Plant breeding and drought in C3 cereals: what should we breed for?

Irrigation management under water scarcity

Water shortage in China, particularly in the north and northwest of China, is very serious. The region accounts for half of the total area of China, but has less than 20% of total national available water resources. While the water shortage in this region is severe, irrigation water use efficiency is only about 40%, with a typical agricultural water use efficiency of about 0.46 kg m(-3). Excessive irrigation in Ningxia and Inner Mongolia has had a significant influence on downstream water users along the Yellow River. It is widely believed that an increase in the agricultural water use efficiency is the key to mitigating water shortage and reducing environmental problems. This paper reviews water-saving agricultural systems and approaches to improve agricultural water use efficiency in the and and semiarid areas of China. The paper will cover biological mechanisms of water-saving agriculture and water-saving irrigation technologies, including low pressure irrigation, furrow irrigation, plastic mulches, drip irrigation under plastic, rainfall harvesting and terracing, In addition, the paper addresses the compensatory effect of limited irrigation and fertilizer supplementation on water use efficiency and highlights the need to breed new varieties for high water use efficiency. Considerable potential for further improvement in agricultural water use efficiency in the region depends on effective conservation of moisture and efficient use of the limited water. (c) 2005 Elsevier B.V. All rights reserved.

Improving Agricultural Water Use Efficiency in Arid and Semi-arid Areas of China

http://www.cropscience.org.au/icsc2004/pdf/2085_deng.pdf

Improving agricultural water use efficiency in arid and semiarid areas of China

Drylands occupy 6.15 billion hectares (Bha) or 47.2% of the world’s land area. Of this, 3.5 to 4.0 Bha (57%–65%) are either desertified or prone to desertification. Despite the low soil organic carbon (SOC) concentration, total SOC pool of soils of the drylands is 241 Pg (1 Pg = petagram = 1015 g = 1 billion metric ton) or 15.5% of the world’s total of 1550 Pg to 1-meter depth. Desertification has caused historic C loss of 20 to 30 Pg. Assuming that two-thirds of the historic loss can be resequestered, the total potential of SOC sequestration is 12 to 20 Pg C over a 50-year period. Land use and management practices to sequester SOC include afforestation with appropriate species, soil management on cropland, pasture management on grazing land, and restoration of degraded soils and ecosystems through afforestation and conversion to other restorative land uses. Tree species suitable for afforestation in dryland ecosystems include Mesquite, Acacia, Neem and others. Recommended soil management practices include application of biosolids (e.g., manure, sludge), which enhance activity of soil macrofauna (e.g., termites), use of vegetative mulches, water harvesting, and judicious irrigation systems. Recommended practices of managing grazing lands include controlled grazing at an optimal stocking rate, fire management, and growing improved species. The estimated potential of SOC sequestration is about 1 Pg C/y for the world and 50 Tg C/y for the U.S. This potential of dryland soils is relevant to both the Kyoto Protocol under UNFCCC and the U.S. Farm Bill 2002.

http://www.tinread.usarb.md:8888/tinread/fulltext/lal/ecosystems.pdf

Carbon sequestration in dryland ecosystems.

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 Ritchie's 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 efficiency and transpiration efficiency of wheat under rain-fed conditions and supplemental irrigation in a Mediterranean-type environment

Although limited amount of water is the primary constraint to agricultural productivity in the rainfed area of West Asia and North Africa (WANA), yields are also low because of the poor mineral nutrient status of soils. Yields can, therefore, be considerably increased by judicious fertilizer use. Laboratories for soil and plant analysis are essential for identifying nutrient constraints and providing a basis for efficient fertilizer use, through correlation studies to establish suitable soil testing extractants and calibration studies with crop responses. The Soils Laboratory at the International Center for Agricultural Research in the Dry Areas (ICARDA) has initiated a quality control program among the national agricultural research systems (NARS) in the countries of the WANA region. The efforts include linkages with the Wageningen International Soil Analytical Exchange Program, in‐country training courses, and a laboratory analysis manual. Continued improvement in laboratory performance is depe...

Assessment of soil and plant analysis laboratories in the West Asia‐North Africa Region

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...

Nitrogen mineralization potentials of selected mediterranean soils

In dryland fanning of the Mediterranean zone, which has rain in the winter with long dry summers, inadequate soil moisture is generally the dominant factor limiting crop growth. Nitrogen (N) and phosphorus (P) can significantly and economically increase yields in most circumstances when both elements are deficient. However, soil testing for fertilizer recommendation is in its infancy in the vast area of West Asia‐North Africa (WANA) with a winter rainfall climate. Fundamental to such endeavors is the use of appropriate tests and consistency of test results. Thus, a standard soil sample (Vertic Xerochrept), along with a questionnaire, was sent to 50 laboratories in the region which are involved with soil analysis. Of the 22 respondents, most tested for available nutrients, pH, and electrical conductivity (EC), but few did tests for total P, boron (B), or sulfur (S). Most laboratories made recommendations for clients. Few laboratories were involved with 15N or 32P analysis, while a small number per...

Soil test standardization in west Asia‐North Africa Region

Climate, particularly rainfall, has a dominant influence on soil properties, and consequently on vegetation and land use. In semi‐arid areas of the world, seasonal rainfall and its distribution determines crop yields and may influence soil formation and biological processes that affect soil nutrient availability. Thus, we conducted a fertility survey in northern Syria's dryland zone across a rainfall gradient, from the arid steppe with less than 200 mm/yr to the wetter wheat‐producing areas with up to 715 mm in some years. This involved sampling of five experimental stations, i.e., Maragha (190 mm), Boueidar (223 mm), Breda (263 mm), Tel Hadya (330 mm), and Jindiress (446 mm), and farmers’ fields in the vicinity of these stations. Nutrient distribution with profile depth was also measured on the stations. The most consistent trend with increasing rainfall was a decrease in calcium carbonate (CaCO3). Similarly, boron (B) tended to be higher in the drier sites, especially in the sub‐soil. Total nit...

S. Garabet

Papers

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

Assessment of soil and plant analysis laboratories in the West Asia‐North Africa Region

Nitrogen mineralization potentials of selected mediterranean soils

Soil test standardization in west Asia‐North Africa Region

Geographical distribution of soil test values in Syria and their relationship with crop response