13. Production and water use of several food and fodder crops under irrigation in the desert area of southwestern Peru.
Agricult. Res. Rep. 928, Pudoc, Wageningen; ISBN 90-220 0869X, 1984, vi + 50 p.
This report describes the results of a research project in the desert of southwestern Peru that was carried out jointly by researchers from Peru, Israel and the Netherlands.
The main purpose of the project was to investigate dry matter production and water use of the most important crops in the region under irrigated conditions and fertilizer application. To facilitate the necessary measurements and analyses, an existing laboratory was improved and measuring instruments were purchased.
In addition to field trials, pot trials were carried out, mainly to determine the transpiration coefficient (TRC), i.e. the amount of water transpired per unit of dry matter produced.
The crops mainly studied were alfalfa, maize and potatoes, which are the most important crops in the region, and Rhodes grass for comparison. All crops were sprinkler irrigated, but in a few cases trickle irrigation was used for comparison. By periodic harvesting - usually at weekly intervals - data for growth curves, the time course of the leaf area index, light interception and dry matter partitioning were compiled. In addition, the water supply to the crop was measured as well as the soil water content before and after watering. The results obtained were compared with those obtained elsewhere, sometimes also with simulation programs.
The rate of growth of an alfalfa sward varied with the season; it was higher in summer than in winter. A ceiling yield was reached earlier in the year and was more pronounced than at the end of the year. The local variety Tambo gave higher yields than the Californian variety Moapa, mainly due to higher ceiling values. Under the prevailing conditions, fertilization with P and K was not necessary; N fertilization resulted in slightly higher yields, but without fertilization an amount of N of about 700 kg per ha per year was fixed by Rhizobia bacteria. No clear relation could be demonstrated between the rate of regrowth and the amount of reserve carbohydrates left in the remaining plant parts after cutting. There was a relation between regrowth in the light and in the dark, indicating that, in some way, carbohydrate reserves are important.
Maize in the project area had a slower initial growth under optimal conditions than elsewhere in the world, but in the linear phase growth rates were comparable to those in other arid zones, leading to yields of around 25 tonnes of harvestable dry matter per ha.
Rhodes grass formed such a very dense sward that weeds were not able to penetrate. During the summer months, yields were high enough to be able to compete with other foddercrops, but during winter, growth virtually stopped, mainly due to the low night temperatures. For this reason, large scale use of Rhodes grass is not recommended on the desert plains of Peru.
Potatoes, well supplied with water and nutrients, yielded around 70 tonnes of fresh tubers per hectare - comparable to yield levels elsewhere in the world. Again the Peruvian variety yielded more than a Dutch variety, but as the latter had a more homogeneous tuber size, the marketable yield was about the same.
The relationship between the amount of dry matter produced and water received at increasing distances from a single sprinkler irrigation line was established by measurement.
For potatoes this relation was linear, almost up to the highest amount of water applied.
For alfalfa a comparable relation was found. When more than 250 mm water was applied, the crop did not show a response; below this value the relation was linear, down to about 50 mm water.
Both with alfalfa and with maize, experiments were carried out in which the amount of water applied to different plots was varied in relation to the evaporation of a Class A pan. For alfalfa, this resulted again in a rectilinear relation between dry matter production and water application up to about 250 mm water applied for both varieties and in all seasons.
Application of an artificial mulch gave a better utilization of the irrigation water.
The relation between dry matter production and the amount of water evapo-transpired could be calculated from the soil water measurements.
For maize, the results were less conclusive, partly because the trial was carried out in the unfavourable season.
The highest yield was attained when water was applied at a high and constant rate for the lower plant density. Trickle irrigation instead of using sprinklers saved a considerable amount of water, however, due to the higher costs, a trickle irrigation can only be profitable if it can also be used for other crops.
Some different soil types of the pampa were tested on their water holding capacity in a lysimeter experiment with alfalfa as the test crop. When well watered and fertilized, all soils were able to give good yields. However, some soils needed to be irrigated every other day, which would require too much labour in normal practice to use them economically.
The value of the results for farming in the regions is discussed.
Author's summary, shortened.
1236 92 - 11/57
Latin America, Dominican Republic, study, on-farm project, evaluation methods, agriculture, land-tenure, land-labour relationship, irrigation systems, irrigation organization, finances, institutions, DESFIL
HANRAHAN, M. et al.
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