Recamán-Serna, Edgar A.

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    Utilización de urea líquida (ULB-35®) en producción de forrajes en Puerto Rico.
    (2009) Recamán-Serna, Edgar A.; Sotomayor-Ramírez, David; College of Agricultural Sciences; Martínez, Gustavo; Pérez Alegría, Luis R.; Department of Crops and Agro-Environmental Sciences; Kolterman, Duane A.
    Four experiments were conducted on commercial farms, to quantify forage yields and nutritional contents of pastures used for hay with the application of liquid urea (ULB-35®). Liquid material was applied through the center pivot irrigation system (Lajas-1), travelling sprinklers (Sabana Grande and Lajas-2) or by aerial fertilization equipment (Arecibo). In Lajas- 1, the total dry matter (DM) yield (6 months) was highest for 15-5-10 (N-P2O5-K2O) complete fertilizer (168 kg N/ha), followed by the middle (74.7 kg N/ha), high (112 kg N/ha) and low (37.3 kg N/ha) levels of ULB-35®, with 10,429, 7,158, 5,776 and 4,534 kg MS/ha, respectively. In Sabana Grande, DM forage yield differences at 6 months were not found between ULB-35® (9,743 kg DM/ha) and 15-5-10 complete fertilizer (9,078 kg DM/ha) when both were applied at 112 and 84 kg N/ha, respectively, but both treatments were higher than ammonium sulfate (6,666 kg DM/ha) applied at 84 kg N/ha. In Arecibo, differences were not found for forage yields, protein and nitrogen-use efficiency, after applying 56 kg N/ha/application as ammonium sulfate and three concentrations of ULB-35® (7.5, 3.0 and 1.5 % N). However, ULB-35® was 50 % more economical than ammonium sulfate. In Lajas-2, differences were not found for forage yield and protein, between treatments ULB-35® (112 kg N/ha/application), ammonium sulfate and granular urea (when both were applied to 56 and 112 kg N/ha/application). However, nitrogen- use efficiency was 90 % higher for low levels (56 kg N/ha), than with high levels (112 kg N/ha). A quantitative relationship between chlorophyll meter SPAD-502® and N concentration in forage tissue was developed. To complement the agronomic studies, four experimental NH3-N volatilization assays were performed (in laboratory and field conditions). The rate of volatilization increased with the soil pH (5.43 to 6.45), decreased with time (80.8 % of volatilization occurred during the first seven days), and was higher for granular urea, in relation to other nitrogen sources (ULB-35® and ammonium sulfate). Ammonium volatilization with ULB-35® was similar to ammonium sulfate and, in most cases, these did not differ from the control treatment (without N). Volatilization was 9.0% of the 75 kg N/ha applied. The use of the urease inhibitor Agrotain® reduces NH3-N volatilization from ULB-35® by 54.0%.