Irrigated Alfalfa Response to Phosphorus and Potassium in a Calcareous Soil

Abstract

The response of alfalfa (Medicago sativa L.) to phosphorus (P) and potassium (K) fertilizer often varies with soil type, the initial soil test P and K levels, irrigation and harvest management, and yield level. The objectives of this study were to determine the response of irrigated alfalfa to P and K fertilizer on a Wetherill loam soil in southwestern Colorado and to assess the impact on soil test P and K levels. Four P (0, 37, 74, and 148 kg ha 21 ) by three K (0, 93, and 186 kg ha 21 ) rates were applied to newly seeded alfalfa in the fall of 1995. An additional 37 kg P ha 21 was applied annually to half of each plot in the spring of 1997, 1998, and 1999. Potassium fertilizer increased alfalfa dry matter (DM) yield significantly in 1996 only. Alfalfa K uptake averaged 311 kg ha 21 yr 21 in 1997-1999. Soil test K level at the 0-to 30-cm depth was not impacted by K fertilization and remained above the critical level throughout the duration of the study. On the basis of these and other research results, a response to K fertilization is unlikely on most alfalfa-producing soils in Colorado because of their high K-buffering capacity. The initial application of 37 -148 kg P ha 21 did not affect alfalfa DM production signifi37 kg P ha 21 yr 21 when no P was applied initially. Both the initial and annual P fertilizer applications increased alfalfa P concentration significantly in 1997 through 1999. Alfalfa P uptake averaged 32.6 kg ha 21 yr 21 . Similarly, the initial and/or annual P application 1213 increased soil ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA) extractable P significantly in 1998 through 2000. When no P was applied, soil test P level at the 0-to 15-cm depth dropped from 8.3 mg kg 21 at the initiation of the study in August 1995 to less than 1.0 mg kg 21 at study termination in April 2000. It took a total of approximately 150 kg P ha 21 to raise soil test P to its initial level after 4 years of production. More than 260 kg P ha 21 would have been required to raise soil test P level to where a response to P fertilization would not be expected. Alfalfa yield response to P fertilizer was small even when soil test P level dropped to well below the critical level. No yield advantage was observed to maintaining soil test P above the critical level. Although not conclusive, our results indicate that annual P fertilizer applications are superior to one-time applications on our calcareous soils. More research is needed to refine P fertilizer recommendations and soil test correlation relationships for irrigated alfalfa hay production in southwestern Colorado.

Alfalfa Yield Components and Soil Potassium Depletion as Affected by Potassium Fertilization

“…1). As frequently reported, alfalfa yields depend on the K e content of the soils (Kafkafi et al, 1977; Havlin et al, 1984; Berrada and Westfall, 2005).…”

“…In the irrigated areas of the Ebro valley (Spain), the normal K e contents for a good crop are considered to be between 125 and 250 mg kg −1 , whereas levels below 125 mg kg −1 are considered low (Piñeiro et al, 2010). According to Berrada and Westfall (2005), the response of alfalfa to K and P often varies with growing conditions, soil type, initial soil test K and P levels, irrigation, harvest management, and yield level. Havlin et al (1984), in Colorado, reported that when soil test K levels remained high, no K fertilization was necessary unless there would be a direct economic benefit from improved alfalfa forage quality.…”

Phosphorus uptake during four years by different vegetative cover types in a riparian buffer

“…These values would yield an annual removal of P on the order of 9.9 kg ha -1 in a single harvest. Phosphorus concentrations over a 3-year period in irrigated pure alfalfa stands have been reported by Berrada and Westfall (2005) to average 2.4 g kg -1 for a range in P additions. Marino and Berardo (2005) found a 4-year, cumulative removal of P by alfalfa, to total 61 kg ha -1 without any direct addition of P. This is approximately three times the amount removed in the alfalfa cover type over a similar time frame, but it should be noted that the alfalfa cover type in the current study was strongly dominated by smooth brome by the 4th year of the study.…”

Producción de alfalfa (Medicago Sativa L.) cultivada con riego sub-superficial y diferentes niveles de fósforo

“…Phosphorus (P) is one of the nutrients that have a major inf luence on the growth of alfalfa because of its need in different biochemical functions of the plant and, its deficiency reduces the amount and quality of forage (Picone et al, 2003;Mikkelsen, 2004). Alfalfa shows significant response to increased application rates of P (Berrada and Westfall, 2005). This nutrient is added to the soil in a single application at the beginning of the cycle, regardless of the irrigation system used and the number of cuts made in alfalfa forage (Karagić et al, 2008).…”