Influence of Lateral Spacing and Irrigation Frequency on the Performance of Surface and Subsurface Drip Irrigation Systems: A Critical Narrative Review

Abstract

Lateral spacing and irrigation frequency are two of the most frequently manipulated design and management variables in surface and subsurface drip irrigation, yet their combined influence on crop performance remains inconsistently characterised across the agronomic and irrigation engineering literature. This review critically synthesises evidence on how these two variables shape soil-water and nutrient distribution, root-zone uniformity, crop yield, and water productivity across a range of crops, soil textures, and climates. Evidence was drawn from field experiments, meta-analyses, and mechanistic modelling studies identified through a structured search of engineering, agronomic, and horticultural databases. The synthesis indicates that lateral spacing effects are strongly soil-texture dependent: in deep, fine-textured soils with substantial lateral hydraulic redistribution, widening spacing from narrow to moderate intervals often produces negligible yield penalties, whereas in coarse-textured or shallow soils, and for crops with fibrous or shallow root systems, wider spacing consistently depresses yield and distribution uniformity. Irrigation frequency shows a comparable pattern of context-dependence: on deep silt loam soils with high water-holding capacity, frequency has repeatedly shown little influence on yield, whereas on sandy soils and for high-frequency-demanding vegetable and root crops, frequency interacts strongly with irrigation rate and nitrogen management to determine outcomes. The two variables are mechanistically linked through their joint control of wetting-pattern overlap, yet very few studies have applied genuinely factorial spacing-by-frequency designs, and most research has been geographically concentrated in a small number of arid and semi-arid production regions. Meta-analytic evidence broadly favours narrower spacing and higher frequency for maximising yield and water productivity, but the magnitude of benefit is frequently smaller than the additional capital and operating cost implied, so that economically optimal design choices do not always coincide with agronomically optimal ones. The review identifies the absence of standardised, soil-texture-stratified factorial trials as the principal barrier to generalisable design guidance and proposes priority research directions accordingly. The findings carry direct relevance for irrigation engineers, agronomists, and policy makers seeking to reconcile water-saving objectives with capital efficiency in drip system design.