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Soil & Crop Management

Tillage System, Preceding Crop, and Nitrogen Fertilizer in Wheat Crop

II. Water Utilization

^a Dep. de Ciencias Agroforestales, Univ. of Huelva, Campus de La Rábida, 21819 Palos de la Frontera (Huelva), Spain
^b Dep. de Ciencias y Recursos Agrícolas y Forestales, Univ. of Córdoba, Córdoba, Spain
^c Dep. de Producción Vegetal y Tecnología Agraria, Univ. of Castilla-La Mancha, Spain

^* Corresponding author (rafael.lopez{at}dcaf.uhu.es)

Received for publication January 31, 2006.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Under rainfed Mediterranean conditions, where water constitutes the limiting factor, the aim is to obtain the highest production per unit of available water. A 6-yr study in a Vertisol was undertaken to determine in wheat (Triticum aestivum L.) the effects of tillage system, preceding crop, and N fertilizer on water utilization. Tillage treatments were no-tillage and conventional tillage. Preceding crops, in 2-yr rotations, were sunflower (Helianthus annuus L.), chickpea (Cicer arietinum L.), faba bean (Vicia faba L.), fallow, and continuous wheat. The mean crop precipitation interception index (CPI) was low (43%). Rotations including spring-planted crops such as chickpea and sunflower, or including fallow, reduced the CPI, increasing the risk of erosion. The tillage system did not affect any of the parameters studied. Water use efficiency (WUE) ranged from 5 to 14 kg ha^–1 mm^–1. Wheat and sunflower as preceding crops yielded poorer values for productivity and water utilization, while the best results were obtained with faba bean. The highest values of precipitation use efficiency (PUE) and WUE were reached with 100 kg N ha^–1 in all rotations except for wheat–sunflower, which needed 150 kg N ha^–1. The inclusion of faba bean or chickpea in a 2-yr rotation contributes to improve the WUE by wheat crop.

Abbreviations: CPI, crop precipitation interception index • PUE, precipitation use efficiency • WU, water use • WUE, water use efficiency

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
UNDER SPANISH MEDITERRANEAN CONDITIONS, rainfed wheat is planted in late autumn and completes its vegetative stage during mild winter conditions, when water deficit is unusual. The stem elongation–anthesis stage takes place during late winter and early spring when the water supply is very variable. The grain-filling period occurs during late spring when evaporative demand normally exceeds rainfall. Where water constitutes the limiting factor to crop production, the aim is to obtain the greatest amount of growth per unit of available water (Amir et al., 1991). However, measurement and interpretation of WUE in the field is often hampered by the high degree of complexity of these systems, due to season-to-season variability in rainfall, the variation in crop responses to soil types and to agronomic management (Asseng et al., 2001).

At least half of the increase in PUE over the last century can be attributed to improved agronomic management (Turner, 2004), although Stephens (2002) considers one-third attributable to new cultivars and two-thirds attributable to agronomic management. Water utilization can be improved by: increasing soil water storage, varying crop transpiration or raising root density. Management practices, such as tillage systems, nutrient supply, improved weed–disease–insect control, planting time and density, cropping sequences that minimize fallow periods, or use of adapted cultivars, can modify WUE (Angus and van Herwaarden, 2001; Turner, 2004; Nielsen et al., 2005). Strategies to increase crop growth in the vegetative phase might be expected to increase WUE when evaporation and vapor pressure deficits are low, since soil evaporation would be reduced by additional canopy cover (Angus and van Herwaarden, 2001). In many dryland environments, crops do not use all the water available in the soil profile because of restrictions to root growth. These restrictions may be physical, chemical, or biological. Agronomic practices that reduce the physical impedance to root growth can benefit dryland crop yields in water-limited environments (Turner, 2004). Many soil–surface modifications influence the components in the WUE equation. Such modifications, associated with some form of manipulation of the soil surface by tillage and surface residue management or mulching, can increase soil water retention capacity, improve the ability of roots to extract more water from the soil profile, or decrease leaching losses (Hatfield et al., 2001).

The soil environment remaining after certain crops synergistically improves the WUE of following crops (Anderson, 2005; Tanaka et al., 2005). The root system of some crops penetrates deeper, providing more "biopores" for a subsequent crop (Turner, 2004). According to Angus and van Herwaarden (2001), the reason for increased WUE by wheat following break crops is a healthier root system. This also allows a greater response to applied N. The WUE of some crops can be improved by more intensive cropping systems (Nielsen et al., 2002). Overall, PUE can be enhanced through adoption of more intensive cropping systems in semiarid environments (Hatfield et al., 2001). Intensified cropping systems improve our ability to use precipitation efficiently and are usually beneficial to the environment. Anderson (2005), in a comprehensive review, stresses scarcity of data available regarding the effect of previous crop and rotational sequence on WUE.

Increases in WUE and PUE derive from improved plant growth and yield resulting from proper soil nutrient status. Nitrogen management is linked to water use (WU) rates in cropping systems. The addition of N has an indirect effect on WU through the physiological efficiency of the plant (Hatfield et al., 2001). The largest increase in WUE in Mediterranean rainfed crops is obtained by altering the balance between evaporation and transpiration. Rapid canopy development, achieved through N fertilizer application or through a higher planting density, can result in a substantial reduction in soil evaporation and a corresponding increase in transpiration and grain yield (Debaeke and Aboudrare, 2004). However, Hatfield et al. (2001) found considerable divergence in the results reported in the literature on WUE related to soil nutrient management. Crop yields can vary in response to N management with no change in WU. Yunusa et al. (1993a and 1993b) reported that soil evaporation is barely, if at all, affected by the size of plant canopy of spring wheat grown under semiarid Mediterranean conditions. According to van Herwaarden et al. (1998), Angus and van Herwaarden (2001), and Halvorson et al. (2004), N fertilization can improve WUE; however, high N levels can reduce yields through "haying off" due to excess WU in the preanthesis period, leaving insufficient water for postanthesis grain filling. It is therefore important to balance N fertilization with available seasonal water supplies. Fischer (1981) suggests that in dryland environments there is an optimum biomass at anthesis, depending on available water, to maximize grain yield. While this appears to be true for heavy-textured soils, on sandy soils high N levels do not induce lower yields (Asseng et al., 2001). Nevertheless, Angus and van Herwaarden (2001) suggest that increasing vegetative growth with a high N status leads to a strong allocation of assimilate to structural tissue, and therefore to a potential shortage of soluble carbohydrate for retranslocation to grain.

The aim of this study was to compare the effects of tillage system, preceding crop, and N fertilizer on water utilization by wheat grown on a Vertisol under rainfed Mediterranean conditions.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The study was performed over a 6-yr period (1995–1996, 1996–1997, and 1999–2000 to 2002–2003) under rainfed Mediterranean conditions in a Vertisol. It was realized within a long-term experiment, called "Malagón," started in 1986. Experimental design was randomized complete block with a split-split plot arrangement and four blocks. Main plots were tillage system (no-tillage and conventional tillage); subplots were preceding crop, with four 2-yr rotations (wheat–sunflower, wheat–chickpea, wheat–faba bean, and wheat–bare fallow) and continuous wheat; sub-subplots were N fertilizer rate (0, 50, 100, and 150 kg N ha^–1) applied to wheat. Information about the site characteristic, crop management and statistical analyses has been provided in a companion paper (López-Bellido et al., 2007).

Soil water content was determined with two measurements per wheat plot at planting and harvest to a depth of 0.9 m using a ThetaProbe ML 2x Soil Moisture Sensor (AT Delta-T Devices, UK). Wheat grain was harvested in June using a 1.5 m wide Nurserymaster Elite Plot Combine (Wintersteiger, Austria) (30 m² per sub-subplot). Crop coverage (%) was determined as percentage of growing-season duration in both crops in the rotation relative to 2 yr (Huang et al., 2003). The CPI was calculated as the percentage of growing-season precipitation relative to annual precipitation. Schlegel et al. (1999) define PUE as grain yield divided by harvest-to-harvest precipitation, i.e., including growing-season plus preceding–fallow precipitation. Here, however, it is estimated as grain yield divided by growing-season precipitation, to determine the crop's ability to utilize precipitation once established (intercepted precipitation). Water use during the growing season, which includes the components of soil evaporation and crop transpiration, was determined as WU = R + SW_harvest – SW_planting, where R is rainfall over a defined period, and SW is soil water content (0–90 cm) at planting and harvest. Other terms in the water balance, surface runoff, and drainage were negligible. Water use efficiency was calculated by dividing grain yield by WU.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Crop Coverage and Crop Precipitation Interception Index
Of the five rotations studied, crop coverage for wheat–fallow lasted half as long as that of the remaining rotations, which provided mean coverage of 47% (Table 1). According to Conacher and Sala (1998), a high priority should be given to soil conservation practices to reduce the unsustainable soil rates in southern Spain. They stated that 40% of the land in this area has lost the A and part of the B horizons due to soil erosion by water. The CPI for wheat–fallow was 26%, thus exposing the land to a serious risk of erosion, especially under conventional tillage. Continuous wheat, wheat–faba bean, and wheat–chickpea intercepted a mean 51% of rainfall; and wheat–sunflower, 38% (Table 1). Both crop coverage and CPI were on the low side, even in the best rotations. Continuous wheat and faba bean, generally planted in late autumn, gave no ground coverage and offered no rainfall interception for just over half the autumn. Winter-planted chickpea and sunflower left ground bare throughout autumn and much of winter. The opportunity to displace the planting time of sunflower to autumn or winter was studied in southern Spain by Gimeno et al. (1989) who found that seasonal evapotranspiration was increased by 30% and WUE by 79% for winter plantings as compared with spring plantings. The tolerance of sunflower to low temperatures then becomes the main problem to solve through selection (Debaeke and Aboudrare, 2004). Soriano et al. (2004) and Barros et al. (2004) concluded that early plantings of sunflower (January) increase yields by increasing both WU and WUE. The disadvantage of low temperatures at early planting and a consequent delay in crop emergence is offset by a greater likelihood of more favorable moisture conditions, which are even more important for a fast and uniform crop establishment.

View larger version (15K): [in this window] [in a new window]   Fig. 1. Relationship among N rate and grain yield as a function of preceding crop in a rainfed wheat. Mean data from 6 yr. Vertical bars indicate LSD at P < 0.05 for comparison N rates: (a) within a preceding crop, and (b) between preceding crops. *, **, *** Significant at the 0.05, 0.01, and 0.001 probability level, respectively.

Fallow, faba bean, and chickpea as preceding crops displayed greater PUE than sunflower and continuous wheat (Table 3). This difference may largely be due to the achievement of optimum root density in both surface and deep soil, thus avoiding rapid evaporation or infiltration. However, it is also possible that rapid ground cover, achieved either through an appropriate choice of preceding crop or through N application, reduces evaporative flow and enhances short-term storage, thus giving the plant time to utilize rainfall. The tillage system x preceding crop interaction showed that PUE was higher under no-tillage for wheat monoculture; there was no difference between tillage systems for the other rotations (Table 4). According to Farahani et al. (1998), PUE can be improved by intensifying and diversifying the cropping system, and reducing noncrop periods.

There was no significant difference between the two highest rates for PUE (Table 3). Asseng et al. (2001) showed that application of N fertilizer increased PUE. Within each tillage system, the effect of fertilizer N rate was identical to the main effect (Table 5). Halvorson et al. (2004) reported that in a no-tillage dryland system PUE increased with N addition, reflecting the same trends as for grain yield, since precipitation did not vary with the N rate. Here, PUE increased with rising N fertilizer rates probably due to an improved root system and faster ground coverage in all rotations. In rotations with a poorer N supply, e.g., wheat–sunflower and wheat–chickpea according to López-Bellido and López-Bellido (2001b), PUE at fertilizer N rate of 150 kg N ha^–1 was significantly different from the rest of doses; in wheat–fallow and continuous wheat there was no difference between 100 and 150 kg N ha^–1; and in the wheat–faba bean rotation PUE was lower at 150 kg N ha^–1 than at 100 kg N ha^–1 (Table 4).

Water Use
Water use was significantly affected by yearly changes in weather conditions and rainfall (Table 2). Water use was not proportional to grain yield (Table 3). The data available do not furnish an explanation of this, although it is possible that WU was proportional to biomass, and that the results obtained reflect uneven vegetative growth in some years. The data for 1999–2000 make it difficult to confirm a clear trend, since that year was much higher, and water consumption lower, than in other years. This may be due to biological recovery of the system after no harvest the previous year, and also to a rainfall distribution pattern very different from that of other years, with a rainy autumn (257 mm) allowing an adequate level of water storage (López-Bellido et al., 2007), a dry winter (45 mm) ensuring a reasonable level of vegetative growth and a rainy spring (223 mm) that may have favored increased spike fertility. Wheat yield components would need to be analyzed to verify this hypothesis.

Although the main effect of tillage system was not significant, the year x tillage system interaction was (Table 2). Significant differences were recorded for 3 yr: WU was greater under no-tillage in 1999–2000 and 2000–2001, and lower in 2001–2002. These results cannot be readily accounted for, although greater WU would be expected under no-tillage in 1999–2000, since the no-tillage system tends to allow a slight increase in water storage in less rainy years. Water use was higher in faba bean, fallow, and chickpea rotations, and lower with sunflower and continuous wheat (Table 3). Tillage system x preceding crop was not significant (Table 2). Halvorson et al. (2000), in a 5-yr study of a wheat–fallow rotation, found no difference in WU between the two tillage systems. Nitrogen application increased significantly WU, although increasing N rates had no additional effect (Table 3). According to Corbeels et al. (1998), canopy cover is strongly affected by N, but this is not reflected in total WU or final dry matter yield.

Water Use Efficiency
All main effects except tillage system were significant for WUE (Table 2). Hatfield et al. (2001) suggest that it is possible to increase WUE by 25 to 40% through soil management practices that involve tillage. Year-on-year variations mirrored those of yield, except in 1996–1997, which displayed high WUE despite low yield, due to reduced WU (Table 3). Water use efficiency values differed considerably between seasons, ranging from 5 to 14 kg ha^–1 mm^–1. Aase and Pikul (1995) report WUE values ranging from 2.9 to 4.7 kg ha^–1 mm^–1, i.e., a lower range than that recorded here. By contrast, Corbeels et al. (1998) noted a WUE value of 11 kg ha^–1 mm^–1, with little variation, while Frech and Schultz (1984), in the Mediterranean-type conditions of Australia, obtained a range of 2 to 13 kg ha^–1 mm^–1.

Continuous wheat displayed WUE values lower than those of all rotations (Table 3). Huang et al. (2003) showed that rotations provide significantly improved wheat grain yields and WUE compared to standard wheat monoculture. The increase in WUE of rotations with regard to continuous wheat ranged from 2.9 to 3.3 kg ha^–1 mm^–1. Water use efficiency for continuous wheat was greater under no-tillage, while tillage system had no effect on WUE for the other rotations (Table 4). These results do not agree with those of Bonfil et al. (1999), although this may be because rainfall was heavier in the present study. These authors suggest that crop yield and WUE can be increased in arid zones with annual rainfall of <200 mm, through use of a wheat–fallow rotation system under a no-tillage system. Where annual rainfall is >200 mm, no-tillage management should be adopted to increase soil water content and WUE in continuous crops. Tanaka et al. (2005) reported that intensification of the cropping system, by introducing 6 to 8 wk of legume crop, may not produce large quantities of biological N, but N use efficiency and WUE by a succeeding wheat crop may increase because of disease suppression and growth-promoting substances released from decaying legume residues that promote healthier wheat roots (Stevenson and Van Kessel, 1996). According to Amir et al. (1991), the increase in yield and WUE for fallow treatment in comparison with continuous wheat cannot be ascribed to stored soil water. The data obtained in the present study, however, show that soil water content at planting was higher with preceding fallow than with continuous wheat (López-Bellido et al., 2007).

Water use efficiency increased with rising N fertilizer rates, although there was no significant difference between 100 and 150 kg N ha^–1 (Table 3). Hatfield et al. (2001) have suggested that modifying nutrient management practices, i.e., N rate, can increase WUE by 15 to 25%. On the contrary, Corbeels et al. (1998) showed no significant effect of N fertilization on WUE. Moreover, N management and its effect on WUE may be different in poorly drained soils (Hatfield et al., 2001). According to Amir et al. (1991), WUE is affected by N supply only when N becomes a deficient factor in the system, i.e., when water is not a limiting factor. For each N rate, WUE values were similar under both tillage systems (Table 5). Within each rotation, maximum WUE was recorded at fertilizer rates of 100 and 150 kg N ha^–1, with no significant difference between the two (Table 4).

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Under Mediterranean conditions, rainfed wheat in 2-yr rotation with fallow, faba bean, chickpea, or sunflower improves its WUE with regard to continuous wheat. Nevertheless, the choice of bare fallow as a tool to increase WUE does not seem very interesting in terms both economical and environmental, because no harvest is obtained and risk of erosion could be significant.

At water utilization and grain yield level, farmers should not expect major differences between no-tillage and conventional tillage. Year-on-year variations in weather conditions tend to offset, over the long term, potential benefits or drawbacks of each system for a given year.

Between tested N rates, the application of 100 kg N ha^–1 appears to be a low rate for the amount of water available to the wheat crop in rotation with chickpea and sunflower, 150 kg N ha^–1 being the more adequate rate. For wheat–faba bean rotation, 100 kg N ha^–1 gives significantly better results for water utilization and yield than 150 kg ha^–1.

	ACKNOWLEDGMENTS

 
We thank following for their excellent assistance in the laboratory and field work: Joaquín Muñoz, José Muñoz, and Auxiliadora López-Bellido. Our thanks are also expressed to ABECERA for providing the land and allowing us to use their field facilities. Special thanks are extended to INIA assisting with financial resources to conduct this long-term field experiment. This study was funded by the Spain's Plan Nacional I+D (Projects AGF95-0553, AGF97-0498, and AGL2000-0460).

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TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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				R. J. Lopez-Bellido, L. Lopez-Bellido, J. Benitez-Vega, and F. J. Lopez-Bellido Tillage System, Preceding Crop, and Nitrogen Fertilizer in Wheat Crop: I. Soil Water Content Agron. J., January 1, 2007; 99(1): 59 - 65. [Abstract] [Full Text] [PDF]

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