CONSERVATION OF SOIL MOISTURE IN DEEP TILLAGE RIGOSOL UNDER WHEAT AND MAIZE

Abstract: At the experimental field “Radmilovac” of the Faculty of Agriculture of the University of Belgrade the study of the conservation of soil moisture in deep tillage Rigosol was carried out. The so called type of soil Rigosol was covered by wheat and maize. The Rigosol was formed by special treatment of the parent soil the Eutric Cambisol. The researches have been conducted during the most important phenophases of the crop growth, including formation of kernels, flowering, fertilization, grain filling and maturity. Special attention was paid to the measurements of soil moisture in the period when crop water requirements are the greatest. The conservation of the soil moisture was observed along the vertical profiles of soil. The following parameters were monitored: time intervals without rainfall, precipitation rate and the rate of crop phenophase development. Very favourable soil moisture conservation was observed, both for wheat and maize covered soil. The greatest content of soil moisture was measured at the depths from 10 to 30 cm, in the zone of crop roots. As the consequence, the favourable conditions for crop growth and yields were observed. Deep tillage of soil had positive effects on homogeneous distribution of soil moisture along the vertical profile, independently of the crop type. It was shown that the Rigosol ensures better conservation of the soil moisture than the parent soil (Eutric Cambisol), if all agriculture measures are applied in the proper time.


I n t r o d u c t i o n
In agriculture soil represents the basis of plant production.Apart from water and mineral matter, it is an essential resource that human existence depends on.Therefore, studying soil production capacity and finding the way how to increase it are the most important tasks of contemporary science and practice.The highest increase in soil production capacity i.e. its fertility can be mainly achieved by regulating its water regime, which is done by means of various cultural practices and ameliorative measures.
The aim of the study was to find out the level of Rigosol soil moisture conservation after rainfall, in deep tillage, when diverse arable crops are grown.
K o v a č e v i ć (2003), J e v t i ć (1992) and K o n s t a n t i n o v i ć (1992) reported that best accumulation and conservation of soil moisture is achieved by deep tillage at the depths from 25 to 35 cm.
According to K o n s t a n t i n o v i ć (1992) and S p a l e v i ć (1994), the outcomes of soil erosion process are largely dependent of moisture conservation at the moment of precipitation i.e. rainfall occurrence.Moisture conservation is determined to a large extent by some soil physical properties (S p a l e v i ć , 1995).
M o l n a r et al. (1981) point out that it is necessary to provide maintenance of soil fertility by selecting appropriate tillage, so as to ensure high and steady yields of grown crops.
In studying the effects of tillage depth and fertilization on maize yield, D r e z g i ć et al. (1972) pointed out the superiority of deep tillage over disking, especially in dry years.
T o d o r o v i ć and B o ž i ć (1995) as well as A d a m (1981) stress that in heavier soil types deep tillage has ameliorative function and contributes to forming new anthropogenic soils.

Material and Methods
The study was conducted on the "Radmilovac" Experimental Field of the Faculty of Agriculture -Zemun, in deep tillage conditions of Rigosol formed by special treatment of the parent soil the Eutric Cambisol.
To determine soil moisture level after rainfall, two experimental plots 17 m x 70 m in size (approx.12 ares) were used, located on the northeastern slope of the Experimental Field.Wheat variety "Kraljevica" was grown on one plot, where sowing density was 600 -650 plants per m2, while maize hybrid ZP SC 539 was grown on another plot with approx.57,142 plants/ha (70 cm x 25 cm).
Prior to wheat and maize sowing, deep tillage was done at the depth of 25 cm.Sunflower was a preceding crop in wheat, while red clover was in maize.
On each experimental plot one soil profile was opened.In doing this, care was taken that profiles were in almost identical conditions of soil forming process i.e. that they had similar relief elements.
From opened, previously morphologically studied profiles in detail, soil was continually sampled for analysis in disturbed condition from 0-10, 10-20, 20-30, 30-40 and 40-50cm depth.Also, from identical depth zones soil was sampled for analysis in undisturbed condition in three replications each with Kopecki cylinders of 100 m3 vol.
Apart from opening the profiles, field studies comprised measurements of water infiltration rate and Rigosol infiltration capacity by using metal cylindrical infiltrometers.
Moisture distribution after rainfalls was monitored per phenophase or plant growth stage by collecting soil samples with a sampling rod from the said depths.Phenophases monitored in wheat were: heading, flowering, kernel formation, grain filling, milk stage, maturity, waxy ripeness, and in maize: tasseling, flowering, kernel formation, grain filling, milk stage, maturity, waxy ripeness.
Samples in disturbed and undisturbed state were subjected to laboratory analyses in order to determine soil physical properties (mechanical and aggregate structure, textural classes, specific mass and bulk density, total porosity, maximum water holding capacity, moisture retention under various pressures, air capacity, hygroscopic moisture, current moisture content and filtration coefficient, using the device with steady pressure), agrochemical properties (CaCO 3 content, pH value in H 2 O and 1N KCl, humus and total N content, organic C content, available P and K content, total Al and Fe content), and Rigosol mineralogical structure by x-ray diffraction analysis.Soil physical and chemical properties were analyzed according to internationally recognized methods as well as those determined by Yugoslav Soil Science Society (Handbook for Soil Testing, Book 1: -Chemical Methods of Soil Testing, 1966; Book 5: -Methods of Soil Physical Properties Testing, 1971 and Methods of Investigating and Determining Soil Physical Properties, 1997).

Rigosol mineral structure
Mineralogical analysis evidenced similar mineral structure of Rigosol along vertical profiles on experimental plots under wheat and maize.Clay minerals are in highest proportion.The analysis of clay fraction showed that it is made up of illite, smectite, kaolinite, chlorite, mixed-layer clay minerals and traces of quartz.

Rigosol mechanical and aggregate structure
According to American classification of soil textural classes, the studied Rigosol under wheat and maize belongs to loams containing fractions of clay (particles smaller than 0.002 mm) from 21.7 -26.8%.The proportion of silt fraction (particles from 0.02 -0.002 in diameter) is from 31.5 -35.9%, whereas total sand particles (particles from 2 -0.02 mm in diameter) are within the 37.0 -44.2% range.

Rigosol aggregate structure and stability
The results of comparative studies did not indicate any significant differences in the structure of Rigosol under wheat and maize.The proportion of the most favorable structural aggregates in terms of agronomy (0.25 -10 mm), in a halfmeter layer (0 -50 cm) varies from approx.65 -74%.
Also, data on waterproof of structural aggregates indicate no significant differences between the studied Rigosol under wheat and that under maize.The content of waterproof aggregates larger than 0.25 mm varies from 41.3 -57.2%.

Basic physical and air properties of Rigosol
The results observed for basic Rigosol physical (bulk density and specific mass) and air properties (total porosity and air capacity) do not demonstrate any significant differences between plot under wheat and that under maize.Values for bulk density vary from 1.30 -1.46 g/cm3 and for specific mass from 2.70 -2.75 g/cm3.Total porosity ranged from 46.9 -51.9%.On both plots air capacity was low, based on Pelišek (Ž i v k o v i ć , 1991) classification, varying from 5.43 -9.40%.

Rigosol water-physical properties
Soil water properties were characterized by data on maximum water holding capacity (MWHC) and moisture retention capacity (MRC), lento capillary moisture (LCM), plant permanent wilting moisture (PWM), available water capacity for plants (AWC), and filtration coefficient.
According to moisture retention capacity level, the studied Rigosol belongs to a soil class of medium-retention capacity, as classified by A s t a p o v a (1958).P e j k o v i ć (1972) reported similar results for the levels of mentioned water capacities.
In the studied Rigosol, values of filtration coefficient along vertical profiles vary from 7.3 x 10 -4 to 1.8 x 10 -4 cm/s.According to the Benedixen classification (R u d i ć , 1983), those values are characteristic of medium poorly permeable soils.

Rigosol agrochemical properties
Additional studies were conducted to better and more easily explain and comment moisture conservation in Rigosol.Therefore, the most significant chemical properties of Rigosol were analyzed, attention being focused on the pHvalue, content of humus, CaCO 3 , N, P 2 O 5 , K 2 O, Fe and Al.
According to pH-values, the studied Rigosol belongs to the class of poorly alkaline soils (pH in H 2 O varies from 7.7 -8.2 and in nKCl from 7.2 -7.5), whereas according to CaCO 3 content (2.18 -8.37%), it falls into the group of moderate to medium calcareous soils.Humus content varies from 1.18 to 1.36%, which is characteristic of poor humose soils.As for total N content (0.074 -0.088%), Rigosol belongs to medium supplied soils.It is well supplied with available phosphorus (P 2 O 5 ranges from 45 -85 mg/100 g soil) and available potassium (K 2 O ranges from 20.1 -34.2 mg/100 g soil).Total Fe content varies from 3.00 -3.83%, while total Al content from 6.15 -8.80%.
Values of the said agrochemical parameters fall within the range expected for this soil type, considering that the studied Rigosol was formed from eroded Eutric Cambisol.

Moisture content in soil under wheat
The results of monitoring current moisture content in soil under wheat along vertical profiles from 0-50 cm are shown in Tab. 1 and Graph 3. Moisture depended of time interval between precipitation occurrence and time of sampling.It was found that in all cases there exists identical regularity: amount of precipitation -vertical profile -time of sampling.
Graph 1 shows data on infiltration properties of Rigosol under wheat according to its most important stages of growth.Values for infiltration rate in wheat are highest in the first hour, declining abruptly throughout the rest of time taken for measurements.According to classification cited by Kovda (JPDZ 1997), infiltration rate in Rigosol under wheat is satisfactory, however, there is danger of weak erosion.

Moisture content in soil under maize
Based on data from Tab. 2 and Graph 4, it is evident that there is similar regularity between moisture content in Rigosol under maize and that under wheat as well as between the amount of precipitation -vertical profile -time of sampling.--------- According to ameliorative assessment of water infiltration into soil, as described by the mentioned classification, infiltration rate in Rigosol under maize in the first hour of measurements is close to satisfactory and good, but there is also danger of weak erosion.

Characteristics of moisture conservation in deep tillage
Rigosol under wheat and maize Characteristics of moisture content in deep tillage Rigosol under wheat and maize were determined only by the amount of precipitation because deep underground water did not produce any effects.
To gain insight into the characteristics of moisture conservation, certain criteria for observing moisture level had to be set.
First, moisture level was observed along vertical profiles from 0-10cm; 10-20cm; 20-30cm; 30-40cm; 40-50cm in both wheat and maize, depending on the length of time interval without rainfall relative to date of sampling and method of soil utilization.
In wheat, time intervals without rainfall were one day, six, and seven days, but in a one-day variant four cases were analyzed, when up to 5 mm, 10 mm, 35 mm and 45 mm of rain fell.In a six-day variant two cases were subjected to analysis: in one case 33 mm of rain fell, while in another 33.10 mm.In a sevenday variant there was only one case with 53.40 mm of rainfall.
In maize, time intervals without rainfall were one day, two, six, and seven days.In a one-day variant four cases were considered, when up to 20 mm, 30 mm, 35 mm and 45 mm of rain fell.In other variants, one case was analyzed each, such as: in a two-day variant when 14.70 mm of rain fell, in a six-day variant when 7.60 mm of rain fell, and in a seven-day variant when 8.40 mm of rain fell.
Values for moisture conservation in wheat, in the first case of the first variant, when samples were collected one day after 4.10 mm rainfall, were as follows: 0-10cm 13.89%; 10-20cm 18.25%; 20-30cm 17.69%; 30-40cm 17.19%; 40-50cm 17.01%, which is explained by a small amount of rainfall the previous day and a large amount of rainfall (61.90mm) four days prior to the last rainfall that remained mainly at approx.20 cm depth.
In the fourth variant, when samples were collected seven days after a 8.40mm rainfall, values for moisture content were: 0-10cm 5.31%; 10-20cm 10.77%; 20-30cm 12.14%; 30-40cm 12.04%; 40-50cm 11.72%.Moisture content in a surface soil is considerably lower than in deeper layers, by over 50%, which is explained by a small amount of rainfall and relatively long dry period prior to rainfall.

C o n c l u s i o n
The results indicate that moisture conservation takes place mainly at the depth greater than 10 cm i.e. at the 10-30cm depth.In this zone, the largest part of the grown crops' root system is found.
During time periods without rainfall, not longer than seven days, there is sufficient conserved moisture so that the drought problem is overcome, which makes possible for plants to normally develop the next phenophase.
Soil tillage at the 25cm depth produced favorable effects on the water infiltration process, concerning both intensity of infiltration and infiltration capacity in wheat as well as in maize.
Infiltration rate also depended on the stage of growth of both wheat and maize, so that the highest intensity of infiltration rate under wheat was in the heading-flowering phenophase and that under maize in the kernel formation phenophase.