Irrigation , a Basic Technological Element , for Improving the Autumn Cabbage Yield in Crișurilor Plain , Western Romania

The researches were carried out at the Agricultural Research and Development Station, Crișurilor Plain, Oradea, during 1990-2016. They have demonstrated that irrigation is needed every year due to the extension of the drought regions in Romania. Irrigation has become a basic element in the technology of the autumn cabbage crop due to the yearly pedological drought. For cabbage, the minimum watering depth is considered 0-50 cm, while an irrigation average rate of 2,410 m/ha, with a variation range of 1,330-4,900 m/ha had to be imposed in order to maintain the soil moisture content on the watering depth between the easily available water content and the field capacity. Irrigation improved the microclimate conditions and the ratio water/temperature + light (Domuţa climate index) increased. Daily water consumption increased as well. As a result, total water consumption increased by 70%, with a variation range of 19-872%. Irrigation determined an yield gain of 153%; water use efficiency (kg/m) increased by 60.0%; irrigation water use efficiency recorded an average value of 13.4 kg yield gain/m, with variation range 6.7 kg yield gain/m-24.2 kg yield gain/m. The correlations quantified in the soil-water-plant system (number of days with pedological drought, yield, respectively yield gain; Domuţa climate index-yield; water consumption-yield) support irrigation for the autumn cabbage crop from Crişurilor Plain.


Introduction
A great number of vegetable species, varieties and forms are important elements for a wide range of food with valuable ingredients, significantly improving and enriching meal choices (Posta and Berar, 2007).Staggered production cycles and the constant need to supply markets with fresh vegetables have become crucial issues.Adding various vegetables to daily meals has to be possible all year round, not only during the top harvesting seasons.Besides supplying markets with fresh products, vegetables are also important as raw materials for the food industry (Laczi et al., 2014).
The origin of the cabbage is the basin of the Mediterranean Sea.It was harvested in Antiquity by Greeks, Romans and Chinese.Western and Eastern Europeans have been harvesting it on large scales since the 11 th -12 th centuries.Cabbage can be consumed in many forms (fresh, pickled, dried or frozen) thanks to its content in vitamins (A, B1, B2, C, PP, K) and mineral salts (Ca, Fe, Cu, P, Zn, Cl, Na) (Csok et al., 2007;Stoleru and Imre, 2007).
Cabbage requires a high amount of water.Domuța (2008) highlighted the correlation between water requirements and production levels (Frantz et al., 1999;Apahidean et al., 2011).Compared to fruit trees, it was more difficult for leafy vegetables, including cabbage, to adapt to water deficit (Jones, 2004;Costa et al., 2007).Results of the influence of water deficit on cabbage yield presented several discrepancies due to differences in harvesting, climate, soil and irrigation method.
ETc is defined as the amount of water required by a crop for optimal growth.Eto was determined using measured climate data and the required Kc factors were provided by the FAO for a multitude of plants (Allen et al., 1998).
For all these, researches on the irrigation of the autumn cabbage crops from Crisurilor Plain, a geographic formation in North-Western Romania, were initiated by Domuta in 1990.

Materials and Methods
Description of the study site Researches were carried out at the Agricultural Research and Development Station from Oradea during 1990-2016.
The preluvo-soil from research site was well structured, the aggregates representing 47.5%.On the watering depth of the autumn cabbage crop, the soil had a wilting point of 9.7% (720 m 3 /ha) and the field capacity was 24% (1,787 m 3 /ha); the clay content determined the easily available water content at 2/3 of the ratio field capacity, wilting point.Its value was of 19.2% (1,431 m 3 /ha) (Table 1).Research soil presented a weak acid reaction on the entire studied depth, with values increasing from surface towards the depth (Samuel et al., 2011).The supply with humus was poor and also the supply with total nitrogen was poor ranging to average on the entire studied depth (Table 2).
The source for irrigation was a well that provided irrigation water with very good chemical properties (CSR = -187; SAR = 0.53 in 2007-2009) (Table 3).
Analysing the influence of fertilization by tank sprinkler and by drip irrigation on the white cabbage from sandy soils, Sturm et al. (2010) found out that the yield, the nitrogen uptake in the plant (246 kg/ha) and the efficient use of fertilisers registered significantly increased values when tank sprinkler was used as compared to drip irrigation.However, drip irrigation, which covered 100% of the crop's water requirements, did not ensure the highest yield due to the sandy soil the experiment was conducted on.
Compared to furrow irrigation, drip irrigation is the most effective method to irrigate vegetable crops thanks to water savings and yield increases (Tiwari et al., 1998a,b;Xie et al., 1999;Tiwari et al., 2003).
A study conducted on the cabbage growth and yield concluded that a water deficit at 50% ETc led to significant decreases of the yield, cabbage head size, fresh weight and relative water content as compared to a water deficit at 75% ETc (ETc -consumptive use of water, or evapotranspiration).Both cases indicated that the decrease of the marketable and total yield was influenced by the relative water content (Xu and Leskovar, 2014).
Analysing the effect of irrigation on the growth of white cabbage on a loamy sand soil near Dresden, Germany, Seidel et al. (2017)   The irrigation installation from the research site allowed a precise measurement and an even distribution of the irrigation water.

Experimental procedure
The soil moisture was determined every 10 days, using the gravimetric method on 0-50 cm depth and the neutron method on 50-150 cm depth.By means of irrigation, the soil water reserve was maintained at a depth of 0-50 cm above the easily available water content.The following formula was used to determine the water reserve: Wr = U × BD × H where: Wr = water reserve, m 3 /ha; BD = bulk density, g/cm 3 ; H = depth, cm.Domuța (1995) described the pedological drought using two indexes: pedological drought (the period with soil water reserve on watering depth below the easily available water content) and strong pedological drought (the period with soil water reserve on watering depth below the wilting point).In order to count the days with pedological drought below the easily available water content and below the wilting point, several graphs of the dynamics of the soil water reserve were set up based on gravimetric determinations of the soil moisture.
Water consumption was determined by the soil water balance equation; 0-150 cm depth was used for balance.The following formula was used: Ri + Pv = Rf + Σ(e + t) where: Ri = initial water reserve (at the planting), m 3 /ha; Pv = rainfall registered during cabbage planting and harvesting, m 3 /ha; Rf = final reserve (at harvesting), m 3 /ha; Σ(e + t) = total water consumption, m 3 /ha.
Harvesting and calculation of results were performed observing the instructions provided for such experiments in specialised literature.Variance analysis was used in order to interpret the results.

Results
On average, throughout the entire studied period, the main climate elements show a draughtier situation than the multiannual average: the annual average air temperature increased to 11.1 °C vs. 10.2 °C; air humidity decreased to 75% vs. 78%, sunshine increased to 2,159.5 vs. 2,097.1 hours, while annual rainfall was very close to the multiannual average of 622.7 mm vs. 613.7 mm.

Pedological drought in non-irrigated autumn cabbage crops
Pedological drought is defined as the total number of days with soil water reserve below the easily available water content on watering depth (0-50 cm).The analysis of the annual graphs of soil water reserve showed the presence of the pedological drought every year under study  in August (27 days) and September (23 days).In July, the frequency of the phenomenon was of 82% (21 days) and in June of 50% (8 days).The total number of days with pedological drought had an average value of 80 days, with a variation range of 8-112 days (Table 4).
There was a direct connection, very significant statistically speaking, between the number of days with pedological drought and the yield gain determined by irrigation (y = -0.0113x2+ 1.4351x -5.1845; R 2 = 0.962) (Fig. 1c).

Optimal irrigation regime
In order to maintain the soil water reserve between the easily available water content and field capacity, an irrigation rate of 2,410 m 3 /ha, with a variation range between 1,330 -4,900 m 3 /ha was used for the entire study period (1990 -2016) (Table 5).The average monthly irrigation rate was of 1,114 m 3 /ha (variation range 500-2,100 m 3 /ha) in August, of 714 m 3 /ha (0-1,560 m 3 /ha) in July, of 312 m 3 /ha (0-880 m 3 /ha) in June and of 270 m 3 /ha (0-1,100 m 3 /ha) in September, with considerable variability among months.

The influence of irrigation on the microclimate of the autumn cabbage
The use of the irrigation led to important microclimate changes affecting the crop.
One approach of characterizing microclimate is based on the use of climate indicators.Climate indicators may use one element of the climate, like temperature (the Thornthwaite index) or rainfall (the Topor index), two elements of the climate, like temperature and rainfall (the Martonne aridity index), the Seleaninov index, the Teaci index etc.).On average, during the entire period studied, the microclimate the interval between June and September was characterized as "average wet" (ICD = 9.8) for the nonirrigated crop compared to "wet" for the irrigated one (ICD = 16.5).On average, a difference of 68%, with a variation range between 12-359, was recorded in August.The highest difference recorded was also in August (161%, variation range 10-1,666).In July, the difference was of 79%, variation range 9-270.In June, the difference of 40%, variation range 0-373 and in September, the difference was of 34%, variation range 0-359 (Table 6).
The direct relationships between the Domuţa climate index and the water consumption index (y = 27.017x1.0925 ; R 2 = 0.9636) and those between the Domuța climate index and the yield (y = 0.9586x 1.3916 ; R 2 = 0.8102) were quantified for the interval 2006-2016 (Fig. 2 a,b).

The influence of irrigation on water consumption
Throughout the growing season, daily water consumption increased for the irrigated autumn crop compared to the non-irrigated one (Fig. 3).The highest difference (29 m 3 /ha) was recorded in August.At the same time, irrigation resulted in a statistically better regression function when compared to the non-irrigated variant: y = -0.0123x 2 + 1.44x + 17.375; R² = 0.9273 vs. y = -0.0043x 2 + 0.4307x + 21.835; R² = 0.7941 Consequently, the total water consumption for the irrigated autumn cabbage increased by 70% for the whole time interval under study (5,180 m 3 /ha vs. 3,045 m 3 /ha).The variation range of the total water consumption was between 1,073-4,421 m 3 /ha for the non-irrigated autumn cabbage and of 4,375-6,200 m 3 /ha for the irrigated autumn cabbage (Table 7).
Irrigation represented the main source in supplying the total water consumption for the irrigated autumn cabbage (47%).The amount of rainfall recorded from plantation to harvesting represented 46%.The water used from soil water reserve represented 7%.The amount of water used from the soil reserve was of 656 m 3 /ha for the non-irrigated variant and of 380 m 3 /ha for the irrigated one (Fig. 4).The influence of irrigation on the yield of autumn cabbage Irrigation resulted in a statistically significant increased average yield of cabbage of 53,256 kg/ha when compared to 21,050 kg/ha, the yield of non-irrigated cabbage.Throughout the studied years, the differences registered were very significant, statistically speaking; the standard deviation of the irrigated yield (1,760 kg/ha) decreased by 76% compared to the non-irrigated yield of autumn cabbage.The variation range of the yield was 0 (during three years) -50,990 kg/ha for the non-irrigated autumn cabbage, while it was between 27,150-66,130 kg/ha for the irrigated one (Table 8).
The percentage of irrigated cabbage heads was of 98%, higher than that of the non-irrigated ones which was of 79%.Statistically, the difference (24%) was very significant under the study interval 1990-2016.The variation range of the percentage was of 0-90% for the non-irrigated cabbage heads and of 88-100% for the irrigated ones (Table 9).Water use efficiency Water efficiency indicators show the amount of yield (yield gain) obtained for 1 m 3 (mm) of water or the amount of water used to obtain 1 kg of yield (yield gain).The study used the first category of indicators.
On average, throughout the studied period, water use efficiency for the irrigated cabbage was 60% higher than for the non-irrigated one: 11.8 kg/m 3 (variation range 4.7-13.12kg/m 3 ) for the irrigated cabbage and 6.91 kg/m 3 (variation range 0-8.18 kg/m 3 ) for the non-irrigated one.Irrigation water use efficiency recorded an average value of 13.4 kg yield gain/m 3 (variation range 6.7-24.2kg/m 3 ) (Table 10).

Discussion
The paper lies on researches carried out during the period 1990-2016, on preluvo-soil within the Agricultural Research Station from Oradea.It highlights significant arguments regarding the necessity of irrigation as a basic technological element of the autumn cabbage.
The context of the research was that in which pedological drought (the decrease of the soil water reserve below the easily available water content on watering depth 0-50 cm) was present every year.The highest number of days with pedological drought was recorded yearly during August, 27 days.The highest frequency of the phenomenon (100%) was recorded in August and September.Reverse correlations between the pedological drought and the water consumption, as well as the cabbage yield and direct correlations between the pedological drought and the irrigated yield gain were determined, all of them significant.
The research came as a data to be added on to existing works that highlight the necessity of irrigation to maintain the soil water reserve between easily available water content and field capacity on a depth of 0-50 cm.Previous authors such as Seidel et al. (2017) highlighted the importance of irrigation in a complex system of horticultural measures as a key to obtain high yields.The deficit of irrigation as a component of sustainable crop growth method had effects in actual plant size and leaves area, head fresh weight size and total yield, as proven by Xu and Leskovar (2014).In order to achieve the goals set up by using irrigation, the average value of the irrigation rate was of 2,410 m 3 /ha, with a variation range between 1,330 and 4,660 m 3 /ha.
Using the Domuta index allowed the authors to have an original approach on the data interpretation and gave the opportunity to highlight the improved ratio between rainfall + air humidity/air temperature + sunshine duration.Consequently, the value of the Domuta climate index (ICD) increased by 68% (wet II vs. wet); the variation range of the difference between the irrigated and nonirrigated cabbage crops was of 12-359%.A statistically assured direct correlation between ICD and the water consumption, respectively the autumn cabbage yield was thus determined, also referring to previous posts about this were done by Domuţa et al. (2008).
Irrigation helped obtain an optimal daily water consumption of the autumn cabbage.The highest difference between the daily water consumption for the irrigated cabbage and the daily water consumption for the non-irrigated cabbage was recorded in August, 128%.As a consequence, total water consumption increased by 70%.At the same time, the modelling of the daily water consumption values showed a polynomial function, with a higher correlation coefficient for the irrigated crop compared to the non-irrigated one.A paper to support this claim was published by Domuța et al. (2015), underlined the effects of the water consumption increase in cabbage as opposed to Costa et al. (2007) who concluded that in the context of water shortages, deficit irrigation can have some positive effects.The issue of deficit irrigation was also looked into by Xu and Leskovar (2014).Another point of discussion is the use of irrigation in supplying the optimal  water consumption for the cabbage.On the average, throughout the studied period, the percentages of the optimal water consumption supply were: irrigation 47%, rainfall from planting to harvesting 46% and soil water reserve 7%; one of the papers that had a claim similar was published by Domuţa et al. (2008).
Irrigation led to a yield gain of 153%, 53,256 kg/ha vs. 21,050 kg/ha respectively.Throughout the studied years, irrigation led to a very significant yield gain, statistically speaking.In three years, the yield of the non-irrigated cabbage crop was insignificant, it also generated improved stability: 1,760 kg/ha vs. 7,200 kg/ha.The correlation between open field agriculture and it`s results were highlighted by Csok et al. (2007).
The study points out a very significant statistically increase of cabbage heads: 98% vs. 79%.Irrigation ensured a percentage of over 95% of cabbage heads to be marketable according to Smittle et al. (1994).The goal of modern horticulture in the end is to obtain as much end product as possible, with a high marketable potential.This is what irrigation ultimately abides us to, and the two reference papers, although 20 years some apart, reach the same conclusion, to highlight the importance of irrigation.Water use efficiency improved 11.8 vs. 6.91 kg/m 3 , with a very significant statistically meaning.Allen et al. (1998) came to lay the foundation for basic water use efficiency and crop evapotranspiration, thus providing the link between nonirrigated water use efficiency versus irrigated water use efficiency.

Conclusions
The yearly presence of the pedological drought, the positive influence of irrigation on microclimate and water consumption, the statistically very significant annual yield gain and all the correlations of the soil -water -plantatmosphere system, enhance the idea that irrigation is a pivotal element that impose to be used for the autumn cabbage crop within Crișurilor Plain, Romania, without whom the yield drops significantly.

Fig. 1 .
Fig. 1.Correlation of the pedological indexes in autumn cabbage crop

Table 1 .
Physical and hydro-physical properties of the preluvo-soil from research site, Oradea 583

Table 3 .
The average values of the chemical indexes of the irrigation water used in research site

Table 4 .
Analysis of the pedological drought (days) in non-irrigated cabbage crop

Table 5 .
The irrigation regime (m 3 /ha) used to maintain the soil water reserve between the easily available water contend and field capacity in autumn cabbage crop

Table 6 .
The influence of irrigation on the microclimate (Domuța climate index, ICD) of the autumn cabbage crop

Table 7 .
Total water consumption and the supplying water sources for the non-irrigated and irrigated autumn cabbage crops

Table 8 .
The influence of irrigation on the yield of non-irrigated and irrigated autumn cabbage crops,Oradea, 1990Oradea,  -2016

Table 9 .
The influence of irrigation on the percentage of cabbage heads

Table 10 .
Water use efficiency (WUE) and irrigation water use efficiency (IWUE) in autumn cabbage crops