Forage production and plant density of irrigated alfalfa comparing different seeding densities

Abstract

Alfalfa is the most important forage species in the Colorado River Valley of Buenos Aires Province. However, there are no local data on the correct seeding density (sdn. den.) to obtain high forage production and persistence of the crop. A trial to compare plant density and forage production of irrigated alfalfa sown with different sdn. den. was conducted for 5 years on an entic Haplustol soil. Treatments were 286 (d1), 571 (d2), 857 (d3), and 1 143 (d4) viable seedsm-2 (dormancy category group 7) sown in rows with 0.15 m spacing. Total, leaf and stem forage production (kg DM ha-1 año-1) and plant density (number m-2) were estimated in a randomized complete block design with repeated measurements in time. The data were subjected to ANOVA, simple linear regression, slope equality test and Tukey’s multiple range test (P=0.05). Highest productions of total forage (18 021), leaf (10 366) and stem (7 655) were registered between the 2nd and 4th years. Total forage production was lower (by 1 364) at d1 than at the other sdn. den. Stem production did not differ between sdn. den. Leaf production was higher at d4 than d1. Seeding efficiency (live seedlings/live seeds) was 77% at d1 and 42% at d4. Plant number decreased progressively year by year at all sdn. den. Live plant number tended to be higher with increasing sdn. den. in all seasons. Simple linear regressions of live plant number (y) on days since seeding (x) were significant at all four sdb, den, b values being –0.11 a (d1), -0.16b (d2), -0.17bc (d3), and -0.20c (d4). Plant density threshold, below which forage production would be affected, was reached the 5th year at d2, d3 and d4 and the 4th year at d1. sdn. den higher than d2 involve an unnecessary additional cost of seed.