The characteristics of nitrate nitrogen leaching in soil under different irrigation levels were studied by soil column simulation experiment with numerical simulation done using LEACHM model taking nitrate nitrogen leaching under different irrigation levels as the research background. In sandy soils, an irrigation amount of 300 mm would cause nitrate nitrogen to leach downward 75~150 cm, with a leaching amount of 10~30.7 kg/ha; and an irrigation amount of 700 mm would make nitrate nitrogen leach downward about 3.5 m, with a leaching amount of 98 kg/ha. Research data showed that the amount of nitrate nitrogen leaching was positively correlated with the irrigation intensity level, irrigation level directly determined the amount of nitrate nitrogen leaching, and influenced its leaching depth.

Five rates of urea-N each at two water levels (0.6 & 1.0 ETc) were applied to three varieties (Butte, Carmel, and NonPareil) of almonds [Prunus dulcis (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 >1500 kg·ha–1 in 1984 and as high as 3800 kg·ha–1 during the 12-year period for the 1.0 ETc water treatment and optimum N rate. Nitrogen response was generally in the 600–1000 kg·ha–1 range, with water treatment response in the 200–500 kg·ha–1 range. The three varieties generally responded to higher N and water rates in the order Butte > Carmel > NonPareil. Leaf analyses (three to six each year) were used to monitor treatment effects and evaluate need for other nutrients.