Hugo O. Chidichimo

Spatial pattern effect on corn (Zea mays) weeds competition in the humid Pampas of Argentina

Abstract The objectives of this study were to determine the effect of spatial pattern on corn above- and below-ground biomass, grain yield, weed above-ground biomass and soil water and photosynthetically active radiation (PAR) dynamics. Field studies were conducted in 2003 and 2004. Three corn hybrids with two spatial pattern (square and rectangular) under weed-free and weedy conditions were tested. Corn grain yield was greater in the square than in the rectangular pattern. This increase was related to better resources use while reducing the competition from weeds. Early in the growing season, there was greater moisture content in the intrarow at square pattern while a lower soil water content was observed at maturity. Conversely, the square pattern registered lower soil water content during the whole corn growing season in the interrow. This soil water profile was an outcome of the uniform corn below-ground biomass distribution. A greater PAR interception with a lower weed above-ground dry matter was obtained in square plant arrangement. The use of uniform spatial pattern appeared as an interesting alternative to increase both the grain yield potential and the corn suppressive ability against weeds in dry-land Argentinean production systems.

Traits Related to Competitive Ability of Wheat (Triticum aestivum) Varieties against Italian Ryegrass (Lolium multiflorum)

ABSTRACT The objective of this study was to determine which specific morphological characters are related with competitive ability and to establish their potential to suppress Lolium multiflorum growth while maintaining wheat grain yields. Field experiments were conducted at the La Plata National University Experimental Station (34°S 58°W), La Plata (Argentina) during 1997 and 1998. Wheat varieties used were Buck Charrúa, Klein Cacique and Pro Inta Super. A local ecotype of L. multiflorum was used. 280 plants m−2 of wheat and 50, 100 and 150 plants m−2 of Italian ryegrass were tested. The aggressivity index for aboveground dry matter and grain yield were used as a measure of competitive ability. A higher aggressivity of wheat varieties at first node, detectable up to 100 plants m−2 of weed was observed. For the 150 plants m−2 of weed, L. multiflorum had higher aggressivity than wheat varieties. At crop anthesis, weed aggressivity was higher than wheat varieties for the evaluated densities. No differences between varieties at 50 and 100 plant m−2 of L. multiflorum were observed. At first node detectable, aboveground dry matter and height of last expanded leaf of wheat, and photosynthetically active radiation interception were related with aggressivity. At anthesis, flag leaf length, flag leaf area, penultimate expanded leaf length and relative crop grain yield were positively correlated with aggressivity. This study demonstrates that variety differences in competitive ability of Argentinean wheat genotypes are significant at early crop stages up to 100 plants m−2 of L. multiflorum. Conversely there are no characters associated with wheat aggressivity at anthesis (for aboveground dry matter) and for grain yield.

Effects of Inoculation with Glomus mosseae in Conventionally Tilled and Nontilled Soils with Different Levels of Nitrogen Fertilization on Wheat Growth, Arbuscular Mycorrhizal Colonization, and Nitrogen Nutrition

Evaluation of the performance of inoculants in undisturbed and unsterilized soils, where diverse communities of microorganisms are present, is a necessary step before using arbuscular mycorrhizal fungi (AMF) in agricultural technology. The effects of inoculation with Glomus mosseae on arbuscular mycorrhizal colonization, growth, and nitrogen (N) uptake of wheat plants in unsterilized tilled and untilled soils from the Argentinean Pampas with different levels of N fertilization were assessed. The fertilization and inoculation effects depended on the tillage treatments. In no-tillage, the colonization was greater than in conventional tillage, but it was reduced by the N fertilization. In conventional tillage, the inoculation with G. mosseae increased colonization. Both conventional tillage and N fertilization promoted wheat root growth. Inoculation did not affect root growth but enhanced N concentration in roots when fertilizer was not applied.

Genotype-environment interaction in avena sativa l: employing AMMI and factorial correspondence models

The objective of this study was (i) to determine the presence of genotype-environment interaction (GXE) in Avena sativa L. for above dry matter yield of Schizaphis graminun tolerant and non-tolerant genotypes according to two different models: additive main effects and multiplicative interaction (AMMI) and factorial correspondence analysis; and (ii) to study and compare the results obtained with these models. Twelve genotypes and 12 environments were conducted at La Dulce and La Plata (Argentina) during three years (1993, 1994 and 1995). The environment (E), genotype (G) and GxE factors explained a 41.15%, 7.88% and 36.36% of the total sum of square, respectively. The first three axes of principal component analysis of AMMI were highly significant (p<0.001), explaining a 57.99%, 29.03% and 6.27% of interaction sum of square. The first three factorial correspondence coordinates accounted for 58.98%, 29.58% and 5.60% of the interaction sum of square. The relation- ships between tolerant genotypes-first clipping environments and non-tolerant genotypes-second clipping environments were reflected in the biplots of both models. The simultaneous use of AMMI and factorial correspondence analysis appeared as a useful methodology for the study of GxE interaction in the oat breeding for tolerance to Schizaphis graminum.

Acumulación, removilización, absorción postantesis y eficiencia de utilización de nitrógeno en trigo bajo diferentes labranzas y fertilizaciones

-1 de N como urea a la siembra, aplicacion de 90 kg ha -1 de N como nitrato de amonio calcareo a la siembra y aplicacion de N como urea y como nitrato de amonio calcareo en dosis de 45 kg ha -1 a la siembra mas 45 kg ha -1 a fin de macollaje, respectivamente. Se encontraron diferencias en el N acumulado entre sistemas de labranzas; con cincel se acumulo 18 kg ha -1

Shoot and root competition in a Lolium multiflorum-wheat association

ABSTRACT Three outdoor pot experiments with three wheat cultivars and Lolium multiflorum were conducted at La Plata National University (Argentina), where the effects of shoot and root competition were separated using aerial partitions. Root competition (RC) for both shoot dry matter yield (SDM) and grain yield was higher (p < 0.05) than shoot competition (SC). Cv. P.I. Super was most affected by SC while cvs. K. Cacique and B. Charrua were least affected. Crop competition caused a highly significant reduction of weed variables. RC had a greater effect on both weed SDM and weed seed yield than did SC. Cvs. B. Charrua and K. Cacique registered a higher photosynthetically active radiation interception (PAR) than cv. P.I. Super and L. multiflorum in SC treatment, but cv. P.I. Super intercepted more PAR than L. multiflorum and cvs. B. Charrua and K. Cacique in RC treatment. The resources complementarity for grain yield was obtained by means of relative yield total (RYT). There was resources complementarity when wheat and weed were in SC, but not in RC and full competition (FC), showing that the species were in full competition, despite the high nitrogen availability throughout the crop growing cycle. Cvs. B. Charrua and K. Cacique were more aggressive than the weed, while cv. P.I. Super was less aggressive than the weed in the SC treatment. Conversely, in both the RC and FC treatments, higher aggressivity than wheat cvs. was shown by the weed. This result could be ascribed to the lower shoot/root ratio and the higher nitrogen uptake of L. multiflorum. Despite the high availability of nitrogen, the results demonstrate that competition was mainly for soil nutrients, and wheat cvs. with a higher competitive ability in above-ground competition may have no competitive advantage when RC occurs. Because the experimental technique in pots does not reflect field conditions, caution is needed in extrapolating the results to a field situation.