R.W. Benjamin
Agricultural Research Organization, Israel
2.3 Growth characteristics and primary production
2.4 Chemical properties and digestibility
The Norte Chico is a semi-arid region with a mean annual winter rainfall ranging from 100 mm in the north to 220 mm in the south. Drought due to low total rainfall and bad rainfall distribution is a common occurrence. These conditions preclude the growing of profitable cash crops in the region because of frequent crop failures and dangers of serious soil erosion of the 20–25 cm sandy-loam soil overlaying a hard clay subsoil. Farming is therefore limited to the grazing animal, but here too, profitability is marginal per unit area and only large landholders can command reasonable incomes. Small landholders, the majority of the people, can only earn small incomes and must find alternative sources of income. In the absence of outside work they try to provide their main food diet, bread, from cultivating wheat wherever possible with disastrous consequences to themselves and the natural vegetation. Today as the result of cultivation, native shrubs, once a common feature of the landscape, are conspicuous by their absence.
Of great concern has been the overall reduction in stock numbers and changes in the animal composition of the region that has caused a lowering of per capita income from pastoral farming during the last 15 years. Animal census figures are presented in Table 1 to illustrate these changes. Table 2 presents the annual rainfall from 1944 to 1979.
Table 1. Stock numbers and the changes relative to 1955, from 1955–1975 in the combarla and nincha districts of the norte chico (numbers are 1x103).
1955 |
1965 |
1975 | ||||
No |
% |
No |
% |
No |
% | |
Goats |
123 |
100 |
84 |
68 |
114 |
93 |
Sheep |
72 |
100 |
43 |
60 |
35 |
49 |
Cattle |
10 |
100 |
6 |
60 |
5 |
50 |
Total |
205 |
100 |
133 |
69 |
150 |
75 |
Table 2. Annual rainfall in mm and expressed as proportion of the mean rainfall, together with a classification of the rainfall year.
Year |
mm |
Proportion of mean |
Classificationa |
Year |
mm |
Proportion of mean |
Classification |
1944 |
397.1 |
1.814 |
e |
1963 |
376.7 |
1.721 |
e |
1945 |
163.8 |
0.748 |
b |
1964 |
96 |
0.438 |
b |
1946 |
174 |
0.794 |
c |
1965 |
472.6 |
2.159 |
e |
1947 |
199.7 |
0.912 |
c |
1966 |
285.7 |
1.305 |
d |
1948 |
237.9 |
1.086 |
c |
1967 |
165.4 |
0.755 |
b |
1949 |
235.2 |
1.047 |
c |
1968 |
55.2 |
0.252 |
a |
1950 |
229.7 |
1.049 |
c |
1969 |
69.9 |
0.442 |
b |
1951 |
221.8 |
1.013 |
c |
1970 |
230.3 |
1.052 |
c |
1952 |
279.8 |
1.278 |
d |
1971 |
205.1 |
0.937 |
c |
1953 |
340.6 |
1.556 |
c |
1972 |
320.9 |
1.466 |
d |
1954 |
250 |
1.142 |
c |
1973 |
208.7 |
0.953 |
c |
1955 |
136 |
0.621 |
b |
1974 |
167.8 |
0.766 |
c |
1956 |
217 |
0.991 |
c |
1975 |
97.3 |
0.444 |
b |
1957 |
441 |
2.014 |
c |
1976 |
145.2 |
0.663 |
b |
1958 |
226 |
1.032 |
c |
1977 |
254.5 |
1.162 |
d |
1959 |
167 |
0.763 |
b |
1978 |
272.4 |
1.244 |
d |
1960 |
113 |
0.516 |
b |
1979 |
78.8 |
0.351 |
a |
1961 |
211 |
0.964 |
c |
||||
1962 |
111 |
0.507 |
b |
Median: 209.5 Mean: 218.869 S.D.: ± 96.68
a very dry b: dry :c average d: wet e: very wet.
The large reduction in stock numbers was the direct result of a severe three-year drought period between 1959 and 1962. There was another severe drought in 1968 and 1969 when there were only up to 70 mm of rainfall per annum. The fear of drought and falling incomes appears to have led to the increase in goat numbers relative to other livestock especially in the inventories of small land holders. This seems to be due to the greater survival ability of the goat to drought conditions and the greater suitability of the goat to provide a subsistence level of living to the farmer in the form of milk and meat.
Large areas of the higher-rainfall southern part of the Norte Chico had, and in some localities still have, large populations of native shrubs. Most of these shrubs are unpalatable to livestock. However because of their resistance to drought and their ability to retain green leaves during dry periods, it was thought that the introduction of palatable forage shrubs could answer problems of forage availability both within and between years and, in addition, to replace the native shrubs that had disappeared due to cultivation practices. To investigate the feasibility of introducing forage shrubs into the region and to determine their possible value within grazing systems a series of studies were initiated at Los Vilos experimental station in 1971 to answer the following questions:
From the results of previous experiments elsewhere in Chile the following species were selected for intensive study: Atriplex repanda, Atriplex nummularia, Atriplex semibaccata, Galenia secunda, Kochia brevifolia.
Large-scale propagation in the Norte Chico region, implied the need for large amounts of seed and/or vegetative techniques for the production of seedlings. All the species were found to have good seed production capabilities, however germination properties varied considerably between species. Table 3 presents the results of a germination study.
The species in Table 3 have been ranked in order of % age germination in the control and after immersion in water for up to 48 hours. Because this experiment was made in vitro the germination recorded is not that which would be obtained in the field but is reflective of the relative performance of each species.
Table 3. The in vitro germination of seeds of various fodder bushes under different treatments. 26.7.75 (% germination)
Species |
Days to Germinate |
Control |
24-48h in H20 |
H2S04 |
HN03 |
Immersion for 2-60 minute | ||
HC1 |
NaOH |
KOH | ||||||
G.secunda |
11 |
80 |
94 |
100 |
100 |
96 |
96 |
100 |
K. brevifolia |
9 |
60 |
82 |
88 |
76 |
80 |
80 |
100 |
A. nummularfa |
20 |
30 |
52 |
60 |
70 |
64 |
40 |
58 |
A. semibaccata |
20 |
28 |
34 |
42 |
82 |
32 |
34 |
30 |
1A. repanda |
44 |
14 |
10 |
24 |
20 |
14 |
22 |
30 |
1Native to Chile
Sowing in the field after discing at the rate of up 1 kg of untreated seed per hectare produced satisfactory germination and establishment at many sites for G. secunda, A. semibaccata (Kartzow and Laihacar, 1965) and K. brevifolia (Gasto and Contreras 1972). The results for A. repanda were successful at one site but unsuccessful at others.
Because of the poor germination results recorded for A. repanda and A. nummularia and elsewhere in Chile (Lailhacar and Laude, 1975), these two species are propagated in the nursery by planting young branches in pots (Pena, 1978) and the resulting seedlings are planted out in contour furrows.
From observational studies at Los Vilos and elsewhere in the Norte Chico A. semibaccata, K. brevifolia and G. secunda appeared to volunteer profusely.
The bulk of the annual dry matter production is produced in the spring and summer months. At other times of the year the shrubs appear to be almost dormant (Gasto and Contretras, 1972).
Annual primary production is limited by both within year rainfall and the previous years' rainfall. It is further severely limited by nutrient deficiencies of nitrogen and phosphorus. In the absence of fertilizer application annual edible dry matter yields higher than 2000 kg per hectare cannot be attained.
Coyne and Cook (1970) in the USA found that desert perennials show a depletion of total available carbohydrates in storage organs in spring when new growth occurs. They show replenishment of reserves during later stages of growth and reach maximum reserve storage at seed maturity. This corresponds to the time when shrubs are also making root growth and edible shoot production; further because of the root and shoot growth this is also the time when the nutrient value of the shrubs is at its highest.
The edible components of the shrubs show a relatively constant crude protein, fibre and ash content of up to 20%, 17% and 30% respectively. In general the shrubs have a similar crude protein content to annual vegetation in the spring but a consistent and significant higher content at all other times of the year (Contreras, 1977). On the basis of crude protein content, forage shrubs can be theoretically considered as a supplement to protein deficient pastures. Wilson (1966) in Australia when feeding Atriplex leaves to penned sheep as a protein supplement to roughages, recorded some positive response. However no comparable work can be cited in which responses were recorded when forage shrubs supplemented the diets of grazing animals in experiments with adequate non-supplemented controls or in which another protein source was used as a control1.
Digestibilities for edible components such as leaves and growing tips, of up to 70% have been recorded in the spring and as low as 40% in the autumn and winter. A factor in the poor expression of the high crude protein content in terms of animal performance has been reported by Weston et al. (1970). There appears to be ruminal degradation of aminoacids to ammonia which escapes absorption in the rumen. The absorption of remaining nitrogenous compounds appears to take place at lower sites in the intestines than is usual for other plant proteins. In this way available digestible protein may be reduced by up to 40%.
In general the palatability of most of the shrubs is low when green annual species are available. A. repanda seemed to be an exception as are the young seedlings of both A. repanda and A. nummularia. All shrubs become more acceptable when annual species are either mature and dry or of low availability.
No reliable figures are available for daily intakes under grazing conditions in Chile and little information is available from elsewhere.(1)
________________________________________
(1)Editor's note. The statements are in contradiction with the paper by Dumancic and Le Houérou in these Proceedings, and also with Franclet et Le Houérou, 1971; Sarson, Tchamitchian and Novikoff, 1921; Granier, 1976, etc.
When hand fed as sole diets to sheep in Australia Wilson (1960) recorded 1.5 kg/day for A. vesicaria and 0.8 kg for A. nummularia. Eyal and Benjamin (1958) reported up to 0.5 kg for A. halimus in Israel. Under grazing conditions, the diet selected in both quantity and quality may be quite different from that recorded for hand fed sheep. Furthermore the diet of grazing sheep is rarely 100% from forage bushes.
Intake from forage bushes is substantially influenced by sparse stands of palatable species in the pasture. This results in animals spending more time in search of preferred plants and parts of plants (Cook, 1973). Leigh and Mulham (1966) reported that when A. vesicaria was 75% of the forage available at initiation of grazing it was only 1% of the diet selected.
The high sodium content found in the ash of the species examined increases the water requirement of animals grazing forage bushes. Wilson (1974), reported that sheep grazing A. vesicaria in Australia drank 7–12 litres of water per day whereas sheep grazing drank only 3–4 litres. Intakes from forage bush dominated pastures may be limited by the availability of drinking matter needed for the excretion of high salt intakes.
Most of the introduced shrubs were evolved in the absence of continuous grazing pressures. The absence of spines, the relatively free access of grazing animals to remove primordia and the inability of some bushes to produce viable lateral or epicormic buds makes these species vulnerable to destruction through grazing (Osborn et al, 1932). With some of them low palatability offsets low resistance to grazing. However low palatability is of no consequence when alternative feed sources are absent.
With annual species, the ability to survive grazing, in the sense that they can maintain their proportion in the plant composition of the pasture, depends on their ability to produce an amount of seed that would appear necessary to produce a relatively constant number of seedlings annually (Loria, 1980). With perennial shrubs, survival appears dependent on maintaining or replenishing carbohydrate reserves and adequate root growth during the growing season (Crider, 1955, 1955; Cook, 1966).
Heavy grazing during the spring and summer period of rapid shrub growth causes severe reductions in carbohydrate reserves and root growth. So that most shrubs are severely stunted and even killed following severe defoliation especially under conditions of drought. Cider (1955) reported that root growth can be maintained if less than 40% of the leaves are removed.
On the other hand heavy grazing resulting in severe defoliation in the autumn and winter followed by non-grazing conditions in the spring and summer does not appear to adversely affect the shrubs. Trivelli, 1973).
In Chile the introduction of bushes on a large scale is carried out by the forestry service. Atruplex repanda and 4tliplex nummularia are the principal species planted as they can be considered by the forestry department as a reasonable alternative to tree plantations. G. secunda and Atriplex semihaccata because of their low growth habit are not considered as alternatives to trees. In order to prevent grazing during the two years following establishment and subsequent grazing in the spring and summer all shrub plantations must be permanently fenced. The cost of contour furrowing, seedling establishment and fencing is 200 $ US. per hectare.
Thus as the result of the use of A. repanda and A. nummularia grazing management consists of a two paddock system: spring-summer grazing of annual vegetation pastures; autumn-winter grazing of forage shrub pastures.
The experimental designs used for the grazing at Los Vilos and elsewhere in the Norte Chico did not allow an evaluation of the performance of sheep in response to the grazing of pastures in which forage bushes had been introduced.
In the absence of severe drought during the years of study, particularly the absence of two or more years of continuous drought it was impossible to study the value of forage bushes as the principal diet of breeding sheep. The two paddock systems studied meant that in all years there was high availability of dry annual species in addition to the forage bushes. Under these conditions it was impossible to show that there was a protein deficiency in the diet selected by the sheep from the annual species present. In addition there was never any possible energy deficiency.
As lambs were born and grew to weaning under conditions of the grazing of annuals, no increases in weaned lamb weight could possibly be attributed to forage bushes. Furthermore the mating of ewes in December-January at the time of initiation of grazing of forage bush pastures, precluded attributing possible fertility improvements directly to forage bushes. In some instances increased lamb birthweights were recorded, but in these cases evidence was not conclusive as there was no adequate two paddock annual pasture control available.
In no experiment was it possible to show any possible economic return per unit land area that could pay for the overhead expenses of establishing and maintaining forage bush areas.
The evidence from the work at Los Vilos indicates that the principal contribution of forage bushes should be to increase feed availability per unit land area where dry periods and drought years are common occurrences. In particular it would appear that the vital need for forage bush availability would be in the second and third years of a continuous drought when no other grazing forage may be available. However all indications are that grazing bushes under such conditions in the spring and summer would kill them. The alternative not to graze the bushes would entail high animal losses. As little information is available on the long term effects of the continuous grazing of forage bushes on animals there is a possibility of animal losses due to such factors as oxalate poisoning, in which case continuous grazing of forage bushes in drought years could mean the loss of both animals and bushes.
The choice of A. repanda and A. nummularia for extensive introduction into pasture areas may have been unfortunate. The use of A. semibaccata and G. secunda on the other hand would have entailed a lower per unit area establishment cost as they can be sown into the pasture and their volunteering characteristics enable them to spread rapidly especially under grazing conditions. Their survival as a component in a pasture appears more dependent, as with annuals, on the production of viable seed and not on individual plant survival. Thus they can be grazed as if they were annual components of the pastures eliminating the cost of the extra fencing needed for a two paddock rotational grazing system.
Their low palatability relative to the annual species ensures that other things being equal they will be available at times of low availability of preferred species in the late summer and in drought years.
In the absence of solid evidence in Chile of demonstratable economic benefits accruing to the grazing of forage bushes it is difficult to justify high per unit area costs involved in establishing and maintaining such bushes as A. repanda and A. nummularia.
This article is a summary of a report written by the authors "Forage shrub research at Los Vilos ". Report No. 2 of the results of the UNDP/BID Regional Project Chile. Rehovot, Israel.
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