The effect of crop rotation and fertilization on wheat and maize in the pedoclimatic conditions of the Banat Plain

The simplification of the plant cultures range and the yields in the last 10-15 years brings into the actuality the role of crop rotation and of fertilization on the yield level and stability f or wheat and maize even on the soils with a high na tural fertility. The results of the researches performed between the years 2006 – 2009 on a cambic low gleyed chernozem from the Banat Plain showed t hat the wheat cultivated in monoculture gives productions with 59-81% lower tha n that cultivated in crop rotation with other plant s during 2-4 years. In maize, the yield obtained in monoculture is situated behind that obt ained in crop rotation with 11-21%. The most favora ble crop rotations for wheat were rape-wheat in a 4 years rotation and soybean-wheat in simple rotation of 2 years. In maize, the most f avorable was the 2 years rotation (wheat-maize). The mineral fertilization was very e fficient both in wheat (11-36%) and maize (9-31%). The organic fertilization with manure was very efficient for maize, the yields being supe rior with a mean value by 34% for a 60 t/ha dose an d with 16% for 30t/ha. The fertilization compensates the negative effect expressed by the mo nocultivation only in a small measure.


INTRODUCTION
In the last 10-15 years it can be observed a reduction of the plant number that is cultivated in all countries of Europe and in an accentuated way in Romania (Borza and Coste, 2002;Borza et el., 2006;Marinca et al., 2009). The main cause is represented by the express demand for cereals (wheat and maize) required by the animal breeding complexes in relation with the continuing decreasing animal effectives from the household system (Borza and Coste, 2002;Marinca et al., 2009). In the condition of a decreasing number of the plant cultures within the vegetal farms to only 3-4 plants, their rotation was simplified to an interval by 2-4 years and the monocultivation is performed on at least 25-30% surfaces for wheat and 30-40% for maize. In monocultivation, there is relying on the mineral fertilization contribution, in augmented amounts, and on the phytosanitary treatments, with much larger costs. The research results, as well as those found in production showed that even when the fertilization is increased, the monoculture is under crop rotation with up to 30-50% from yield in wheat and in a small measure in maize (Borlan et al., 1999; Borza et el., 2006).
On the soils with low natural fertility and in the years with less favorable climatic conditions for wheat crop, the yield results obtained in monocultivation are totally unsatisfactory. The organic fertilization is performed on extremely reduced surfaces, and in many farms is excluded because of the orientation of the agriculture system to the animal breeding in large complexes by industrial type. The relinquishment to the organic fertilization of the agricultural lands puts in danger their fertility even in the condition of a well balanced mineral fertilization (Borlan et al., 1999;Borza et el., 2006;Marinca et al., 2009;łărău et al., 2008).

MATERIAL AND METHODS
The researches were carried out during the years 2006-2009 on a cambic low gleyed chernozem within the Didactic Station of the University of Agricultural Sciences and Veterinary Medicine of Banat (USAMVB) from Timişoara, Romania, the soil being representative for approx. 10-15% of Banat Plain.
The experiments, in number of two, are stationary, with the following factors and ranges: crop rotations and various doses of mineral fertilizers, respectively crop rotations and increasing doses of manure.
For wheat, there were cultivated autochthon kinds, and for maize there were cultivated Pioneer hybrids. The mineral fertilization was realized with ammonium nitrate and complexes fertilizers 1:1:0 and 1:1:1, and the organic fertilization with semi-fermented manure from the bovine farm, applied before the maize cultivation.
The yield results are related to the STAS humidity, respectively 14% for wheat and 15% for maize, and the data processing was made by analysis of the variance with appropriate soft.
The researches continued in the year of 2010 and in the next years it is intended to be monitored not only the yields, but the soil fertility evolution too, as a consequence of the systematic application of the mineral and organic fertilizers.

RESULTS AND DISCUSSION
The characteristics of the cambic low gleyed chernozem from the Didactic Station of the (USAMVB) Timişoara, in the experimental location, were identified by opening a soil profile and can be found in the table 1. The pH has values between 6 in the Ap horizon and 6,7 in the Am horizon, fact that indicates a low acid reaction in the first 50 cm topsoil, the humus supplying in the Ap horizon is good, the phosphorous supplying is middle to good (35 ppm), the potassium supplying is very good in the Ap horizon (322 ppm), the apparent density is 1,54 g/cm 3 which shows an advanced compaction degree, and the total porosity is by 38,65% which denotes a compacted soil. Generally, the soil has a high fertility potential.
After the capability classification was settled that the studied soil is framed in the class of 61-80 points, being favorable both for wheat and maize. As fertilization requirements it reclaims the periodical application of the manure and an annually chemical fertilization in moderate and balanced doses, with special attention to the nitrogen-phosphorous ratio.
Under climatic aspect, the researched area is characterized by a multiannual mean temperature by 10.9 °C and a precipitation sum by 623 mm (Meteorological Station Tiumişoara). In the experimental years 2006-2009 there were registered differences both regarding the multiannual means and for each year (table 2). Table 2 The The analysis of the yield results depending on the experimental factors that were studied (crop rotation and fertilization) shows significant aspects which lead to valuable scientific and practical conclusions.
In wheat, the mean yields for four research years oscillated between 2083 and 5208 kg/ha, varying with the crop rotation and with the applied fertilization (table 3). Comparing to the monocultivation, the crop rotation by 2 and 4 years increased the wheat yiled with 1497-2076 kg/ha, respectively with 59-81%. The most favorable rotation was that of 4 years when the wheat followed after rape. In the 2 years rotation, the wheat behavior was the same after soybean and respectively after maize, excepting the unfertilized variant where the soybean proved that is superior to the maize as a precursory plant for wheat. The yield results on years show that the wheat production in monocultivation decreased after the second cultivation year, even if this is appropriately fertilized (figure 1). The effect of the mineral fertilization consisted of wheat yield increasing with 255-1147 kg/ha, respectively with 11-36%. The effect of the nitrogen applied all-alone was small (11%), but it was more significant in the presence of the phosphorous (2:1 ratio) and potassium (2:1:1). The optimal fertilization variant for wheat was N 120 P 60 K 60 for which there were registered a mean production in four years by 4585 kg/ha in the 2 years rotation after the maize, 4588 kg/ha in the 2 years rotation after the soybean and 4970 kg/ha in the 2 years rotation after the rape. In maize, it was found a positive influence on the yield both of the crop rotation and fertilization (table 4). Related to the monocultivation, the rotations of 2 and 4 years proved to be more favorable, being obtained mean growths comprised between 659-1248 kg/ha, respectively by 11-21%. The most favorable proved to be the 2 years rotation which has as precursory plant the wheat. The soybean, as precursory for the wheat assured a production increase by 11-12% in the rotations of 2 years and respectively 4 years. It can be remarked that the maize production in monocultivation did not decreased, the yield differences between the researched years were determined by the climatic conditions ( figure 2). The mineral fertilization led to the maize yield increasing with 481-1808 kg/ha (growth by 9-31%) related to the fertilization level. The nitrogen applied all-alone determined an increasing by 481 kg/ha (9%). Very significant yield growths were registered only at large doses of nitrogen in combination with phosphorous (N 120 P 60 ) and with potassium (N 120 P 60 K 60 ) for which the increasing are by 22% and respectively 31%.
The organic fertilization with manure applied to the maize proved that it is very efficient, being obtained mean yield growths by 992 and 2064 kg/ha at 30 and 60 t manure/ha (table 5).