The hydric stress influence on quantity and quality of the maize yield in the Crisurilor Plain conditions

Station Oradea, Crisurilor Plain during 2008–2011in the following variants: V1=Irrigated, without irrigation suspending; V2=Irrigated, irrigation suspending in May; V3=Irrigated, irrigation suspending in June; V4=Irrigated, irrigation suspending in July; V5=Irrigated, irrigation suspending in August; V6=Unirrigated. The hybrid used: Fundulea 376. In the variant with optimum irrigation, water reserve on


INTRODUCTION
The Crişurilor Plain occupies the central part of the Western Plain of Romania and maize and wheat are cropped on the biggest surfaces (Borza, 2006(Borza, , 2007)).The first researches from this area regarding the maize irrigation were started on the chernozem from Girişu de Criş in 1967 by Stepănescu and Mihăilescu.(Domuţa, 2010(Domuţa, , 2011)).
The researches regarding the irrigation participation in the total water consumtion from in the Crişurilor Plain were carried out during 1976-2010 on the preluvosoil from Oradea in the research field from soil water balance study.(Domuţa, 2009b).The results researches emphasized the need of the irrigation in the optimum water consumption, the increase of the water consumption and yields gains very significant statistically in irrigated variant vs. unirrigated variant.Most of the years, the water use efficiency improved using the irrigation.(Domuţa, 1995(Domuţa, , 2009a;;Grumeza and Kleps, 2005).The researches from the other areas emphasize the positive influence of the irrigation on water use efficiency (Borza, 2008(Borza, , 2009;;Nagy, 2010;Pakurar et al., 2010;Stan and Năescu, 1997).
Irrigation suspending in different months of the vegetation period determines the yield losses and the smaller water use efficiency (Borza, 2007).
The following variants were studied: V 1 =Unirrigated; V 2 =Irrigated without the irrigation suspending in the maize irrigation season; V 3 =Irrigated, with irrigation suspending in May, 4-9 leaves; V 4 =Irrigated, with irrigation suspending in June, 10-18 leaves; V 5 = Irrigated, with irrigation suspending in July, tassel growth -grains filling; V 6 =Irrigated, with irrigation suspending in August, grains filling-ripening.The surface of the experiment plot was 50 m 2 .Number of repetition=4; Irrigation method used was sprinkler with modifications for rectangular plots.Cultivar used: Fundulea 376.Fertilization system: N 120 P 90 K 60 .
Soil moisture of 0-75 cm depth was determined ten to ten days.In the variant without irrigation suspending the moment of the irrigation use was when the soil water reserve on 0-75 cm depth decreased to easily available water content.In the variant with irrigation suspending in different months didn't irrigate in these months.
De Martonne aridity index (IdM) was used for climate characterization: climate indicator was use: In wich: P = rainfall (and irrigation) (mm), t = month average temperature ( o C).Water consumption was determined using the soil water balance method and water use efficiency was determined like report between field and water consumption (Brejea, 2009).
The protein content of the maize grains was established using the total nitrogen content by formula: total N × 6.25.Total nitrogen was determined by Kjeldahl method.
Results research was processed by variance analysis and with the regression functions (Domuţa, 2006).

Climate elements
The researches were carried out in the specifical climate conditions: annual average temperature over the multiannual average, rainfall and air humidity smaller than multiannual average in 2008,2009,2011 and over the multiannual average in 2010 (table 1).

Pedological drought
In the year 2008, in unirrigated maize, the soil water reserve on 0-75 cm decreased bellow easily available water content 81 days: 6 days in May, 20 days in June, 24 days in July, 31 days in August; soil water reserve decreased bellow wilting point 7 days (4 days in July and 3 days in August).Pedological drought was registered in the variants with irrigation suspending in the month without irrigation (table 2).
The biggest number with pedological drought was registered in 2009, 108 day.Pedological drought started in April (3 days) and it was determined all the days of the month May, July and August; in June pedologiccal drought was determined in 12 days (table 2).Strong pedological drought was determined in 32 days: 9 daysin June, 10 days in July and 13 days in August (table 3).
The smallest number of days with pedological drought ( 20 days:10 days in July and 10 days in August) was registered in 2010.Strong pedological drought didn't determined in 2010.
In 2011, pedological drought started in April (7 days); it was determined all the days of the May and june and was determined in 10 days in July and in 15 days in August.Strong pedological drought was determined in 20 days: 6 days in June, 4 days in July and 10 days in August.
There is an inverse link between the number of days with pedological drought and the maize yield level (figure 1).The same type of link was quantified between number of days with pedological drought and yield gains obtained using the irrigation.

Climate drought
The most known climate indicator from Romania is de Martonne aridity index and this indicator was used for characterization of the microclimate created by irrigation using (Domuţa, 2012).
Maintaining the soil water reserve between easily available water content and field capacity determined to use the following irrigation rate: 3320 m 3 ha -1 in 2008, 4200 m 3 ha -1 in 2009, 500 m 3 ha -1 in 2010, 3500 m 3 ha -1 in 2011.In the variant with irrigation suspending, the values of the irrigation rates were smaller.Irrigation rates had the specifical values for every year (table 4).

Agricultural year
October November December January February March April May June July August September Average/ Total Average air temperature (°C) 2 0 0 8 1 0 .3 3 .7 -0 .4 1 .4 3 .4 6 .5 1 1 .6 1 6 .9 2 1 .0 2 0 .9 2 2 .0  The irrigation use determined bigger values of the water/temperature report calculated by de Martonne aridity index.In average on the studied period the differences were of 57.9% in Aprilie, of 78.6% in May, of 83.9% in June, of 110.3% in July and of 111.5% in August.The period Aprilie-August in unirrigated maize was characterizated like "demiarid" in 2008, 2009 and 2011 and like "moderate wet II" in 2010.The irrigation determined a microclimate characterized like "wet" all the year study.The diffrences between the values of the de Martonne aridity index calculated for variant with optimum irrigation and the values of the de Martonne aridity index in unirrigated maize were of 117% in 2008, of 157% in 2009, of 11% in 2010 and of 140% in 2011 (table 5).
A direct link were quantified between the values of he de Martonne aridity index and maize yield.The same type of link was registered between the values of the de Martonne aridity index and yield gains determined by irrigation (figure 2-3).

Hydric stress influence on maize water consumption
Regression functions for daily water consumption of the maize from studied variants were calculated and the smallest correlation coefficient was registered in unirrigated variant (R 2 =0.6327) and the biggest correlation coefficient (R 2 =0.8761) was registered in the variant without irrigation suspending.In the variant with irrigation suspending, the correlation coefficients values was smaller than in the variant without irrigation suspending (figure 4).
In average on the studied period, in the variant without irrigation suspending was registered a maize total water consumption of 7142 m 3 ha -1 , with 59% bigger than the total water consumption (4501 m 3 ha -1 ) of the unirrigated variant.In the variant with irrigation suspending, the values of the total water consumption were smaller than the values registered in the variant without irrigation suspending (table 6).all the years studied; in average on the studied period, the protein content of the maize grains was of 11.29%.
In the variants with irrigation suspending the protein content decreased significant statistically (-6%) in the variant with irrigation suspending in May, distinguee significant (-15% by irrigation suspending in June), very significant statistically (-24% and -29% by irrigation suspending in July or August).The smallest protein content of the maize grains was registered in the unirrigated variant (-41%) (table 8).The relative differences of the gross protein quantity in comparison with the variant without irrigation suspending had bigger values, the relative differences registered regarding the yield were of: -15% in the variant with irrigation suspending in May, -36% in the variant with irrigation suspending in June, -45% in the variant with irrigation suspending in July, -47% in the variant with irrigation suspending in August and -74% in unirrigated maize.

Hydric stress influence on yield level
In average on the studied period, the biggest value of the yield, 12473 kg ha -1 was registered in the variant with optimum regime of soil water reserve on watering depth (0-75 cm).The irrigation suspending determined the yield losses of 28% in the variant with irrigation suspending in July, the yield losses of 25% in the variants with irrigation suspending in June or August and yield losses of 10% in the variant with irrigation suspending in May; all the yield losses are very significant statistically.The biggest yield loss, 53%, was determined in unirrigated maize (table 7).

Hydric stress influence on protein content of the maize grains
The biggest protein content of the maize grains were determined in the variant without irrigation suspending

CONCLUSIONS
The researches regarding the irrigation suspending in the vegetation period of the maize were carried out during 2008-2011in Agricultural Research and Development Station Oradea and a following conclusions there were: -Pedologial drought was determined every year in unirrigated variant; in the month with irrigation suspending, the pedological drought was determined, too.Strong pedological drought was determined in 7 days in 2008, in 32 days in 2009, and in 20 days in 2011; strong pedoogical drought didn't registered in 2010, the year with rainfall more than multianual average.
-Maintaining of the soil water reserve between easily available water content and field capacity determined to use an irrigation rate of 3320 m 3 ha -1 in 2008, of 4200 m 3 ha -1 in 2009, of 500 m 3 ha -1 in 2010 and of 3500 m 3 ha -1 in 2011; -The differences between the values of the de Martonne aridity index from optimum irrigated variant and unirrigated variant were of 117% in 2008, of 157% in 2009, of 11% in 2010 and of 140% in 2011; -The irrigation determined the increase of the daily water consumption.As consequence, the maize total water consumption in the variant with optimum irrigation increased with 59%.The total water Note: lSD 5% = 0.59, lSD 1% = 1.15, lSD 0.1% = 1.96 consumption values decreased in the variants with irrigation suspending; -The average of the yield maize obtained in the variant without irrigation suspending was of 12 473 kg ha -1 .The irrigation suspending determined the yield losses very significant statistically.The biggest yield loss was registered in unirrigated variant, -53%; -There were the bigger value of the grain protein content in the variants without irrigation suspending.In the unirrrigated variant and in the variant with irrigation suspending the protein content of the maize grain are smaller; the differences are statistically assured.
-The inverse links, statistically assured, were registered between the number of days with pedological drought and yield level and protein content of the yield maize, respectivelly; -The direct links were quantified between the water/ temperature report (de Martonne aridity index) and yield level and protein content of the maize grains.The links are statistically assured.
The researches sustain the irrigation like the main measure for drought control in the Crişurilor Plain.

Figure 1 :
Figure 1: Correlation between the number of days with pedological drought (WR-Wea) and maize yields (Oradea, 2008-2011) Figure 2: Correlation between the values of the de Martonne aridity index (IdM) and yields in maize crop (Oradea, 2008-2011) during the irrigation season of the maize by de Martonne aridity index (r a c t e r i z a t i o n M o d e r a t e w e t I