Tunisian climate is mediterranean, characterized by irregular, sudden, intense and relatively low rain-fall. Land degradation is continuing, water resources are becoming scare, and energy cost of farm products is continuously getting high. Consequently, cereal producers can hardly make an economic return, while practicing conventional agriculture based on conventional drilling (CD). Conservation agriculture based on direct drilling (CA/DD) gives farmers a chance to protect soils and rebuilt their fertility for an efficient use of any available form of water (rain-fall, irrigation). Such desirable efficiency does not come only by the use of the appropriate crop species, but necessarily by reducing water evaporation. To do so, a permanent mulching on the soil surface is the pivot of CA/DD. Since rain-fall fluctuates from one year to another, crop sequences should parallel with such conditions. Some couloirs have early rains (September-October) and late rains (May-June) too. In Bou-Salem (Governorate of Gendouba), early and late rains accounted for 26.2 % and 19.9 % of the 07/08 total rain for cereal growing season (September/07-June/08), respectively. These rains are not well capitalized in cereal production, when applying conventional agriculture. So, coupling the site specific approach and agronomy of opportunity is imperative to lift up farm productivity. The climate (rain, heat) of production sites should be characterized to better define growing seasons and make the appropriate agronomic sequence. Then, the agronomy of opportunity (producing the maximum of biomass whenever the climate and the biology of the desired crop are favorable) could be applied in different scenarios, under rain-fed and/or irrigation conditions. There is no static scheme to crop the land, and it is rather a dynamic management of soil, crops, and water. A particular emphasis should be put on use of strictly seasonal (fall, winter, spring, summer) cereals and legumes in order to make a continuing cropping with two-three crops a year. A potential scenario could be a fall-barley/springpeas/ summer short season-sorghum hybrid.

TP content could explain partially the auto-toxic potential of barley, leaving the eventuality of other allelochemicals to be implicated in. Auto-toxic potential was not stable over time, indicating that is not highly genetically controlled. In fact, a relatively dry 00/01 GS, characterized by the highest concentrations of phenolic acids in BP tissues, was the sole GS that showed a significant relationship (r = 0.42, p < 0.10) between RG inhibition and TP and at the same time (r = 0.46, p < 0.8) between CL/RL ratio and TP, though the probability level in both cases was relatively high. Three phenolic acids (POH, SYR, PCO) were found to be involved significantly in the expression of barley auto-toxicity. The most present phenolic acid (VAN) in barley plant tissue did not show an individual significant role in barley auto-toxicity, suggesting rather a synergetic effect with one or more implicated phenolic acids. Also, the less frequent phenolic acid (FER) was the sole involved with CL/RL ratio, suggesting that its effect is a differential allocation of dry matter in favor of barley shoot growth. ‘Rihane’ was the sole barley variety of which TP content was significantly correlated to barley auto-toxicity27/11/2014TP content could explain partially the auto-toxic potential of barley, leaving the eventuality of other allelochemicals to be implicated in. Auto-toxic potential was not stable over time, indicating that is not highly genetically controlled. In fact, a relatively dry 00/01 GS, characterized by the highest concentrations of phenolic acids in BP tissues, was the sole GS that showed a significant relationship (r = 0.42, p < 0.10) between RG inhibition and TP and at the same time (r = 0.46, p < 0.8) between CL/RL ratio and TP, though the probability level in both cases was relatively high.