Use of Amino Acids and Slow-Release Urea-Based Biostimulants to Enhance Yield and Grain Quality in Durum Wheat Under No-Tillage Conditions in Semi-Arid Region

Optimizing resources to produce higher quality food is key to promoting more resilient agroecosystems. Although the use of biostimulants in agriculture has been gaining importance in recent years, their success depends on edaphoclimatic conditions and on the specific plant species. For this reason, the main aim of this study was to evaluate the effect of biostimulants (amino acids obtained from the enzymatic hydrolysis of plant extracts) on durum wheat yield variables and grain quality (protein content). Five treatments (control treatment—T1, biostimulants—T2, slow-release urea—T3, biostimulants plus slow-release urea—T4, Mg and micronutrients—T5) were tested in a field experiment conducted over 3 seasons in the south of Spain; all were dosed at 120 kg N ha−1. The number of spikes increased significantly with biostimulant treatments in the first season (up to 33%, T2 and T4), while the highest significant grain yields were obtained with biostimulants applied individually in the first season (29.5%-T2) and biostimulants in combination with slow-release urea the second season (27.3%-T4), related to T1. Grain protein concentration was influenced by the treatment only in the second season, the driest during the study, when it was increased with biostimulants up to 4.2% with T2 in comparison with T1. Total protein production increased (28.1%T2) in the first season, (8.1–21.9% for T2–T4) in the second season and (6.5% T4) in the third season, when biostimulants were applied alone or in combination with slow-release urea, respectively. In general, plants treated with Mg and micronutrients produced a lower number of spikes, less yield, and reduced total protein compared to those doses with biostimulants. The application of amino acids as biostimulants was demonstrated to enhance durum wheat yield and total protein production and could be a potential tool for promoting nitrogen use efficiency in semi-arid areas.