Crop Yields as Affected by Salinity

As noted in previous chapters of this manual, the quality of irrigation water is an important factor in determining sustainability of agriculture on salt-impaired lands. For a number of reasons, the availability of lowsalinity irrigation supplies has led to (1) an interest in using alternative supplies, such as recycled wastewaters, and (2) innovative plant and water management strategies to mitigate the adverse effects of salt and specificion stresses these poor-quality waters may impose on plant growth, yield, and quality. A second motivating factor is the lack of suitable drainage outlets in many agricultural areas of the world. Drainage of irrigated lands is one of the requisites for sustaining agricultural productivity in a given region over the long term. Adequate drainage not only allows for better aeration in the crop rootzone but provides a means by which salinity and toxic elements can be managed and controlled. Reuse of drainage water for irrigation is one way of expanding the useable water supply while at the same time reducing drainage volume. This chapter provides a management perspective on (1) how plants respond to salinity and toxic elements (e.g., Na , Cl , and B); (2) crop salt tolerance and the various factors that influence plant response to salinity; (3) the extent to which salinity affects crop yields and quality; and (4) management strategies to optimize yields by controlling soil salinity. It is not our intent to provide a comprehensive review of physiological effects of salinity crops. That topic is covered in detail in Chapter 6. CHAPTER 13

Plant Salt Tolerance

Behavior of 42 crop species grown in saline soils with high boron concentrations

In addition to nine major nutrients, eight micronutrients [i.e., boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn)] are also essential for healthy growth and reproduction of higher plants. Globally, crop production is largely dependent on chemical fertilizer use, especially in developed countries. While fertilizer use, particularly nitrogen (N) and phosphorus (P), has increased substantially in the past four decades in developing countries, such as Pakistan and India, fertilizer use is limited in many areas of the world where agriculture is constrained by harsh climatic conditions, especially low rainfall. The disparity between developed and developing countries is particularly acute with respect to micronutrient awareness and use. One area of the world that is characterized by major climatic and soil constraints, often exacerbated by unfavorable socioeconomic conditions, is the Middle East–West Asia region. This review provides a current perspective on that region of the world where crop yields are invariably low due to drought, with limited inputs and inherent soil nutrient deficiencies. With a high population, there is an urgent need to sustainably expand output. However, there is generally limited awareness of the potential significance of micronutrients in agriculture as factors in crop production, as well as limited research on micronutrients in most countries of the region. The long history of cultivated agriculture in the Middle East–West Asia region and the peculiar characteristics of its soils and climate predispose it toward problems of micronutrient deficiencies. Over three decades ago, a global study on micronutrients indicated widespread deficiencies of iron (Fe) and zinc (Zn), in contrast to copper (Cu) and manganese (Mn), but suggested the likelihood of excess levels of boron (B) in some countries of the region. This overview primarily addresses three focal points in the region, Pakistan in the east, Syria/Lebanon/Turkey in the center, and Spain on the western fringes, reflecting the zones of activity of the respective authors; the latter focal point is a developed region, where, because of soil and climatic similarities, the research is relevant to the whole Middle East–West Asia region. While providing some international context, this article brings together and summarizes published work in the areas of crop and soil micronutrient availability, their behavior in soils in relation to crop growth, and strategies to deal with either deficiency or toxicity, including crop selection for tolerance and subsequent genetic manipulation. Considerable strides have been made in elucidating the significance of both Zn and Fe in the region's mainly calcareous soils, through soil and plant analysis, with the resulting knowledge providing a sound basis for management interventions through validated field research. While B deficiency is common in some countries such as Pakistan, the problem of B toxicity (BT), where it exists, is only handled by crop adaptation. The review also highlights the implications of micronutrient constraints in the soil–plant–human–animal continuum. Intensification of agricultural production as a result of overall macronutrient use, expansion of irrigation, and introduction of new or “niche” crops is likely to accentuate micronutrient deficiencies in the region, but developments such as conservation agriculture may counteract this trend. As the trend for land-use intensification increases because of higher yields due to fertilizer use and irrigation and the introduction of new crops, and as other nutrient constraints are eliminated, micronutrients will inevitably assume greater significance in the future agriculture of the Middle East–West Asia region together with improvements in plant breeding and crop management.

Micronutrient constraints to crop production in the Middle East-West Asia region: significance, research, and management

Soil and plant analyses are useful diagnostic tools only if they supply adequate information about the current state and can predict effects of different types of management. The prerequisites for reproducibility and consistency may not be met with boron which is not distributed homogeneously in plants. It accumulates in marginal areas and between veins, is transported with the transpiration stream and accumulates at terminal places of transpiration. The boron concentration within the same leaf may vary 100‐fold and foliar analyses represent an average value only. Moreover, the boron content increases with the age of leaves, and there is no indication of a homeostatic control of foliar boron contents. Accurate, representative sampling may thus be difficult and critical. An extreme case is shown where toxicity occurs in old leaves and deficiency in new growth. The rate of transpiration greatly affects boron transport into leaves and its distribution. Predictions must thus take water relations into...

Non-homogeneity of boron distribution in plants and consequences for foliar diagnosis

The boron tolerance of two summer squash cultivars (Cucurbita pepo L ‘Aristocrat Zucchini’ and ‘Peter Pan Scallop’) and one winter squash cultivar (Cucurbita moschata Poir ‘Butter boy’) was determined in large, outdoor sand cultures Boron treatments were imposed by irrigation with culture solutions that contained 10, 30, 60, 90, 120, or 150 mg B L-1 Relative fruit yields of ‘Zucchini’, ‘Scallop’, and ‘Butter boy’ were reduced 52%, 98%, and 43% with each unit (mg L-1) increase in soil solution B (Bsw)>27, 49, and 10 mg B L-1, respectively Reduced yields of all cultivars were attributed to a reduction in fruit number and not fruit size Boron concentrations in leaves and fruit were directly correlated to Bsw

L. E. Francois

Papers

Effect of excess boron on summer and winter squash