EVOLUTION OF SOME COMPONENTS OF AGROECOSYSTEMS PRODUCTIVITY FROM VINGA PLAIN IN WATER STRESS SITUATIONS

The researches are inscribed on line of substantiation of durable agricultural system, having as main objective the prominence of quantitative and qualitative modifications made on agro-system level under the effect of no-tillage system for wheat, maize and soybeans. The experimental field is placed on a cambic chernozem, with a medium content of clay, dominant in the Prodagro West Arad agro-centre and representative for a large surface in the Banat-Crisana Plain. The passing to no-till system change the structure of technological elements, through less soil works, so the impact on agro-system is different comparing with conventional tillage, first less the intervention pressure on agro-system ant secondly appear new interactions, new equilibriums and disequilibriums. Considering the evolution of soil humidity, the observations made monthly (by taking soil samples and laboratory determinations) for the three cultures showed that in the no-till system, there are more uniform values in the soil profile, and in the variants where the deep work of soil was made it could be observed a low increase of the water volume in the soil.


INTRODUCTION
The experiment has three factors, being of the type 2x2x3, with subdivided parcels into 4 repetitions (144 parcels). The surface of one plot is of 27 sm (3x9), the total surface of the experiment being of 3888 sm.
The examination of ecopedological conditions, were made according to " The Pedological Studies Elaboration Methodology ", (vol. I,II,III) of ICPA Bucharest, in 1987 and Romanian Taxonomic System of Soils (SRTS-2003).

RESULTS AND DISCUSSIONS
From the geomorphological point of view the perimeter on which are located the experiments belongs to the large physical -geographic unity called the Vinga High Plain.Vinga high plain is the oldest and the most complex among Banat-Crisana plains and extends south of Mures everglade , west of Lipova hills, north of Bega low plain , east of Galatca plain. It is formed at the convergence of hills glacisist, shaped by a net of flowing waters and erosion valleys (łărău D, et all, 2003).
The area where the experiment was placed is in the North-Western part of the High Plain of Vinga, above the 3rd terrace of Mures river, on the alignment New Tisa, Felnac, Secusigiu, at 100 -120 m height and it has an aspect of tabular plain with cvasi-horizontal surfaces on which there are many small micro depressions and valleys.
Hydrographically, the perimeter where the experiment is placed belongs to the hydrographic basin of Mures river which flows at about 2-3 km north from this. The pedo-phreatic levels are at 5,1 -10 m depth (they don't interfere in the pedo-genesis processes) in flat areas and between 1,5 -3,0 m depth in the valleys (łărău D, et all, 2003).
The climate is a temperate-continental one with Mediterranean influences, the medium multi-annual temperature being of 10,4 0 C (table 1) and the multi-annual rainfall 593,5 mm (table 2). Regarding rainfall, due to cyclonic activity and the invasions of moist air from the west, southwest and northwest, rainfall within the area studied are quantitatively higher than in other low plain areas (with similar altitude) of Romania, the specific of these area is determined by the Baric movement and relief characteristics and the annual average recorded value of 593.5 mm, with large swings from year to year, 405.1 mm in the 1999-2000 agricultural year and respectively 741.6 mm in the 2004-2005 agricultural year (tab 2). To assess the impact of weather on different agricultural systems, the precipitation data were compared with the significance of rainfall (reference range compared with the requirements of agriculture) being used data from Agroclimatic Resources of Timis county (Table 3). Table 3 The significance of rainfall (mm) in relation to the requirements of agriculture As a result of the cosmic-atmospheric and telluric factors intervention, under a specific vegetation to the forest steppe, in the zone were created cambium chernozems, specific to the researched perimeter.
The analyzed soil has an acid reaction (5,9 -6,8) in the first 80 cm of the soil profile, neutral between 80-125 cm and low alkaline between 125 -200 cm depth.
The mobile phosphorus content (P) in the worked soil (Ap) has medium values (35,0 ppm) at the limit of alert threshold (concerning the nutrition lack) the mobile potassium supply (K) having medium values (153 ppm), values which are lower on with the profile.
The humus reserve in the first 50 cm is high, and the natrium index (I.N.) has medium values in the worked layer (Ap) and also in the 0 -45 cm layer.
Soil's texture, a very stable physical feature, is medium clay on the whole profile. The Apparent Density (DA) has medium values in the worked layer from the classic system, high in the first 10 cm in no-till system and very high in the middling third of the soil profile in the two systems.
The Total Porosity (PT) has low values in the 0 -33 cm interval, and also in the 45 -96 cm one. The aeration porosity, which represents all the pores occupied with air when the soil is in optimum humidity conditions, has very low values, excepting the worked layer from the classic system, where it has low values and the first 10 cm depth in No-till system where the values are very low.
After establishing the cultures, among the specific maintaining works there were made a series of observations in order to identify and stock take the main damaging species from the vegetal or pathogen flora and fauna, which frequently populate the wheat, maize and soybeans agro-ecosystems. The field cultivated as No-Till system is exposed to a higher degree of weeding compared to the classic one. The plants that developed in the wheat, maize and soybeans cultures had an easy progress, especially those which multiplicate vegetative or by seeds (Cyrsium arvense L., Convolvulus arvensis L., Sonchus arvensis L., Cynodon dactylon L., Sorghum halepense L., Rubus caesius L.) or with small seeds and surface germination (Stellaria media L., Capsella bursa pastoris L., Lamium purpureum L.) and infesting those that develop widely in the stubble (Setaria sp., Polygonum convolvulus L., Matricaria inodora L., Rubus caesius L).
Considering the evolution of soil humidity, the observations made monthly (by taking soil samples and laboratory determinations) for the three cultures showed that in the no-till system, there are more uniform values in the soil profile, and in the variants where the deep work of soil was made it could be observed a low increase of the water volume in the soil.
The wather reserve from soil, between 0-100 cm in 2007-2008 agricultural year (  (Table 7), comparing with field capacity values, are more less in all the experimental factors .   About the yields obtained from the three cultures, in 2007-2010 agricultural year, there can be remarked the followings:for wheat, the yield was between 3795-4292 kg/ha, the highest yield of 4292 kg/ha, being registered in the classic system without no deep work of soil, in N 160 P 80 K 80 dose and the lowest of 3795 kg/ha in the no-tillage system with the deep work of soil, in N 0 P 0 K 0 dose (table 8) . For maize the obtained yield had values of 5541-6458 kg/ha, the highest yield of 6458 kg/ha, being registered in classic system without deep work of soil, in N 160 P 80 K 80 , and the lowest of 5541 kg/ha in no-tillage system with deep work of soil, in N 0 P 0 K 0 . (table 9)  Table 9 Influence of the no-till system on to the maize crop on the cambium chernozem medium clayey earth/ medium clayey earth from Arad For soybeans the yield was 2998-3342 kg/ha, the highest yield of 3342 kg/ha being registered in the classic system with deep working of soil, in N 80 P 80 K 80 , and the lowest of 2998 kg/ha in the no-till system with the deep work of soil, in N 0 P 0 K 0 (table 10).

CONCLUSIONS
Considering the evolution of soil humidity, the observations made monthly for the three cultures showed that in the no-till system, there are more uniform values in the soil profile, and in the variants where the deep work of soil was made it could be observed a low increase of the water volume in the soil.
Even if the productions obtained in the classic system are superior than those obtained in the no-till system, considering the economical costs for establishing a culture in the no-till system are lower, the same as the pressure made upon the soil (by reducing the number of passes with the agricultural machines and installations), than the classic system.
The obtained production results can not give a recommendation for one of the two experimented culture systems, but they are valuable data (concerning the evaluation of the natural and manmade resources) by the studies made in the field and laboratory, for the fundament in the future of some adequate technologies for the climatic and soils conditions of the area where the research was made and also for other similar areas.