Effects of Sowing Date, Climate and Genotype On Wheat Yield and Its Components.

Wheat is the most important crop in the semiarid temperate region of Argentina but there is a large variability in grain yield in the last decade varied from 1056 to 2594 kg ha^-1. The most important concern in semiarid areas is water availability and its efficient use. Rainfall in this region varies between 274 and 1166, annually and usually falls short of satisfying crop water requirements. Although wheat yield is related to seasonal rainfall, water efficiency can be substantially improved by crop management practices as well. The right choice of sowing date and cultivar are important management decisions to optimise grain yield in this environment. Several studies have been carried out to investigate the performance of different cultivars at three sowing dates in relation to years with different water availability. The study was conducted at the Experimental Farm of the Faculty of Agronomy of the Universidad Nacional de La Pampa (36°46’S 64°16’W) during 2006, 2007 and 2008 at three sowing dates: early (end of May), intermediate (end of June) and late (end of July). Within each sowing date 5 cultivars adapted to each sowing date were utilized. Grain yield in each year was different. The highest yield (3553 kg ha^-1) was obtained in 2007, the wetter year, and the lowest in 2008 (857,6 kg ha^-1) the driest one. It was possible to conclude that the last sowing date got the smallest yield. The other two sowing dates were similar though in many cases yield of the second date exceed the first one. In this unstable environment there was not a single parameter that will determine wheat yield. With good water availability grain weight was important to define grain yield and, on the other hand, in a drier year during grain filling the harvest index was associated with yield.