The main purpose of this work was to evaluate the possible use of humic
acid mixed with the irrigation water through a drip irrigation system to
alleviate the harmful effects of salinity stress on growth, fruit yield and quality
of tomato plants (Lycopersicon esculentum, c.v. 1077 hybrid). To achieve this
target a field experiment was carried out on a private farms at Sedmant El
Gabal village, Beni-Suef Governorate, Egypt, which represents one of the
those are occupying the desert zone adjacent to the western edge of the Nile
Valley during two successive seasons of 2005-2006 and 2006-2007. Two
irrigation water resources were used, i.e., the Nile water (C1S1, ECiw = 0.56
dS/m and SAR = 2.13) and a mixture of agricultural drainage saline water with
the Nile water at a ratio of about 1:1 (C2S1, ECiw = 1.89 dS/m and SAR =
5.35). Humic acid was applied at rates of 75, 150 and 225 mg/L through a drip < br />irrigation system twice/week and for a period of 4 months after transplanting.
The obtained data reveal that the studied soil is mainly encompassing
the wind blown sand deposits as a parent material, and it is classified as
Typic Torripsamments, siliceous, hyperthermic and it could be evaluated as
marginally suitable. The results also show that usage of saline water resulted
in relative increases of the ECe and ESP values in the root zone reached 18.95
and 33.09 % as compared to the initial state of soil, respectively. Meanwhile,
the corresponding relative increases of the ECe in case of amended saline
irrigation water with humic acid at rates 0. 75, 150 and 225 mg/L were 11.75,
5.09 and 2.98 %, vs 10.84, 3.76 and 1.73 % for the ESP values, respectively,
with its optimal case at a rate of 225 mg/L. Moreover, the applied humic acids
played an important role in improving the values of soil bulk density, total
porosity, available water and hydraulic conductivity, organic matter content,
pH, CEC and available nutrients. The latter may be due to modified airmoisture regime that leads to alleviate the depressive effect of salinity stress
on the released nutrient from organic residues.
These favourable conditions of the improved soil due to amended
irrigation water positively reflected on the vegetative growth and flowering
parameters of tomato plants, i.e., plant height, number of leaves/plant,
thickness of stem/plant at soil surface, number of branches/plant, leaf area,
number of inflorescences/plant, number of flowers/inflorescence, dry
weight/plant, and the chlorophyll a & b contents. It is evidently that such
beneficial effect of humic acid on the dry matter productions was more
attributed to the leaves area and number, which are contributed to more
photosynthesis and better carbohydrates yield. Also, the ability of humic acid
for increasing plant nutrient uptake is due to its chelating property. Moreover,
the applied humic acid at all the different rates resulted in significant increases
for N, P and K in tomato leaves. The reverse was true for Na and Cl, probably
due to alleviate the harmful effect of saline irrigation water. In addition, using
humic acid at the rates of 150 and 225 mg/L mixed with saline irrigation water
registered almost similar tomato yields to those irrigated with the Nile water
and higher than those irrigated with either saline water or treated with at a rate
of 75 mg/L humic acid. The relative increases in fruit yield/plant or fed could
be attributed to significantly higher increments in dry weights and number of
flowers/plant. The parameters of tomato fruit quality, i.e. average weight of
fruit, fruit firmness, total soluble solids (TSS), vitamin C (ascorbic acid),
titrable acidity (citric acid) and total sugar showed significantly increased
when treated with amended saline irrigation water with humic acid at the
applied rates as compared to the effect of used saline water solely. Thus, the
present study shows that the best rate of the applied humic acid mixed with the
used irrigation saline water was 150-225 mg/L for achieving the greatest
tomato yield of high quality.