Winter barley performance on two different soils under conservation tillage systems

Abstract

Conservation tillage is becoming increasingly attractive to farmers due its potential to reduce production costs and allow a more sustainable land use as compared with conventional tillage. Field experiments were conducted over three consecutive growing seasons to study barley performance under three tillage systems (minimum, reduced, and conventional tillage) on two different soils (a sandy loam and a clay soil) of northern Greece. No significant differences in plant number, ear number, or grain yield were observed among tillage systems in any growing season in the sandy loam soil. By contrast, reduced plant number by 15 and 18% in the first growing season and by 18 and 21% in the third growing season was observed for the reduced and the minimum tillage system, respectively, in the clay soil as compared with conventional tillage. Reduced plant number in the clay soil was due to the unfavorable soil conditions during sowing and the uneven seedbed as a result of the presence of summer weeds which apparently prevented correct and uniform planting depth. However, no significant differences in ear number or barley grain yield were found among tillage systems in any growing season in the clay soil. Findings of this study showed that conservation tillage can affect the establishment of barley stands depending on soil type and weather conditions but this is not always expressed in grain-yield reduction due to the effect of compensation through increased tillering.

Keywords:

• Clay soil
• minimum tillage
• reduced tillage
• sandy loam soil

Introduction

Conservation tillage provides an interesting alternative to conventional tillage with major benefits for both the farmers and the environment (Uri et al., 1999; Lal et al., 2007). Adequate implementation of conservation tillage increases water availability for crops by increasing infiltration of water into the soil, reducing soil-water evaporation, and allowing better growth of root system by preventing or minimizing soil compaction. In addition, significant savings in fuel, labor, and machinery costs are realized with conservation tillage mainly by the fewer trips in the field during seedbed preparation (Lithourgidis et al., 2005, 2006b).

Although conservation tillage has been shown to ameliorate soil properties and also save time and energy, different and contradictory results often have been obtained when cereal growth and yields were compared under conventional and conservation tillage systems in dryland areas. Thus, although some studies found no significant differences in cereal production between conventional and various types of conservation tillage systems (Lithourgidis et al., 2005, 2006b; Moret et al., 2007), other studies reported lower grain yields under conservation tillage (López & Arrúe, 1997; Camara et al., 2003; Machado et al., 2007), whereas some others documented better crop yields under conservation tillage mainly due to greater soil-water storage and increased water-use efficiencies (Mrabet, 2000; McMaster et al., 2002; Hemmat & Eskandari, 2004). This variability in terms of grain yield is a major obstacle for farmers when deciding whether they will change to conservation tillage practices.

It is obvious from the above that no single tillage system is always appropriate for all situations as yields can be often affected by soil and climatic conditions, special local conditions, and sometimes by inadequate machinery and inexperienced farmers. In general, conservation tillage performs best in well- to moderately well-drained soils in arid and semiarid climates, and worst in heavy poorly drained soils in sub-humid and humid regions where traditional inversion systems are more suitable (Lal et al., 2007). Moreover, conservation tillage planting may cause special demands related to uneven seedbeds due to previous crop residues and the presence of weeds which often prevent correct and uniform planting depth. This may result in poor seedling emergence, thin stands, slow vegetative growth, and consequently reduced grain yield (Wilkins et al., 1989).

Conservation tillage in Greece has been practised thus far only on a limited scale by a minority of farmers and mostly empirically (Lithourgidis et al., 2009). Therefore, the available knowledge on the response of cereal crops to various types of conservation tillage as alternative tillage systems in Greece is limited and more data are required for the adoption of reduced tillage practices on a wide scale basis. As regards the use of conservation tillage on an experimental level, there are some encouraging data which indicated satisfactory crop establishment and considerable reduction in production costs with these systems compared with traditional tillage (Gemtos et al., 1998; Sidiras et al., 2000; Lithourgidis et al., 2005, 2006b; Dhima et al., 2006).

Reduction of production costs through reduced tillage is of particular importance for cereals growers in Greece where cereals are mainly grown in dry land and the produced grain yield is much lower than that obtained in other areas with longer growing seasons. However, as reported above, any conservation tillage practices should be tested for their suitability before their adoption in any particular region. Thus, the objective of this research was to study barley performance under different conservation tillage systems (conventional, reduced, and minimum) on two soils of northern Greece.

Materials and methods

A field experiment was conducted and repeated during 2003–2004, 2004–2005, and 2005–2006 at two sites of the rural area of the Prefecture of Pieria (located at 40^o09′02.64″N, 22^o13′38.80″E and 40^o14′07.59″N, 22^o29′22.60″E) in northern Greece. The two sites are at a distance of about 25 km apart. Some characteristic properties of the soil of each experimental field, determined at the initiation of the experiments, are shown in Table I. Total monthly rainfall recorded near the experimental areas for each growing season is presented in Table II. Cropping history at the experimental sites in the previous five years comprised a winter wheat crop under conventional tillage.

Table I. Selected physicochemical characteristics of the two soils at the initiation of the experiment (0–30 cm depth).

	Site 1	Site 2
Sand, g kg^−1	542	278
Silt, g kg^−1	279	301
Clay, g kg^−1	179	421
Texture	Sandy loam	Clay
pH (1:2 H2O)	6.8	7.2
ECse, dS m^−1	0.49	2.29
CaCO3, g kg^−1	49.2	84.2
Organic matter, g kg^−1	9.7	17.2
Total soil nitrogen, mg kg^−1	720	1660

Table II. Monthly rainfall (mm) recorded near the experimental areas during the growing seasons.

	Site 1			Site 2
	2003–2004	2004–2005	2005–2006	2003–2004	2004–2005	2005–2006
	Fallow season
June	4	4	9	8	2	15
July	42	8	20	50	10	29
August	37	12	28	47	24	24
September	21	8	25	19	14	29
October	47	16	40	86	15	35
Season	151	48	122	210	65	132
	Cropping season
November	45	23	42	68	27	69
December	64	65	38	91	74	55
January	38	39	23	36	34	32
February	10	16	98	2	29	136
March	29	17	48	24	25	56
April	49	10	35	54	2	40
May	45	13	22	45	17	29
Season	280	183	306	320	208	417

Sowing took place about mid-November, which is the optimal time for barley sowing in northern Greece. Barley var. ‘Thermi’ was sown in rows (spaced 16 cm apart) at a seeding rate of 150 kg h⁻¹. Nitrogen (N) at 80 kg⁻¹ and P₂O₅ at 40 kg ha⁻¹ applied as ammonium sulfophosphate (20-10-0) were applied in the soil two days before any tillage treatments each year. In addition, 30 kg N ha⁻¹ as ammonium nitrate (33.5-0-0) was applied surface broadcast in all plots in early March. The fertilization rates used are the common rates for barley production in the area. Weed control was achieved with postemergence application of diclofop-methyl at 560 g ai (active ingredient) ha⁻¹ and tribenuron at 7.5 g ai ha⁻¹. No irrigation was applied in any growing season. In addition, a week before barley planting, paraquat at 0.4 kg ai ha⁻¹ was applied in minimum tillage plots to control weeds.

The experiments were arranged in a randomized complete-block design with three treatments (tillage systems) replicated four times. Plot size was 12 by 20 m, which allowed the use of commercial-size farm equipment for cultural operations. The three tillage systems were: (i) MT (minimum tillage), where barley sowing was made after shallow tillage with cultivator to a depth of 10–12 cm (operation speed of 8 km/h), (ii) RT (reduced tillage), where barley was sown after tillage with heavy offset harrow disc to a depth of 16–18 cm and followed by cultivator to a depth of 10–12 cm (respective operation speed 10 and 8 km/h), and (iii) CT (conventional tillage), where barley was sown after tillage with a four-bottom mouldboard plough to a depth of 20–22 cm (speed of 7 km/h), followed by a tandem harrow disc to a depth of 10–12 cm (speed of 11 km/h), and by cultivator to a depth of 10–12 cm (speed of 8 km/h); the latter is the common tillage practice for barley production in Greece and was considered as control. A 75 HP (55 kW) Massey-Ferguson tractor (Model MF375) was used for all operations. In all plots, barley was planted with farmer's equipment (8-row sowing machine, John Deere 7000). The planter was equipped with a disc opener (30-cm diameter) and was adjusted to plant at a depth of 3 to 4 cm in rows 16 cm apart, at a planting speed of 5–6 km/h.

Plant number, ear number, and grain yield of barley were determined for all plots in each year. Barley plants were counted 6 weeks after planting in two random areas of 1 m² each in all plots. At harvest, plants from the same areas were selected to determine ear number. Barley was harvested in the second half of June of each growing season and grain yield was adjusted to 130 g kg⁻¹ grain moisture. Grain yield was determined by harvesting a 4.5 by 15 m area of each plot with an appropriate grain-harvesting machine. Barley straw was baled and removed after harvest.

The experiments were located in the same areas each year and were repeated in the second and the third growing season following exactly the same procedure using the same tractor and machinery. Data were subjected to analysis of variance (ANOVA) separately for each location using a three by three factorial approach (three growing seasons by three tillage treatments). Owing to significant differences among years and between year and treatment interaction, means are presented separately for each year. Differences between treatment means were examined by the protected least significant difference (LSD) test at the 0.05 probability level.

Results and discussion

No significant differences among tillage systems were observed in plant number, ear number, and grain yield of barley in the sandy loam soil in any growing season (Table III). However, ear number and grain yield were affected by growing season with lower values recorded in the dry growing season (2004–2005) as compared with the other two growing seasons. The lower values in 2004–2005 were apparently due to the lower total rainfall during that growing season and particularly to the lower spring rainfall (March to May). Rainfall is an important factor for cereal growth and yield in soils with low water-holding capacity (Sadras & Roget, 2004) where significant yield variation has been reported with the amount of rainfall and particularly with the amount of spring rainfall (Lithourgidis et al., 2006a). Sandy loam soils normally dry out rapidly due to their low water-holding capacity, permanent wilting point, and available water and therefore these soils depend much on rainfall mainly during the critical periods of cereal growth (Lithourgidis et al., 2006a). Similar results, as regards wheat establishment, were reported by Lafond et al. (1992) who found that wheat populations did not differ among conventional, reduced, or no-tillage systems in a 4-yr study in Saskatchewan and Carr et al. (2003) who found that wheat stand was not affected by tillage systems. As regards barley yield under conservation tillage, several studies showed no detrimental effect of conservation tillage on yield, reporting barley yields comparable or even superior to those obtained under conventional tillage (Malhi et al., 1992; Lampurlanés et al., 2001; Cantero-Martínez et al., 2003; Moret et al., 2007). Similarly, data of the present study indicated that reduced or minimum tillage systems seem to be a viable alternative to traditional tillage for barley production in sandy loam soils without any effect on barley performance and thus these systems are desirable for barley production due to the reduced costs realized in terms of labor and fuel consumption.

Table III. Number of barley plants (no. m⁻²), ears (no. m⁻²), and grain yield (kg ha⁻¹) as affected by growing season and tillage system in the sandy loam soil (Site 1). (Different letters within each variable indicate statistically significant differences at P=0.05.)

	Conventional tillage		Reduced tillage		Minimum tillage
	Plant number (no. m^−2)
2003–2004	227	a	233	a	225	a
2004–2005	219	a	221	a	216	a
2005–2006	225	a	232	a	226	a
	Ear number (no. m^−2)
2003–2004	411	a	424	a	412	a
2004–2005	310	b	337	b	331	b
2005–2006	405	a	420	a	413	a
	Grain yield (kg ha^−1)
2003–2004	2240	a	2190	a	2210	a
2004–2005	1730	b	1800	b	1790	b
2005–2006	2130	a	2180	a	2140	a

By contrast, reduced plant number by 15 and 18% in the first growing season and by 18 and 21% in the third growing season were observed for reduced and minimum tillage system, respectively, in the clay soil compared with conventional tillage (Table IV). Reduced plant number in the clay soil occurred when a wet period preceded planting, resulting in high soil moisture during planting (Tables II and IV) and also in increased populations of summer weeds. Thus, the lower barley populations under conservation tillage could be attributed to the unfavorable soil conditions during sowing (high soil moisture) and also to the uneven seedbed due to the presence of summer weeds which apparently prevented correct and uniform planting depth. Moist soils, covered with plant residues, dominate during late fall when sowing is performed. Although this provides an ideal environment for seed germination, such conditions can prevent planters from cutting through residue, penetrating the soil to the proper planting depth, and establishing good seed-to-soil contact (Kumar & Goh, 2000). Moreover, soil moisture accumulation in the untilled fallow encourages the rapid development of weeds and in the absence of crop weeds have practically unlimited resources for growth and development with minimal competition. The application of paraquat before barley planting only partially overcame the problem, which means that additional herbicide applications or perhaps the use of other herbicides may be required during the fallow period. Alternatively, shallow soil tillage (e.g., tandem harrow or cultivator) early in the fallow period after the emergence of most summer weeds could be considered as a weed-control method to prevent the rapid growth of summer weeds. Such problems are avoided under conventional tillage because in this case the seedbeds are finely worked and the seeds are uniformly planted into the bare ground. Lower plant population under ridge tillage than with conventional tillage was previously reported for barley (Borin & Sartori, 1995). Similarly, fewer plants under no-tillage than with traditional tillage were previously reported for winter wheat (Wilkins et al., 1989; Lithourgidis & Tsatsarelis, 2002). On the other hand, Sidiras et al. (2000) reported better barley seedling emergence in no-tillage plots than in rotary hoed (minimum tillage) and ploughed (conventional tillage) treatments.

Table IV. Number of barley plants (no. m⁻²), ears (no. m⁻²), and grain yield (kg ha⁻¹) as affected by growing season and tillage system in the clay soil (Site 2). (Different letters within each variable indicate statistically significant differences at P=0.05.)

	Conventional tillage		Reduced tillage		Minimum tillage
	Plant number (no. m^−2)
2003–2004	244	a	207	de	200	ef
2004–2005	230	abc	219	cd	223	bcd
2005–2006	239	ab	195	ef	188	f
	Ear number (no. m^−2)
2003–2004	456	ab	445	abcd	433	abcd
2004–2005	387	cd	391	bcd	382	d
2005–2006	461	a	450	abc	437	abcd
	Grain yield (kg ha^−1)
2003–2004	3580	a	3550	a	3530	ab
2004–2005	3110	c	3210	bc	3140	c
2005–2006	3730	a	3640	a	3580	a

Despite the reduced number of barley plants in the clay soil, there were no significant differences in ear number and grain yield among tillage systems in any growing season in the clay soil (Table IV). This was apparently due to the increased tillering which took place to offset the reduced stand density of plants grown under minimum or reduced tillage. In particular, the initial differences by 15% (244 vs. 207 plants m⁻²) and 18% (244 vs. 200 plants m⁻²) between conventional tillage and reduced or minimum tillage, respectively, in the first growing season decreased to 2% (456 vs. 445 ears m⁻¹) and 5% (456 vs. 433 ears m⁻¹) in ear number. The same was also observed in the third growing season where the initial differences in barley plant number between the conventional tillage and the reduced or the minimum tillage were reduced considerably in ear number. This means that barley plants compensated for the low population densities through increased production and survival of tillers. Barley has been reported to overcome poor plant density through increased tillering under ridge tillage, supplying the same number of fertile tillers as in conventional tillage (Borin & Sartori, 1995). This compensating effect for low population densities through increased tillering is common in cereals (Whaley et al., 2000; Gooding et al., 2002; Lloveras et al., 2004; Lithourgidis et al., 2006b) and it may partially or totally overcome differences in plant number after crop establishment, thus allowing crop recovery from possible early damage.

Findings of this study showed that conservation tillage can be a viable alternative for barley production, allowing the implementation of more sustainable cropping systems. However, under certain conditions it is possible that conservation tillage may influence the establishment of barley stands depending on soil type and weather conditions. While barley establishment and yield were not affected by conservation tillage practices in the sandy loam soil, reduced plant number was observed under these practices in the clay soil. In particular, in heavy and poorly drained soils the planting equipment may not be totally successful with respect to uniform and correct seed placement in a wet and uneven seedbed. In this case, reduced plant populations may occur under conservation tillage practices in heavy soils after wet fallow periods. However, differences in plant number among tillage treatments are not always expressed in grain-yield reduction, due to the effect of compensation through increased tillering. In any case, environmental conditions of each specific site must be taken into account when selecting and applying various types of conservation tillage systems to optimize expected results.