1 for three quarters of the fields. This quantity was less for other annual or biennial cropping systems. On average the V. villosa aboveground biomass contained 236 kg N ha−1. The study showed that for the conditions of farmers of Malagasy, the production and conservation of biomass is not always sufficient to fulfil all the above-cited agroecological functions of mulch. Inventory of the soil cover capacity for different types of mulch may help farmers to decide how much biomass they can remove from the field.
Selective grazing by dairy cows in the presence of dung and the defoliation of tall grass dung patches
- J. Bao, P. S. Giller, G. Stakelum
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- Journal:
- Animal Science / Volume 66 / Issue 1 / February 1998
- Published online by Cambridge University Press:
- 02 September 2010, pp. 65-73
- Print publication:
- February 1998
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Two studies investigated the effect of contaminated pasture on selective grazing, overall grazing behaviour and the process of defoliation of dung patches through experiments targeted at four major questions: (a) how does relative utilization of tall and short grass change as the sward is grazed down? (b) what effect does herbage mass and sward height have on the relative utilization of short and tall grass? (c) how are tall grass patches actually utilized by cattle? and (d) how is overall grazing behaviour influenced by contamination of the sward?
Experiments were conducted in mid to late season using Friesian dairy cattle. In experiment 1, two -pasture types (topped sward (T) v. grazed-only sward (G)) were used. The distribution of bites on tall grass from both pasture types indicated that the grazing animals tended initially to graze short grass when they met a new sward, and then select tall grass as the swards were progressively grazed down. This switch happened earlier in the defoliation process in the topped sward. In experiment 2 observations were conducted on previously grazed and previously ungrazed swards. The distribution of bites on tall grass showed a similar trend to that found in experiment 1 and as the sward was gradually grazed, biting rate significantly declined. There was also a significantly higher total grazing time on the previously ungrazed sward (no contamination by dung). Comparing data based on a consistent biting rate (calculated as the time for 20 consistent bites) and natural biting rate (calculated as the total time for 20 bites) suggested that the grazing animals had increased difficulty in handling tall grass which may explain the declining biting rate as the swards were being grazed down and more bites were directed at tall grass. The defoliation of tall grass dung patches appeared to be concentrated around the edges of the patch. The average area of sward affected by a single dung pat was 1·04 m2 measured at the pre-grazing stage and was markedly reduced to 0·51 m2 at the post-grazing stage. In conclusion, selective grazing is likely to exist due to the presence of dung and conditioned by dung distribution and sward type and this in turn modifies biting rate during grazing down of a sward.