Long-term Effects of Nitrogen and Drip Irrigation Water Levels on Almond Yields

Abstract

<jats:p>Five rates of urea-N each at two water levels (0.6 &amp; 1.0 ET<jats:sub>c</jats:sub>) were applied to three varieties (Butte, Carmel, and NonPareil) of almonds [<jats:italic>Prunus dulcis</jats:italic> (Mil) D. A. Webb] planted in 1981 on a 3.65 × 5.47-m spacing (550 trees/ha) on Arbuckle gravelly loam (Fine-loamy, mixed, thermic Typic Haploxeralf). Trees were drip-irrigated to basins (three per tree) ≈7 cm deep and 30 cm in diameter, located 76 and 183 cm on either side of the trees in the tree row. N rates ranged from 0–57, 0–198, 0–454, 113–907, 170–1361, 227–1814, 227–1814, 170–1361, 113–907, 113–907, 113–907, 0–907, 0–907 and 0–907 g per tree, respectively, during 1982–1995 and were applied on a monthly basis in four to six increments beginning in April. Almond meat yields were &gt;1500 kg·ha<jats:sup>–1</jats:sup> in 1984 and as high as 3800 kg·ha<jats:sup>–1</jats:sup> during the 12-year period for the 1.0 ET<jats:sub>c</jats:sub> water treatment and optimum N rate. Nitrogen response was generally in the 600–1000 kg·ha<jats:sup>–1</jats:sup> range, with water treatment response in the 200–500 kg·ha<jats:sup>–1</jats:sup> range. The three varieties generally responded to higher N and water rates in the order Butte &gt; Carmel &gt; NonPareil. Leaf analyses (three to six each year) were used to monitor treatment effects and evaluate need for other nutrients.</jats:p>