Abstract
The utilization of reclaimed wastewater is a suitable and sustainable approach to agriculture production in water-scarce regions. However, even though the wastewater is treated to reduce nutrient concentration such as phosphorus, the 10,600 to 14,006 m3 of water applied ha−1 year−1 on grass and alfalfa hay crops in Nevada can lead to soil phosphorus buildup over an extended period. This study evaluated the effectiveness of forage systems (FS) of monoculture grass, monoculture legume, and their mixtures on herbage accumulation, tissue phosphorus concentration, and quantity of phosphorus removed from a grassland under wastewater irrigation. The study was carried out at the Main Station Field laboratory in Reno, Nevada, USA. A total of 23 FS using tall fescue (Schedonorus arundinaceus (Schreb.) Dumort), alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.) and white clover (Trifolium repens L.) in monocultures or grass–legume mixtures (25:75, 50:50, and 75:25) based on seeding rate were used. The response variables were herbage accumulation (HA), tissue phosphorus concentration, and phosphorus removal. Forage systems means were considered different P ≤ 0.05. Herbage accumulation, tissue phosphorus concentration, and phosphorus removal differed among FS and year. Herbage accumulation was similar for the grass monocultures (10.5 Mg ha−1; SE = 1.1) and the majority of the grass–legume mixtures (9.0 Mg ha−1; SE = 1.1) but both systems had greater HA than legumes monoculture (4.3 Mg ha−1; SE = 1.1). The legume monocultures of alfalfa and white clover had the greatest phosphorus concentrations (10.9 g kg−1 dry matter; SE = 0.44) among all FS. Total phosphorus removed was least among legume monocultures (34.0 kg P ha−1; SE = 6.2) in this study and generally similar for grass monocultures (67.4 kg P ha−1; SE = 6.2) and grass–legume mixtures of 75:25 (61.7 kg P ha−1; SE = 6.2). Based on the response variables, agronomic, and environmental considerations a grass–legume mixture that includes 75:25 or even a 50:50 seeding rate ratio will be suitable options for phosphorus removal from phosphorus enriched grasslands in semiarid ecosystems that utilized wastewater for irrigation.
Highlights
Agricultural production in semiarid and arid regions of the world is constrained by water scarcity and nutrient-poor soils [1]
This study evaluated the effectiveness of forage systems of monoculture grass, monoculture legume, and their mixtures on herbage accumulation, tissue phosphorus concentration, and quantity of phosphorus removed from a grassland under wastewater irrigation
In 2018, annual herbage accumulation was greater for grass–legume mixture 6, and both cultivars of tall fescue monocultures than the monoculture legumes, and grass–legume mixtures 1, 2, and 11 (Table 2)
Summary
Agricultural production in semiarid and arid regions of the world is constrained by water scarcity and nutrient-poor soils [1]. In water-scarce agroecosystems, crop production agriculture is heavily reliant on irrigation as the sporadic precipitation that accrued annually is insufficient to maximize crop growth and yield. This scarcity in water for agricultural production in these regions is further exacerbated by climate change and the associated events of frequent and intensive droughts that cause a reduction in water resources in semiarid and arid regions [2,3]. The benefits of utilizing reclaimed wastewater are multiple, in that it provides a reliable year-round source of water for crop production [3], crop yield optimization through the provision of nutrients such as N, P, and K [9,10,11], reduced demand on fossil fuel for synthetic fertilizer production, minimize fertilizer input cost [3], increase crop farm profit margins [12], and enhance environmental conservation due to a reduction in synthetic fertilizer use [13]
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