– Volume 20 ( 2014 ) No . 2 55 RESEARCH ON THE STRUCTURE AND CHEMICAL COMPOSITION OF SOME STRAINS OF VEGETABLE CROPS

This paper presents the results from the analysis of the structure and chemical composition of 15 strains of crops subjected to cutting operation. The experiments consisted of EDAX analysis (Energy Dispersive X ray Analysis) for identifying the chemical composition of the samples and a microscope electron scanning to obtain the structure -sectional evidence. The results may be related to resistance to cutting of stems, in order to establish correlations between these and their chemical composition, but also for later use of them as plant debris.


INTRODUCTION
Cutting plant stems is an operation with significant energy consumption, and this requires the use of appropriate cutting equipment for each culture [1].
The structure and chemical composition depends on the species and stem aging at the time of the harvest [2].A link between these elements and cut resistance has not been established and therefore a first step in this direction may provide such analysis.
Strains have various forms after their environment, orientation in space and their functions.Most plants have straight stems, with well-developed supporting tissues.Such strains compose the majority of crops and herbaceous plants [3][4][5][6][7].
The strains are structurally diverse, from those without marrow inside and exterior cell structure to those with dense marrow or less dense, respectively, with exterior cell structure [4], this is leading to different values of resistance to cutting.
We must also consider that as plant debris, stems can be a raw material in order to use them as energy and maybe even for soil improvement.

MATERIAL AND METHODS
To determine the structure and the chemical composition of vegetable stems, an electronic microscope Quanta 200 3D SEM/FIB has been used (Figure 1).EDAX analysis is a technique used to identify the basic chemical composition of a sample [5].It works as an integrated feature of a scanning electron microscope SEM.Thus, the sample is bombarded with an electron microscope in which electrons collide with atoms of the sample, extracting some of them.A vacant position of an electron from a lower level is occupied finally by a higher energy electron from a higher level, giving some energy in the form of X-rays.By measuring amounts of energy present in the X-rays released by the specimen during electron bombardment, it can be established the identity of the atom from which X-rays were emitted.The EDAX analysis generates a graphic spectrum that identifies the corresponding elements in each of its peaks and the type of X-ray [6].In this way, there are highlighted the chemical concentrations for each plant strains (Figure 2), as well as their structure.In the experimental research, there have been used 15 strains of agricultural crops at technological maturity, grown in the Bacau County, whose characteristics are shown in Table 1.
The stems were cut at the height of working apparatus cutting machines harvesting, respectively 15-20 cm above ground crops for grains, and 3-5 cm soil to forage plants Both diameter and strain moisture of field crops and fodder plants studied have values that are recorded at the time of their collection.

RESULTS AND DISCUSSION
Experimental results are presented as images (Figure 3 -Figure 8) of six types of stem structure, namely wheat, peas, soybeans and sorghum, and forage crops and two trefoil and red clover.As a result of structural analysis of the strains was found that for wheat, barley, oats and triticale, they are tubular in shape, without marrow on the inside and with exterior cell structure.For strains of soybeans, peas, beans, lucerne, red clover and trefoil, they present an exterior cell structure and a low-density marrow.For strains of sorghum, corn, rapeseed and sunflower there is a higher marrow density, and an exterior wood cell structure.
By analyzing the chemical composition of the strains (Table 2) it can be seen that these elements differ from one species to another, and for fodder, it differs from one vegetation phase to another.Only nitrogen, chlorine, phosphorous, carbon, aluminum and oxygen are the chemical elements that are found in all strains analyzed.
The chemical composition of strains highlights their possible use for soil improvement (1.49 % calcium for peas, soybeans with 1.05 %, 10.5 % phosphorus for oats, Sudan grass with 7.37 % and peas with 6.99 %).There is a high proportion of aluminum in red clover before flowering (3.03 %) and red clover after flowering (2.29 %).

CONCLUSIONS
Stems structure at harvest is characteristic of the species and within the same species, of the stage of vegetation, especially in the case of fodder.It may vary from stem free hollow core to dense marrow stems with exterior wooden structure.This has a direct effect on the process of cutting during harvest and in particular on the work needed for cutting.

Figure 7 .
Figure 7. Structure of sorghum stem.Figure 8. Structure of red clover before flowering.

Table 1 .
Stem characteristics subjected to EDAX analysis.

Table 2 .
Chemical composition (in %) of plant stems determined with an electronic microscope.