Moreover, the profitability of this ecological system can be multiplied by four when an ecological market exists. This is what Gabriel Pardo Sanclemente from the Public University of Navarre states in his PhD thesis, Comparative study of fertilisation and weeding of the ecological cultivation of cereals on semiarid land. Ecological profitability ,Ecological systems of production of cereals are based on the rotation of crops, the use of natural organic additives and the mechanical control of weeds, in order to maintain the fertility of the soil and weeds in the long term and at reasonable levels. In his PhD, Gabriel Pardo Sanclemente specifically investigated the viability of ecological systems of production of cereals in semiarid land, a viability which depends on the yield of quality crops free from agrochemical waste products and for which a higher price can be paid, so that the gross profit margin of the crop yields is increased and, moreover, an agriculture more respectful of the environment is achieved. Thus, experiments were carried out comparing chemical methods of fertilisation and weeding using with the method recognised by the Regulations on Ecological Agriculture. The thesis centred on the results from 26 tests carried out in various semiarid land zones in Spain and on which barley, using vetch as green fertiliser, was rotated with wheat and fallow. From the results it can be deduced that the greatest profitability was obtained from the ecological system - organic fertilisation and the mechanical control of weeds. Following this was the minimum system without fertilisation methods or the mechanical control of weeds. Trailing behind and presenting the worst results in terms of profitability was the conventional system. Extrapolating from this data, Gabriel Pardo Sanclemente proposes the use of the minimum system for crop growing, carrying out the proposed rotation and burying of residues, given that this system does not significantly diminish production while reducing costs, thus profitability being increased. Unjustified use of fertilisers The thesis results demonstrate that, in the wheat tests, the average production rates from the fertilised and unfertilised plots are practically the same. With the tests on barley, the chemically fertilised plots produced on average 400 Kg./ha compared to the organically fertilised ones. A difference that is not significant for the author. Likewise, it was found that the high levels of organic material and initial phosphorous have been maintained after six years of testing - including in the non-fertilised plots -, with the level of potassium dropping slightly. This data suggests that the crop rotation carried out, together with the returning to the soil of the crop remains, has been sufficient to maintain the initial contents of the nutrients. Unnecessary weeding Regarding the weeding methods, both the use of the hoe and of herbicides were found to be unsuitable for increasing crop yields in the test conditions. Thus, the density was, in general, poor on those cereal plots after the lying-in-fallow or buried vetch period. However, the least density of weeds achieved after any weeding treatment mechanical or chemical did not give rise to any significant increase in grain production with respect to the control experiment.