Saturday, 15 July 2006

Plant Nitrogen Recovery from an Enriched 15N-Manure.

Hector Mario Quiroga - Garza1, Jose Antonio Cueto - Wong1, and William C. Lindemann2. (1) INIFAP Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias, Blvd. Jose S. Valdez 1200 Pte., Matamoros, Coahuila, 27440, Mexico, (2) NMSU Dept of Agronomy and Horticulture, P.O. Box 30003, Las Cruces, NM 88003-8003

The “Comarca Lagunera”, located at Mexico's arid North Central region, is one of the most important dairy production zones. The dairy cow concentration produces an estimate of 800,000 Mg manure yr-1 (dry basis). With the objective of estimate the N recovery efficiency from manure and fertilizer applied in mixture to annual forage crops, a study was established at “La Laguna” Research Station of INIFAP. During the 2001 spring season, a sudan grass was established on two plots, one of the plots was fertilized with a commercial Ammonium Sulfate (AS), and the second plot with the same, but labeled AS fertilizer (5% atom 15N). The hay produced in one harvest, from both plots was used to feed a dairy Holstein cow, first the normal forage by a 10 d period and then, the enriched forage (0.73% atom15N) for the following 10 d. On each period, manure produced during the first three days was discarded, then collected during the following seven days. The manure was stored for three months, the average manure N content ranged between 1.7 to 2%, and the labeled manure had 0.53% atom 15N. The dry manure was applied to PVC pots (15 cm diameter and 50 cm height) filled with soil. Three annual forage crops were planted in the pots, ryegrass (fall-winter 2001-02), sudan grass (spring-summer 2002), and ryegrass (fall-winter 2002-03). Four manure doses were evaluated: 0, 30, 60, and 120 Mg ha-1, one application, and combined with AS doses: 0, 120, and 240 kg N ha-1; the fertilizer was applied on each growing season. When the enriched manure was used, a no-labeled fertilized was applied, when a normal manure was used, a labeled (10% atom 15N) fertilized was applied. Pots were irrigated without leaching. After each crop ended, soil was removed from the pot, mixed with roots and stalk left by the previous crop. The highest manure N recovery was found at the 30 Mg ha-1, with 9% removed by the three crops aerial dry matter production: 5, 3 and 1% on each crop, respectively. At the highest manure doses 120 Mg ha-1, N recovery dropped to a half, 5%. 15Nitrogen recovered from the soil + roots + stalk mixture after the third crop were 87% and 84%, for the 30 and 120 Mg ha-1 manure doses, respectively. By a difference, unaccounted 15N were 4% and 11% for the same manure doses, respectively. The fertilizer did not affect the N recovery from manure. From the fertilizer, 15N recovery by the three crops aerial dry matter was 22% for the 120 kg N ha-1, increasing significantly to 25% for the 240 kg N ha-1 doses, these values were not affected by the manure doses. Recovery of 15N from the soil + root + stalk at the end of the third crop was 39 and 41%, respectively. By a difference, unaccounted 15N from the fertilizer were 39 and 34%, respectively. Nitrogen from a fertilizer is used by the crop almost immediately after it is applied to the soil; however its losses by volatilization may be high. Nitrogen from manure, is released at very low rates, with much lower crop use than fertilizers, but it increase the soil N reservoirs reducing at minimum the N gas losses.

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