An experiment to determine the distribution of forage production of some Argentine alfalfa cultivars throughout the growing season is being conducted at Manfredi Exp. Stn.-INTA, Cordoba, Argentina. Five INTA’s cultivars [Victoria SP INTA (FD=6); Perla SP INTA (FD=6); Esmeralda SP INTA (FD=6); Monarca SP INTA (FD=8); and Barbara SP INTA (FD=8)] and an Egyptian experimental line (FD=10) were planted in the fall, 1998.

The varieties were planted in 12 m2 plots arranged in a complete randomized block design with three replicates. The methodology of sequence cutting described by Anslow & Green (1967) was used. Cutting sequences began in September 1998 and lasted until June 1999. At each harvesting time, three sequences —cutting at 10% blooming with 7-day intervals- were defined. Dry matter (DM) production and growth rates for each period were calculated based on DM yield of each cut. Analysis of variance was performed on annual and seasonal DM production, using Duncan test (?=0.05) to compare the means. Growth rates were preformed to polynomial function. During all growing season there was an important soil moisture stress with a total rainfall of 831 mm and an evapotranspiraition of 950 mm.

In this first growing season, there were no differences (p>0.05) in DM production among the six varieties, reaching a general mean of 7.4 Mg DM ha-1. This amount of forage is lesser than a normal yield for the area and it was related to the above mentioned moisture stress
 
 

Figure 1: Growth rate (kg DM ha-1 day —1)of alfalfa cultivars

There were no differences in the distribution of production along the season. The largest growth rates (>40 kg DM ha-1 day—1) were reached in December-January (summer) whereas the smallest ones (<15 kg DM ha-1 day —1) were produced in May (end of fall). For the rest of the season, growth rates were between 25 to 40 kg DM ha-1 day —1. Higher rainfall during March and April were not reflected in higher growth rates. Non-dormant materials (FD 8 — 10) were able to growth until beginning of winter.

The growth rate of alfalfa cultivars fitted a polynomial of 6th grade function like:

y = a x6 -b x5 + c x4 - d x3 +e x2 - f x g

Where: y = kg DM ha-1 day —1

X = days since 1st cut

Reference:

Anslow, R.C. and Green, J.O. (1967). The seasonal growth of pasture grasses. J.Agric.Sci.Camb.;68:109-122.

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