Mustafa Pala

Water-use efficiency and transpiration efficiency of wheat under rain-fed conditions and supplemental irrigation in a Mediterranean-type environment

Growth and water use were measured in wheat (Triticum aestivum L.) grown in northern Syria in a typical Mediterranean climate over five seasons 1991/92–1995/96. Water use was partitioned into transpiration (T) and soil evaporation (Es) using Ritchies model, and water-use efficiency (WUE) and transpiration efficiency (TE) were calculated. The aim of the study was to examine the influence of irrigation and nitrogen on water use, WUE and TE. By addition of 100 kg N ha-1, Es was reduced from 120 mm to 101 mm under rain-fed conditions and from 143 mm to 110 mm under irrigated conditions, and T was increased from 153 mm to 193 mm under rain-fed conditions and from 215 mm to 310 mm under irrigated conditions. Under rain-fed conditions, about 35% of evapotranspiration (ET) may be lost from the soil surface for the fertilized crops and 44% of ET for the unfertilized crops. Transpiration accounted for 65% of ET for the fertilized crops and 56% for the unfertilized crops under rain-fed. As a result of this, WUE was increased by 44% for dry matter and 29% for grain yield under rain-fed conditions, and by 60% for dry matter and 57% for grain yield under irrigated conditions. Transpiration efficiency for the fertilized crops was 43.8 kg ha-1 mm-1 for dry matter and 15 kg ha-1 mm-1 for grain yield, while TE for the unfertilized crops was 33.6 kg ha-1 mm-1 and 12.2 kg ha-1 mm-1 for dry matter and grain yield, respectively. Supplemental irrigation significantly increased post-anthesis water use, transpiration, dry matter and grain yield. Water-use efficiency for grain yield was increased from 9.7 to 11.0 kg ha-1 mm-1 by supplemental irrigation, although WUE for dry matter was not affected by it. Irrigation did not affect transpiration efficiency for grain yield, but decreased transpiration efficiency for dry matter by 16%. This was associated with higher harvest index as a result of good water supply in the post-anthesis period and increased transpiration under irrigated conditions.

Water use and water-use efficiency of chickpea and lentil in a Mediterranean environment

Water supply is a major constraint to crop production for both chickpea and lentil in West Asia and North Africa, both of which have a Mediterranean climate. This study examined water use and water-use efficiency of chickpea and lentil from 3 experiments over 12 seasons, 1986–87 to 1997–98, in northern Syria. The strongest determinant of grain yield of chickpea and lentil and their water use under rainfed conditions is rainfall and its distribution. Large inter-seasonal fluctuations in weather resulted in larger inter-seasonal fluctuations in water use, and therefore in production of legumes. Seasonal evapotranspiration (ET) was significantly correlated with seasonal rainfall for both chickpea and lentil. Mean ET over 12 seasons was 268 mm for chickpea and 259 mm for lentil. The depth of extraction was, on average, 120 cm for chickpea and 80 cm for lentil. The average extractable soil water was 125 mm for chickpea and 90 mm for lentil over 12 seasons. For lentil, water-use efficiency for dry matter (WUEdm) and for seed yield (WUEgr) was 13.7 and 3.8 kgsha.mm, respectively; for chickpea, WUEdm and WUEgr, 8.7 and 3.2 kgsha.mm, respectively. Supplemental irrigation can significantly increase grain yield of both chickpea and lentil. However, there was less increase in grain yield in the wet seasons than in the dry seasons. Estimated soil evaporation was 80 mm for lentil and 105 mm for chickpea. The average transpiration efficiency was 7.1 kgsha.mm for lentil and 6.4 kgsha.mm for chickpea. Estimated potential transpiration efficiency for seed yield was 11.8 kgsha.mm for lentil and 12.2 kgsha.mm for chickpea. Both the average water-use efficiency and potential transpiration efficiency for lentil and chickpea were lower than those for cereals. Despite this, the rotation benefits and higher economic return provide the potential for these legumes to replace fallow or to break continuous cereal cropping in the regions farming system.

Simulation of durum wheat (Triticum turgidum ssp. durum) growth under different water and nitrogen regimes in a mediterranean environment using CropSyst

Abstract CropSyst, a cropping system simulation model, was evaluated for its ability to simulate growth, yield, and water and nitrogen use of two wheat cultivars (Cham 1 and Hourani). These cultivars were grown under different water (rainfed, 60% and 100% of crop water requirements) and nitrogen (without and with 100 kg N/ha) regimes in a Mediterranean type of environment at the Tel Hadya Research Station of ICARDA. Data from three contrasting growing seasons (1989/90 to 1991/1992) were used in these simulations. Soil characteristics, initial conditions of available moisture, N and organic matter, and daily weather data were input to CropSyst. Crop input parameters were mostly selected from the model documentation or determined from the experimental data. A few cultivar-specific parameters were adjusted within a narrow range of typical fluctuation by model calibration. Results showed that CropSyst was generally able to simulate evapotranspiration, crop N content, green leaf area, aboveground biomass, and grain yield as observed in the field experiments. Overall, the magnitude of the root mean square errors was about 10% of the observed means with two exceptions (25% and 32%). Index of agreement between predicted and observed values fluctuated from 0.90 to 0.98 (a value of 1.0 indicating excellent agreement), with most values equal or better than 0.95.

Crop row spacing and its influence on the partitioning of evapotranspiration by winter-grown wheat in Northern Syria

A study was conducted during the 1996–97 crop growth season at ICARDA in northern Syria, to investigate the influence of wheat canopy architecture on the partitioning of moisture between soil evaporation and crop transpiration, on a soil with high hydraulic conductivity. The study was conducted on the long-term two course wheat-lentil rotation trial, established on a swelling clay soil (Calcixerollic xerochrept). The wheat canopy architecture was manipulated by sowing the crop at either of two row-spacings, 0.17 or 0.30 m, both at a constant sowing rate equivalent to 120 kg ha−1. In this study, evapotranspiration from the crop was inferred from changes in soil moisture content over time, evaporation and rainfall interception were measured daily using microlysimetry, drainage was estimated as being the difference between potential daily evapotranspiration, and the evapotranspiration estimated from the soil water deficit. Between sowing and day 80 (tillering stage), evapotranspiration was calculated to consist mainly of soil evaporation. However, after day 80, transpiration became an increasingly dominant component of evapotranspiration. For both row-spacings, cumulative evapotranspiration over the season was approximately 373 mm. In the narrow-row crop, transpiration and soil evaporation were approximately 185 mm and 183 mm of water respectively. Conversely for the wide row-spaced crop, 172 mm of water was transpired while about 205 mm of water evaporated from the soil surface. While green leaf area index did not differ between row-spacings, the architecture of the crops as a result of sowing affected solar radiation penetration such that more incident radiation was intercepted at the soil surface of the wide row-spaced crop. This is likely to have made some contribution to the elevated levels of evaporation from the soil beneath the canopy of the wide-sown crop.

Long‐Term Cereal‐Based Rotation Trials in the Mediterranean Region: Implications for Cropping Sustainability

With increasing global populations particularly in developing countries, and a limited or even shrinking supply of arable land, the challenge to agriculture is to meet the worlds food and fiber needs without reducing the capacity of the resource base (soil and water) to enable guaranteed production for posterity and also to accommodate societys environmental and energy concerns. The issue of production sustainability is all the more acute in semi‐arid and arid regions of the world where drought and related biophysical factors create a fragile and uncertain environment for production. In the West, mainly in temperate regions, long‐term agronomic trials have been invaluable in identifying new technologies and crop management systems that have contributed to enhanced crop output that is sustainable from the biological, environmental, and economical standpoints. Many of these trials continue to guide cropping trends into the foreseeable future. The Mediterranean region has served climatic constraints to its agriculture and despite being cultivated for millennia, it is largely food deficient. Yet long‐term cropping experiments that could direct agricultural production in a sustainable manner are relatively rare, and even most of such trials are of recent vintage. This review offers a background perspective on factors related to crop, production, and subsequently examines the various multiyear cropping system/tillage trials in countries of North Africa and West Asia that border the Mediterranean. Special emphasis is given to the wide range of trials conducted in Syria by the International Center for Agriculture Research in the Dry Areas across a range of rainfall zones that are typical of the region as a whole. The goal of many trials was to identify cropping systems as a substitute for fallow and continuous cereal cropping with implications for improved water‐use efficiency (WUE), crop quality, soil quality, and fertilizer use. Lessons learned from the trials are highlighted as well as future directions for cropping systems research.

Tillage systems and stubble management in a Mediterranean-type environment in relation to crop yield and soil moisture.

The effect of tillage and crop rotations can only be seen over many crop years. Crop yield and soil results are evaluated from two long-term trials, established in 1978–79 and 1985–86 to investigate various forms of tillage and the timing of such operations in various wheat ( Triticum aestivum )-based rotations on a Calcixerollic Xerochrept in northern Syria. In a tillage systems trial involving two wheat–legume–watermelon ( Citrullus lanatus ) rotations, deep tillage showed no advantage over a shallow sweep-tillage system, either for soil moisture storage or yield increase of any crop. The zero-till system suited legume crops but gave lower productivity in wheat due to a build up of grassy weeds, and was not suitable for watermelon. Minimum tillage, with its higher energy-use efficiency and yield levels equal to or even slightly above those of deep-tillage systems, appears promising for the lowland areas of West Asia and North Africa. In a tillage timing trial, wheat in a wheat–lentil ( Lens culinaris ) rotation yielded best after conventional deep disc-plough tillage, but lentil yields were higher in a zero-till system.

Crop sequences, nitrogen fertilizer and grazing intensity in relation to wheat yields in rainfed systems.

The Mediterranean region is experiencing unrelenting land-use pressure, largely driven by population growth. Long-term cropping system trials can guide crop and soil management options that are biophysically and economically sustainable. Thus, an extensive cereal-based rotation trial (1983-98) was established in northern Syria, to assess various two-course rotations with durum wheat (Triticum turgidum Desf.). The alternative rotations were: continuous wheat, fallow, chickpea (Cicer arietinum), lentil (Lens culinaris), medic (Medicago spp.), vetch (Vicia sativa) and watermelon (Citrullus vulgaris) as a summer crop. Ancillary treatments were: nitrogen (N) fertilizer application to the cereal phase (0, 30, 60 and 90 kg N/ha) and variable stubble grazing management (zero or stubble retention, moderate and heavy grazing). Both phases of the rotation trial occurred each year. The soil is a fine clay, thermic Calcixerollic Xerochrept. Seasonal rainfall was the dominant factor in influencing overall yields. Rotations significantly influenced yields, being highest for fallow (2·43 t/ha), followed by watermelon (similar to fallow), vetch, lentil, medic and chickpea, and least for continuous wheat (1·08 t/ha). Overall, yields increased consistently with added N, but responses varied with the rotation. The various stubble grazing regimes had little or no effect on either grain or straw yields. While the trial confirmed the value of fallow and the drawbacks of continuous cereal cropping, it also showed that replacing either practice with chickpea or lentil, or vetch for animal feed, was potentially a viable option. Given favourable economics, legume-based rotations for food and forage could contribute to sustainable cropping throughout the Mediterranean region.

Yield gap analysis: modelling of achievable yields at farm level

This chapter quantifies the potential yields and yield gaps between the potential and the actual yields obtained by the farmers for the major rainfed crops grown in the selected countries in South and South East Asia (India, Thailand and Vietnam), SSA and the West Asia and North Africa (WANA) region, where food security is increasingly threatened because of expected increase in population and degradation of natural resources. This analysis is expected to help identify the opportunities and constraints for yield improvement with the implementation of the improved crop production and natural resource management technologies for the rainfed regions.

Assessing the sustainability of wheat-based cropping systems using simulation modelling: sustainability = 42?

Abstract Concepts of agricultural sustainability and possible roles of simulation modelling for characterising sustainability were explored by conducting, and reflecting on, a sustainability assessment of rain-fed wheat-based systems in the Middle East and North Africa region. We designed a goal-oriented, model-based framework using the cropping systems model Agricultural Production Systems sIMulator (APSIM). For the assessment, valid (rather than true or false) sustainability goals and indicators were identified for the target system. System-specific vagueness was depicted in sustainability polygons—a system property derived from highly quantitative data—and denoted using descriptive quantifiers. Diagnostic evaluations of alternative tillage practices demonstrated the utility of the framework to quantify key bio-physical and chemical constraints to sustainability. Here, we argue that sustainability is a vague, emergent system property of often wicked complexity that arises out of more fundamental elements and processes. A ‘wicked concept of sustainability’ acknowledges the breadth of the human experience of sustainability, which cannot be internalised in a model. To achieve socially desirable sustainability goals, our model-based approach can inform reflective evaluation processes that connect with the needs and values of agricultural decision-makers. Hence, it can help to frame meaningful discussions, from which actions might emerge.

Nitrogen mineralization potentials of selected Mediterranean soils

Abstract To gain a better understanding of N availability in Mediterranean soils, 18 surface (0–20cm) soil samples were selected from soil groups of Syria for study of their N mineralization potentials. The chosen soils represented the predominant soil groups found in West Asia and North Africa, i.e. Inceptisols, Vertisols, Aridisols, Mollisols and Entisols. Soils were incubated in tubes at 25 ± 0.5°C after addition of N‐free nutrient solution according to the method used by Stanford and Smith (18). Mineralized N was recovered from tubes by leaching with nutrient solution at 2 week intervals up to 22 weeks of incubation; NH4 and NO3 nitrogen were analyzed in the leachates. The N mineralization potential (No) was estimated using three procedures: (i) application of the empirical linear equation suggested by Stanford and Smith (18) relating (No) to the slope of N mineralized (Nt) with the square root of time (t) i.e., No = 6.5 (δNt/δt1/2); (ii) the exponential equation Nt = No [(1‐exp (‐kt)], with calculati...