Effect of composts, on growth and on yield quality of two crops, in a organic experimental farm of Southern Italy
Verrastro, V., El Hanafi Sebti, K.1, Hewidy M. Ramadan, M.1, Diacono, M.1,
Cocozza, C, Miano, T2.
Key words: Organic Agriculture; Compost; Nitrate Accumulation; Yield Quality.
Abstract 
Soil management in Organic Agriculture (OA) aims to improve the soil fertility (SF) supplying exogenous Organic Matter (OM) with composted and not – composted material. Hence, a two-year field experiment was carried out on a experimental farm of the Mediterranean Agronomic Institute of Bari (IAMB) in Apulia Region, Italy, to evaluate the effects, on organically cultivated plant growth and quality (as nitrate accumulation – nitr), of Compost (Comp) also in comparison to commercial organic fertilizers. Our investigations, in particular, aimed to evaluate the influence of Comp on Broccoli crop (Brassica oleracea var. Italica) cultivar Canoe and two varieties of tomato (Solanum lycopersicum Mill var. Vespro and Multiplo). However, despite our broad results, more studies need to improve common knowledge about Comp effects especially for OA management.
Introduction 
In OA, SF is defined as the ability of a soil to provide the optimal conditions for plants growth. According to EU Regulation 2092/91 annex II part A, among the strategies that farmers can use for maintaining or increasing SF, there is the incorporation of exogenous OM as composted or not composted material. In fact, OM is the main tank of organic carbon (OC) in terrestrial ecosystem and is an important source of nutrients for plant and microbial growth. The pool of stable and mature organic compounds (humus) is able to increase soil cation exchange capacity, buffer capacity, redox potential and availability of nutrients. It improves also soil structure enhancing water holding capacity and air movement in soil. Through composting, organic materials  undergoes a partial mineralization and, at varying degree, transformation into humus-like substances (De Bertoldi et al., 1983). The use of Comps for soil amendment can improves soil physical, chemical and biological fertility because the actions explained by these materials are similar to those explained by natural humus in soil. Hence, in order to investigate the effects on organically cultivated plant growth and quality (i.e. broccoli crop. var. Canoe and tomato var. Vespro and Multiplo), of Comp, two field experiments on a farm of the IAMB were carried out, during 2004/05 and 2005/06 respectively.

Materials and methods 
The study was carried out in the experimental field of the IAMB located in Apulia Region, in Southern Italy (72 m above the sea level, latitude 41°03’16’’ North and longitude 16° 52’ 45’’ East Greenwich). The region is characterized by a Mediterranean climate with hot dry summer and rainy mild winter.
At the beginning of each cultivation cycle, soil samples from the experimental area (at 30 cm depth) were taken and then prepared for physical and chemical analysis. Each sample was air-dried, thoroughly mixed and grounded to pass through a 2 mm sieve. The following selected soil characteristics were determined (table 1): the pH in 1:2.5 (weight/volume) soil/water suspensions, using a glass electrode pH–meter; available nitrogen (N) according to the method described by Keeney and Nelson (1982). OM content was analyzed by means of Walkley and Black method. Sodium and potassium were determined according to Black et al. (1982) and available phosphorus (P) was determined by using the stannous chloride method described by Jakson, 1967.
Different commercial Comps in each year were applied. The Comp (C1) used during 2004/05 was obtained from pruning and manure, and then mixed to peat at 1:1 ratio. During 2005/06, instead, we used another Comp (C2) obtained from the organic fraction of municipal solid waste and gardening residues. Table 2 shows the analysis of these products. The choice was made according to products availability and need for nutrients of each crop and taking into account the EU regulation 2092/91 and the national law.
The Comps were compared with two fertilizers (allowed in OA), one for each year: the fertilizer used in the first one was Guanito (G), composed from guano (a substance derived from birds and bats excrements), with the addition of AUXYM (composed of humic acids, vitamins, amino acids and plant hormones). Another fertilizer (BIO-REX) obtained by mature cow, horse and poultry manures, was used for the second trial.
The two varieties of tomatoes (Solanum lycopersicum Mill var. Vespro PS F1 and Multiplo F1) used are hybrid with medium growth cycle. The tomato seedlings were planted on May 2005; the spacing among plants was 30 cm, whereas the space among rows was 1 m. The experimental design for tomato trial was a split plot with 2 plots for treatments and 1 for the control (T1) as non –amended soil, for each variety. The soil treatments were: a) C1 and b) G. The C1 was applied one week prior to transplanting, as 25 t ha-1 incorporated in the 30 cm of the surface layer of the soil. The G was applied one week after transplanting superficially as 0.8 t ha-1.
The broccoli cultivar (Brassica oleracea var. Italica), used in the second year of the study, was “Canoe” which has big heads. The seedlings were transplanted on March 2006 and the plant spacing was 30cm x 100cm. The experimental design for broccoli trial was a randomized complete block designed with 4 treatments, one control, and 4 repetitions. The soil treatments were: a) C2 (as 20.7 t ha-1); b) C2 (as 10.3 t ha-1) + BIO-REX (as 1.37 t ha-1); c) BIO_REX (as 2.74 t ha-1); d) Control (T2).
Plants samples were taken in both trials from each treatment for measuring the quantitative and qualitative parameters, in order to assess the effects on organically cultivated plant growth and on yield quality. Two parameters were measured for both crops: yield and nitr content in the marketable product.

Tab. 1: Chemical and physical analysis of soil*. 
Sand
g/kg	Clay
g/kg	Silt
g/kg	pH(H2O) 1:2.5 g/kg	pH(CaCl2) 1:2.5 g/kg	Tot carbonate g/kg	Active Ca
mg/kg	
493	261	245	8.36	7.78	472.6	133.3	
OC
g/kg	OM
g/kg	N tot
g/kg	C/N	Available P
mg/kg	Available P2O5 mg/kg		
9.1	15.67	0.88	9.96	7.6	31.1		
*Sandy Clay Loam, USDA texture

Tab. 2: Chemical analysis of commercial composts.
	Humidity (%)	pH
in (H2O 1:10)	EC
ds/m	OC
g/Kg	Ntot
g/Kg	C/N	TotP (P2O5)
g/Kg	
C1	64.3	7.9	0.75	276.1	16.7	16.5	22	
C2	50	7.5	1.8	250	14.5	17.2	7.5	
	Tot K (K20)
g/Kg	Cd
mg/Kg	Cu
mg/Kg	Ni
mg/Kg	Pb
mg/Kg	Cr
mg/Kg	Zn
mg/Kg	
C1	15.8	1.1	81.4	58.4	40.9	65.0	129.7	
C2	9.5	1	100	50	1	100	300	

Results
Fig 1 gives the average yield (t ha-1) of the 3 blocks in the tomato trial and presents the marketable yield for broccoli crop showing clearly the good effect of BIO-REX when it is applied alone or combined with C2.
Table 3 shows the response to treatments of the two tomato varieties, regarding nitr accumulation in fruits. Vespro tended to accumulate more nitrs after each treatment than Multiplo variety.
On the other hand, the results for the trial carried out during 2005/06 with broccoli crop, indicated that the highest nitr accumulation was obtained after BIO-REX treatment.

Tab. 3: Nitrate accumulation in tomato fruits and in broccoli heads.
Tomato var. Vespro	Tomato var. Multiplo	Broccoli	
T1	C1	G	T1	C1	G	T2	C2	BIO-REX	C2+BIO-REX	
278.4	215.0	256.4	162.8	94.5	191.3	47.2	38.7	59.0	27.5	

Figure 1: Effects of different treatments on tomatoes and on broccoli yield.
Discussion 
The results for tomatoes yield emphasize that the amendment with C1 and G had the same effect on the plant growth. The positive effect of G could probably be explained to its AUXYM content that increased the yield. Moreover, the positive effect of C1 on yield might be due to its OM content that improved chemical, physical and biological properties of soil, and to its release of both macro and micronutrients, which is in harmony with the findings of Togum et al. (2002). The results for broccoli yield are explained by the rapid availability of nutrients which were supplied by the commercial fertilizer in comparison with a low rate of mineralization and nutrient release of the C2.
One of the most important quality parameters is the NO3–N content in marketable vegetal products that determines the edibility of the product itself. The higher nitr accumulation in tomato fruits var. Vespro, in comparison to var. Multiplo, could be explained by the different ripening stage at the harvest time. C1, however, has induced a low nitr accumulation in comparison to control. Moreover, there is no notable difference between T1 and G, in respect of the response of the two varieties, which could be probably explained because of G doesn’t clearly influence the nitr content in tomato fruits. In the second experimental trial, the lowest value for nitr accumulation was noted for C2 + BIO-REX treatment, probably due to good efficient of living microorganisms in soil (due to C2 effect) which manage nitrogen mineralization.
References 
De Bertoldi M., Vallini G., Pera A. (1983): The Biology of composting: a review. Waste Manage Res., 1:157-176.
Togum et al. (2002): Growth, nutrient uptake and yield of tomato in response to different plant residues composts. Food, agricultural and environmental (JFAE). Vol. 2. WFL publisher.
El Hanafi Sebti, K. (2005): Compost tea effects on soil fertility and plant growth of organic tomato (Solanum Lycopersicum Mill) in comparison with different organic fertilizers.  Collection Master of Science n.405, Mediterranean Agronomic Institute, Italy. 
Hewidy M. Ramadan, M. (2006): Different organic fertilization effects on organically cultivated broccoli (Brassica oleracea var. italica). Collection Master of Science n.443, Mediterranean Agronomic Institute, Italy.