THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF CITRUS (CITRUSSPP.): A REVIEW

Abstract

SUMMARYThe results of research on the water relations and irrigation need of Citrus spp. are collated and reviewed in an attempt to link fundamental studies on crop physiology to drought mitigation and irrigation practices. Background information is given on the centres of origin (south-east Asia) and of production of citrus (areas with subtropical Mediterranean-type climates). The effects of water stress on the development processes of the crop are summarised followed by reviews of the plant water relations, crop water requirements, water productivity and irrigation systems. The topic is complicated by the diversity of species and cultivars (including rootstocks) that are embraced within Citrus spp. The effects of water availability on vegetative growth are understood in general terms, but the relationships have not yet been quantified. Similarly, the need for a ‘rest period’ to induce flowering is understood, but its magnitude (in terms of a drought stress index or day-degrees) does not appear to have been specified with precision. Again, the effects of drought on flower and fruit formation and retention are understood in general terms, but the relationships have not been quantified in useful ways for specific cultivars. Rooting depth and distribution have only been described in a limited number of situations. Environmental factors influencing stomatal conductances are generally well described and relationships with some growth processes established. Compared with other crops, low stomatal/canopy conductance restricts water use of Citrus spp. Some (limited) progress has been made in quantifying crop water requirements in specific conditions. Despite many recent attempts to specify how little water can be applied at specific growth stages to optimise water productivity through regulated deficit irrigation, no consensus view has emerged. The yield response to ‘full’ irrigation is of the order 6–7 kg fresh fruit m−3 as a result of an increase in the number of fruit of marketable size. There are also improvements in fruit quality. The most effective way of irrigating a citrus orchard is with a microirrigation system (drip or microsprinklers), but both methods require answers to the question: what proportion of the root zone needs to be irrigated? Both methods, especially drip, allow water to be applied (with fertigation) at very frequent intervals (including several times a day), although formal evidence of the benefits to be obtained from this level of intensification is lacking.

Impacts of climate change on drought: changes to drier conditions at the beginning of the crop growing season in southern Brazil

“…Th e high number of signifi cant decreasing trends found in the monthly series of October and; iii. Th e fact that the analyzed trimester match with critical growth stages of several crops (Carr 2012), we indicate the presence of changes in the climatic patterns of the crop growing season that should be considered in public policies such as the crop zoning. The analyses performed at other time scales (4 to 12-month) are consistent with those depicted in Figure 3, adding little information to the trend assessment.…”

Effects of long-term summer deficit irrigation on ‘Navelina’ citrus trees

“…Although in citrus, water use efficiency (WUE, Table 3) may be affected by the timing 425 and fruit stage where the water restriction is applied (Carr, 2012), in this case, it is evident 426 that summer RDI treatments provided significantly higher WUE than the control treatment, as 427 is generally associated (Fereres and Soriano, 2007) LIST OF TABLE CAPTIONS Table 1. Rainfall and evaporative demand (ETo) registered at the meteorological station nearest to the experimental plot during the studied period.…”

“…Many works have proved the feasibility and effectiveness of 62 this practice by reducing water use in tree crops with low or null impact on yield and fruit 63 quality (e.g. Carr, 2012;Ruiz-Sánchez et al, 2010). 64…”

Evaluation of some Modified Flood Irrigation Methods on Growth and Fruit Quality of Valencia Orange Trees under Sandy Soil Conditions

“…This can be due to in the DR, SR and SS the trees received the required irrigation water easily since the irrigation water is well distributed around the tree canopy and the potential wet area is higher. In this respect, Carr (2012) declared that shoot growth and elongation occurs when the irrigation water is available. Labanauskas et al (1966) on orange seedlings, pointed out that moisture content of the soil influenced nutrients uptake, translocation, and distribution within citrus plants, and that might contribute to vegetative flushes.…”