Conservation Agriculture Based on Direct Sowing

Abstract

A research development initiative at the farm level was conducted within the framework of a service contract between ESAK and the GCP/TUN/028/ITAFAO Project in Siliana Governorate at three sites (Hamzet, Kharrouba and MnaraRjeybia). The project sought to encourage cereal producers to adopt a conservation-based agriculture using direct sowing (DS) in agricultural lands known to have a high risk of water erosion. An agro-climatic characterization and one growing season (GS) study (2003–2004) of edaphic and production parameters was carried out. An agro-climatic characterization of ten GSs (1993/1994– 2002/2003) showed that grass cereals grew in water deficient conditions during their entire growth cycle under rainfed conditions, which requires sowing in late December when the evapotranspiration (ET) curve approaches the rainfall curve. Barley (Hordeum Vulgare L.) appeared to be the most efficient cereal species in terms of water use (4.8 kg mm). Rainfall in autumn, winter and spring provide an opportunity for agronomy (two crops per year under rainfed conditions), whenever an agronomic scenario is appropriately set up. The rate of water infiltration was greater by 58%, 12% and 56% with DS compared to conventional sowing (CS), in Hamzet, Kharrouba and Mnara-Rjeybia, respectively. The apparent soil density and soil porosity, two indicators of soil quality, were in favour of DS. However, water dynamics associated with the soil was variable among the experimental sites and growing periods with a general trend revealing DS to perform better in terms of water retention, especially during the grain filling period (June). Phyto-toxicity expressed by a prior allelopathic cereal-species/variety could be a major constraint for DS. Therefore, the choice of an appropriate rotation, based on an agronomic sequence of a least depressive cereal-species/variety to a subsequent tolerant cerealspecies/variety, remains an efficient agro-physiological approach (technique of bioassays) to reduce the effect of phyto-toxic residues for DS. Adoption of DS remains essentially related to how much more grain is yielded (quintals ha) compared with CS. For the 2003–2004 GS, durum wheat (Triticum durum L.) grain yields 1 Ecole Superieure d’Agriculture du Kef (ESAK), Le Kef, Tunisia 2 Centre Technique des Cereales (CTC), Tunisia 3 Governmental Cooperative Project/Tunisia/028/Italy-FAO, Tunisia C. Lee and T. Schaaf (eds.), The Future of Drylands. 647 © UNESCO 2008 648 M. Ben-Hammouda et al. were greater by 12%, 33% and 9% in DS compared to CS, for Hamzet, Kharrouba and Mnara-Rjeybia, respectively. Any grain yield increase coupled with an increase in hay yield (bales ha), as in the case of Hamzet (263 bales ha vs. 169 bales ha) and Mnara-Rjeybia (336 bales ha vs. 325 bales ha), would motivate cereal growers to raise animals while practicing DS.