Conclusion and perspectives

Biomass production is significantly influenced by many environmental, agronomic and other factors. The most important of them are air and soil temperature, soil humidity, photoperiod, light intensity, genotype, and soil nutrient availability. Soil fertility, i. e. the availability of nutrients in the optimum concentration range, greatly influences biomass production. If nutrient concentrations are out of the optimum limits, i. e. in the cases when nutrient deficiency or toxicity occurs, biomass production is depressed. Under nutrient deficient conditions, the farmers use chemical fertilizers in order to enhance yields and fruit production. However, since the prices of fertilizers have been significantly increased during the last two decades, a very good agronomic practice is the utilization of nutrient use efficient genotypes, i. e. the utilization of genotypes which are able to produce high yields under nutrient limited conditions. Although great scientific progress has been taken place during last years concerning nutrient use efficient genotypes, more research is still needed in order to clarify the physiological, genetic, and other mechanisms involved in each plant species.

On the other hand, in heavy metal contaminated soils, many plant species could be used (either as hyperaccumulators, or as fast growing-high biomass crops) in order to accumulate metals, thus to clean-up soils (phytoremediation). Particularly, the use of fast growing-high biomass species, such as Poplar, having also the ability to accumulate high amounts of heavy metals in their tissues, is highly recommended, as the efficiency of phytoremediation reaches its maximum. Particularly, since a given species typically remediates a very limited number of pollutants (i. e. in the cases when soil pollution caused by different heavy metals, or organic pollutants), it is absolutely necessary to investigate the choice of the best species for phytoremediation for each heavy metal. In addition to that, more research is needed in order to find out more strategies (apart from fertilization, the use of different Bacillus sp. strains, CO2 enrichment under controlled atmospheric conditions e. t.c.) to enhance biomass production under heavy metal toxicity conditions, thus to ameliorate the phytoremediation efficiency.

Author details

Theocharis Chatzistathis[20] and Ioannis Therios

Laboratory of Pomology, Aristotle University of Thessaloniki, Greece

Means followed by a different letter lower-case letter, in the rows, and capital letter, in the columns, are different [Comparisons among means were made according to Tukey-Kramer and F’ tests (p < 0.1), respectively].

[2] Cane was planted on 01 Mar 2001

[3] Treatments were: Control (no N fertilizer applied), AS15N (15N-labeled ammonium sulfate); SH + AS15N (Sunn hemp + 15N-labeled ammonium sulfate); SH15N (15N-labeled Sunn hemp).

[4] Standard error of the mean. Adapted from [12].

Table 13. Percentage (Ndff) and quantity (QNdff) of nitrogen derived from the labeled fertilizer source,

nitrogen recovery (R) in sugarcane stalks and nitrogen accumulated in samplings carried out in the first

and second harvestings1.

In the present study, about 69% of the N present in the sunn hemp residues were from BNF.

The data obtained in the present study are also in agreement with those obtained by [18] for

green manure produced in the field, in the inter-rows of the ratoon crop.

Perin [32] found substantial amounts of N derived from BNF present in the above ground

parts of sunn hemp (57.0%) grown isolated and 61.1% when intercropped with millet (Pennisetum glaucum, (L.) R. Brown) (50% seeded with each crop). The sunn hemp+millet

treatment grown before a maize crop resulted in higher grain yield than when sunn hemp alone was the preceding rotation. This effect was not observed when N-fertilizer (90 kg N

ha-1) was added; Perin [32] concluded that intercropping legume and cereals is a promising

biological strategy to increase and keep N into production system under tropical conditions.

No difference was observed in relation to the cumulative N listed in Table 10. The cumulative N results are similar to those found by [47], who obtained, during plant cane harvesting, mean values of 252.3 kg ha-1 cumulative nitrogen, with high nitrogen and plant material

[17] See http://satoyama-initiative. org/en/ for more details.

[18] Corresponding Author

[19] Corresponding Author

[20] Corresponding Author