Search

Cover crops can provide a wide range of ecosystem services including soil water conservation, improved soil nutrient supply and retention, and enhanced crop yields. However, achieving these services in dryland cropping systems can be highly challenging, and cover crops may carry a greater risk of causing ecosystem disservices. Assessment of the balance of ecosystem services vs disservices is critical for understanding the potential role of cover crops within dryland cropping systems. The objective of this meta-analysis was to assess the effects of cover cropping in drylands on soil water and soil mineral nitrogen content at sowing of subsequent cash crops and their yields compared to control fallows. A total of 38 articles were examined, for a total of 1006 cash crop yield, 539 soil water, and 516 soil mineral nitrogen independent studies, spanning the period 1994–2021. On average, cover cropping reduced cash crop yield by 7%, soil water content by 18%, and soil mineral nitrogen by 25%, with significant variation across climates, soil types, and crop management conditions. Subsequent cash crop yields changed by +15, +4, −12, and −11% following cover crops in tropical, continental, dry, and temperate dryland climates, respectively. The most significant yield benefits were proportionate to soil water content and soil mineral nitrogen at the time of cash crop sowing. This is the first meta-analysis to demonstrate that minimum annual precipitation of ~700 mm represents a "break-even" point to realize significant cash crop yield benefits of cover cropping compared to control fallows in dryland environments. The successful incorporation of cover crops into dryland cropping systems requires careful planning based on context-specific biophysical conditions to minimize trade-offs between ecosystem services and disservices. [ABSTRACT FROM AUTHOR]

Dorycnium hirsutum (L.) Ser. and Dorycnium rectum (L.) Ser. are Mediterranean perennial legumes that may have potential as alternative forage plants to Medicago sativa (lucerne, alfalfa) for low rainfall dryland agriculture. Strategies for surviving periods of water deficit are vital for perennial plants in water-limited environments. This experiment compared leaf physiological and morphological adaptations to increasing water deficit among D. hirsutum, D. rectum and M. sativa. Plants were grown in the glasshouse in large pots (7.8 L, 1 m deep, 10 cm diameter) containing a sandy clay loam (14% available water content) to limit differences between root foraging among the species. Watering was withheld for 21 days and predawn and midday leaf water and osmotic potential were determined. Mid-morning rates of gas exchange were measured at five times as soil water was depleted. After 35 days of withholding water, plant recovery was measured. D. hirsutum and M. sativa reduced stomatal conductance at leaf water potentials below −1.8 MPa and water-stressed D. hirsutum osmotically adjusted by up to 0.68 MPa. D. rectum differed from the other species; leaf water potential was maintained at high levels until soil water content had reached low levels, and reductions in stomatal conductance and photosynthesis were not associated with leaf water potential. D. hirsutum and M. sativa displayed leaf morphological adaptations that may contribute to greater resistance of water deficit. Only one of five D. rectum plants survived the water-stress treatment compared to five of five for D. hirsutum and four of five for M. sativa. The water relations and physiology of D. hirsutum observed in this study suggest that it possesses adaptations suitable for arid environments. On the other hand, the poor survival and water relations of D. rectum indicate that it is poorly adapted to situations where water deficit is common. [ABSTRACT FROM AUTHOR]