Alfalfa dry matter yield, nutritional status and

International journal of Agronomy and Plant Production. Vol., 4 (3), 389-398, 2013 Available online at http:// www.ijappjournal.com ISSN 2051-1914 ©2013 VictorQuest Publications

Alfalfa dry matter yield, nutritional status and economic analysis of potassium fertilizer doses and frequency 1,3

1

2

Alberto C. de Campos Bernardi , Joaquim B. Rassini , Fernando Campos Mendonça , Reinaldo de 1,3 Paula Ferreira 1- Embrapa Pecuária Sudeste. São Carlos – SP. 2- Dep. Engenharia de Biossistemas – ESALQ/USP. Priacicaba - SP. 3-Bolsista do CNPq; *Corresponding Author: Alberto C. de Campos Bernardi

Abstract The objective of this study was to evaluate the effect of different doses and application frequencies of potassium fertilizer on the alfalfa dry matter yield and on the potassium content in the plant and in the soil. The experiment was carried out in a Typic Hapludox -1 soil. The use of 1,420 kg.ha per year of K2O applied after two cuttings (6 applications -1 per year) increased the alfalfa dry matter yield until 30,500 kg ha , and provided the best use of K at the higher doses of fertilizer. Total K removal of Alfalfa shoot reached 704 kg -1 -1 ha per year of K2O with the application of 1,623 kg ha per year of K2O. At the end of the experiment, the soil exchangeable K increased with K rates and the differences were observed until 0.6 m of depth. Keywords: Medicago sativa, nutritional status, soil testing, potassium use efficiency, profitability. Introduction

An adequate supply of nutrients is important for alfalfa production and is essential to maintain high forage quality and profitable yields (Moreira et al., 2008). Potassium fertilization is essential for alfalfa production (Rassini and Freitas, 1998) and is the most common nutrient input for this crop in the high weathered, low-fertile and acid soils of the tropical region. High-yielding alfalfa removes large amounts of potassium from the soil in each cut (Smith, 1975; Lanyon and Smith, 1988). Lloveras et al. (2001) found -1 -1 extractions from 1500 to 1700 kg ha (with productivity of 21.5 t.ha DM) in soil of high fertility. Therefore, adequate potassium nutrition enhances stand longevity (Smith, 1975; Berg et al., 2005). Well established pastures properly managed and fertilized are the most practical and the main source of food for cattle, as well as the source with the least cost for cattle feeding (Camargo et al., 2002). On dairy production systems, the intensive pasture grazing allows to increase stocking rates and the productivity (Corsi and Nussio, 1992; Primavesi et al, 1999). Among the controllable factors determining forage yield and quality, the soil fertility is one of the most important, including the fertilizer treatment. Tropical acid soils are naturally poor in plant nutrients, therefore, soil liming and balanced nutrient supply essential to ensure high yields and high forage quality (Corsi and Nussio, 1992; Primavesi et al, 1999; Camargo et al., 2002). However, fertilization may represent as much as 27% of the total production cost of alfalfa in typical Brazilian systems for intensive dairy cattle production (Vinholis et al., 2008). So, an adequate assessment of the fertilizer investment is critical. Therefore, economic studies on alfalfa fertilization on dairy production systems are required for establishing conditions under which the economic return may be maximized, especially with pastures on acid and low fertility soils. Hence, the effects of various management practices and related issues become important factors for achieving a profitable dairy production. The objective of this study was to evaluate the effect of doses and frequency of application of potassium fertilizer on the alfalfa dry matter yield and potassium content in plant and soil, and also to

Intl. J. Agron. Plant. Prod. Vol., 4 (3), 389-398, 2013

estimate the net profit of the system. Material and Methods A two-year growing seasons field study was carried out at Embrapa Cattle Southeast, in Sao Carlos o o (22 01’ S and 47 54’ W; 856 m above sea level), State of Sao Paulo, Brazil. The climate is a humid subtropical climate (Köppen climate classification type Cwa), with yearly average of low and high temperatures of 16.3 and 23.0°C, respectively, and a total precipitation of 1502 mm, falling mostly during spring and summer seasons (CEPAGRI, 2010). Soil type was a Typic Hapludox (Calderano Filho et al., 1998), with the following chemical properties in the 0-0.2, 0.2-0.4 and 0.4-0.6m layers: pHCaCl2 = 5.9, 5.3 and -3 -3 -3 5.1; organic matter = 21, 11 and 10 g.dm ; Presine = 42, 10 and 3 mg.dm ; K = 1.3, 0.9 and 0.5 mmolc.dm ; -3 -3 -3 Ca = 29, 14 and 11 mmolc.dm ; Mg = 13, 5 and 2 mmolc.dm ; CEC = 69, 50 and 48 mmolc.dm ; and basis -1 saturation = 63, 39 and 28%; and the physical characteristics: sand = 730, 710 and 689 g kg ; clay = 253, -1 -1 273 and 302 g kg ; and silt = 17, 17 and 9 g kg . Irrigated alfalfa (Medicago sativa cv. Crioula) was sown in May 2005 with a planting density of 20 kg -1 ha of seeds inoculated with Sinorhizobium meliloti. Dolomite lime was applied to increase the basis -1 saturation at 80% before planting. Plots were fertilized uniformly at the planting with 120 kg ha P2O5 (single superphosphate) and 30 kg of FTE BR-12 (1.8% of B, 0.8% Cu, 3% Fe, 2% Mn, 0.1% Mo, 9% Zn). The soil liming, the phosphorus and the micronutrients fertilization were repeated whenever the soil chemical analysis 2 indicated a fertility decrease. The experiment was carried out in 3.2-m plots, each one formed by eight sowing 2-m length rows, with a 0.2-m interlinear space. The experimental design was a randomized blocks in 4x4 factorial, with three replications. The treatments comprised four levels of potassium applications in topdressing fertilization (0, 50, 100 and 150 kg -1 ha of K2O), as KCl (60% K2O), and 4 potassium application frequencies (12 = after each cutting, 6 = after two cuttings, 4 = after three cuttings; and 2 = two applications per year, one in the autumn-winter season and one in the spring-summer season). The amount of potassium fertilizer applied at each treatment was always the same, independently of the frequency, so that the total quantities supplied at each crop cycle were 600, -1 1200 and 1800 kg ha of K2O. Alfalfa shoot dry matter yield was periodically determined when the crop was with 10% of flowering, harvesting a minimum of six rows with 1-m length per plot on 25 growing seasons. The alfalfa samples were dried at 65°C for 72 h, for determining the dry matter yield, and then were ground. Total potassium, calcium and magnesium concentrations in shoot samples were determined after hot nitric-percloric digestion, and determined by flame photometry (K) and atomic absorption spectrophotometry (Ca, Mg), according to Nogueira et al. (2005). After 25 alfalfa forage cuttings, soil samples were collected at 0-0.2, 0.2-0.4 and 0.40.6m-depth for determining the soil exchangeable K. The potassium use efficiency (KUE), the agronomic efficiency (AE), the crop recovery efficiency (RE), and the physiological efficiency (PE) of applied potassium chloride (KCl) were computed, using the following formulae based on Dobermann (2007): -1 KUE = YK FK (kg of harvest product per kg of K2O applied), -1 AE = (YK – Y0) FK (kg of yield increase per kg of K2O applied), -1 RE = (UK – U0) FK (kg of increase in K2O uptake per kg of K2O applied), -1 PE = (YK – Y0) (UK – U0) (kg of yield increase per kg of increase in K2O uptake from fertilizer), Wherein: -1 FK = amount of K-fertilizer applied (kg ha ); -1 YK = crop yield with applied K (kg ha ); -1 Y0 = crop yield (kg ha ) in a control treatment with no K; -1 UK = total plant K uptake in aboveground biomass at maturity (kg ha ) in a plot that received K; -1 U0 = total K uptake in aboveground biomass at maturity (kg ha ) in a plot that received no K. The data of alfalfa dry matter yield and the shoot concentrations of potassium, calcium and magnesium, the potassium in aboveground biomass and the exchangeable K in soil were tested to detect significant statistical differences among the treatments, and the response surfaces and equations were adjusted as a function of the treatments. Whenever it was appropriate, the Tukey test was used for identifying the best treatments. The results obtained for alfalfa dry matter yield due to the potassium fertilizer treatments were used to simulate pasture stocking rate, the milk production, the production cost, and the achieved net profit. The methodology for cost estimation was based on an electronic spreadsheet drawn up by Vinholis et al. (2008) for evaluating Brazilian intensive dairy cattle production systems, where the forage diet of the cows consisted on pasture alfalfa, Cynodon spp. cv Tifton 85, and sugarcane provided during the autumn-winter season (dry season of the year).

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The following data were used in the simulation: a) average cow live weight (LW) = 550 kg; b) cow dry -1 matter (DM) consumption = 3.05% of the LW, corresponding to 16.8 kg day of DM; c) the alfalfa pasture grazing represented 14% of the total of cow dietary consumption, and 20% of the forage consumption (Vinholis et al., 2008). The estimation of the stocking rate and the milk production was made using the following equations: i) Stocking rate -1 SR = (DM GE) (AGN GI DIFC) Wherein -1 SR = stocking rate in the alfalfa pasture, animal ha -1 DM = dry matter yield, kg ha GE = grazing efficiency (GE = 0.7) AGN = annual number of grazing events (12 grazing events/year) GI = grazing interval, days (30 days) DIFC = daily individual forage consumption, kg of dry matter/cow/day ii) Milk production -1 MP = (365 SR MY) [1+(TPIA + SCIA) SR] Wherein -1 -1 MP = annual milk production, liters ha year -1 -1 -1 MY = daily milk yield, liters cow day (20 liter cow , 4% fat content) -1 -1 TPIA =tropical pasture individual area, ha cow (TPIA = 0.125 ha cow ) -1 -1 SCIA = sugarcane individual area, ha cow (SCIA = 0.043 ha cow ) P.S.: TPIA a/nd SCIA are the areas of tropical pasture and sugarcane used for feeding the cows that also graze in 1 ha of alfalfa. iii) Milk cost production -1 MCP = TCP MP Wherein: -1 MCP = milk cost production, US$ L -1 -1 TPC = total production cost of milk, US$ ha year -1 -1 MP = annual milk production, liters ha year iv) Net profit NP = GR - MCP Wherein: -1 NP = net profit, US$ L -1 GR = gross revenue, US$ L -1 MCP = milk cost production, US$ L The net profit estimation was obtained by profit functions, considering four scenarios, composed by the combination of two cost levels for both milk and potassium, representing realistic price fluctuations (Table 1). The data were submitted to the statistical analysis of variance for detecting differences among treatments, and crop response functions to the potassium fertilizer were adjusted. Results and Discussion Dry matter yield of alfalfa at first and second growing season as a function of K fertilizer level and frequency of application is illustrated in Figure 1. The highest DM yields in both years (36,890 and 24,131 kg -1 -1 ha ) were obtained with 1,411 and 1,432 kg ha of K2O applied after two cuttings. These values are approximately 57 and 59% higher than those obtained without potassium fertilizer. Results are consistent with those observed by Smith (1975), Rassini and Freitas (1998), who found an increase in alfalfa DM yield as potassium fertilization increased. The yield increases in this study were higher than the increases reported by Kafkafi et al. (1977) and Lloveras et al. (2001). Rando and Silveira (1995) worked with potassium fertilization of alfalfa on the North region of the Parana State, under a Eutrudox soil, founding out an increase on the dry matter production in all the 8 cuts done. -1 The application of 150; 300; and 600 kg ha of K2O resulted on increases of 22%; 41%; and 45% on the -1 plant dry matter yield. The biggest estimated production (sum of 8 cuts) was reached with 500 kg ha of -1 -1 K2O. In the same work, the author stipulated a need of 132 kg ha of K2O for the first cut and 217 kg ha of K2O for the two first cuts, for reaching 90% of the maximum dry matter yield. The yield reduction from the first to the second year was greater on the lower levels of potassium -1 fertilization (Figure 1D). The lower reduction (33.5%) was obtained with 1,346 kg ha of K applied six times a

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year, one at each two cuttings. These results indicate that the adequate potassium supply increases the stand longevity, as shown by Smith (1975) and Berg et al. (2005). The large yield reduction between the years is the result of a natural decline induced by repeated crop cuts. Stand longevity of alfalfa has a major importance for farmers with irrigated stands. Alfalfa longevity is limited by the decline in plant population, which results from harvesting or inappropriate grazing management. Additionally, the decline is also brought about by diseases, presence of weeds, insect damages, fall in soil fertility, and a faster deterioration with irrigation (Rice et al., 1989). Longevity is limited and reaches no more than four-to-six years (Humphries et al., 2004). -1 -1 Maximum K concentrations in alfalfa shoots were 35.2 g kg , achieved with 1,610 kg ha of K2O -1 (Figure 2A). This is 58% higher than the control K concentration (20.4 g kg ). The increase in K -1 concentration (from 20.4 to 35.2 g kg ) with increasing K fertilization is similar to the results reported by Smith (1975) and Sheaffer et al. (1986) on soils responsive to K fertilization. They found out that the K tissue -1 -1 concentration increased from 8.9 to 20.5 g kg , when K fertilization rates increased from 0 to 448 kg ha , -1 -1 and from 11.4 to 25.3 g kg when K fertilization rates increased from 0 to 334 kg ha . The principle of foliar diagnosis is based on comparing nutrient concentrations in leaves with standard values. Crops are considered to integrate factors such as the presence and availability of soil K, weather variables, and crop management. So, plant tests are the best reflection of what the plant has taken up. The ranges of K, Ca and Mg levels considered adequate in Brazil in alfalfa shoot at the early flowering are (g kg 1 ): 20-35 for K, 10-25 for Ca and 3-8 for Mg (Werner et al., 1997). Thus, the potassium levels in alfalfa shoots -1 obtained in this work were considered adequate. The maximum potassium fertilization levels (1,800 kg ha ) -1 could lead to insufficient Mg concentration in shoot (< 3 g kg ). The effect of competition for absorption sites -1 in the plant was greater with Ca, since the lower levels of potassium fertilization (approximately 100 kg ha ) lead to inadequate Ca concentration in the shoot. On the other hand, these results could also indicate that Ca concentration in shoots were lower than the necessary to assure the best alfalfa performance. Plants draw nutrients into their roots by tapping the soil solution and creating a concentration gradient across their root membranes, and then, cationic nutrients compete for absorption into the plant via osmosis. Figure 2A also illustrates the result of this competition between K, Ca and Mg for alfalfa uptake, since increases in potassium fertilization supply lead to decreases on Ca and Mg concentrations in the shoots, as reported by Smith (1975), Lanyon and Smith (1988) and Lloveras et al. (2001). The relationship between nutrient concentration and crop yield forms the basis for the utilization of plant analysis to assess plant nutrient status. Dry matter production and shoot K levels showed a positive correlation (Figure 3B), where the yield increased together with the K concentration. Furthermore, alfalfa plants continue to absorb K even when available K exceeds the plant needs. This unique property of K plant uptake, called luxury consumption (Havlin et al., 1999), may be observed where great amounts of K (up to 36 -1 g kg of potassium in alfalfa shoot) were accumulate without any increase in crop yield. The total amount of K removed with the aboveground herbage increased with applied K and frequency -1 of application (Figure 3). Removal of K reached 704 kg ha per year of K2O with the application of 1623 kg -1 -1 ha per year of K2O, compared with 205 kg ha for the control treatment. Lloveras et al. (2001) found linear increases on potassium removal with increased K fertilization. The ratio of DM yield to the amount of applied K (KUE) and AE significantly declined with increasing K application rates (Table 2), as already shown by Dobermann (2007) for N applications. The highest yields were observed at lower levels of potassium supply. As the nutrient supply increases, the yield increase becomes smaller because yield determinants are other than potassium. Considering the frequency of application, there were no significant differences in KUE. Potassium use efficiency may be also called a productivity partial factor of applied K, which is an aggregate efficiency index that includes contributions to crop yield derived from the uptake of indigenous soil K, K fertilizer uptake efficiency, and conversion efficiency of K acquired by plants to DM yield. Agronomic efficiency is the product of the K recovery efficiency from applied K sources. Physiological efficiency is defined as the efficiency of the plant on using each unit of K come from applied K to produce biomass, and crop recovery efficiency represents the degree of congruence between plant K demand and available K supply from the applied fertilizer. However, the results obtained in this work also showed no statistical differences between treatments in PE and RE (Table 2). The highest levels of potassium fertilization increased both, surface and deep soil extractable potassium (Figure 4A). Alfalfa has a lower root density than most grasses, and generally a deeper rooting zone where soil moisture is available. Despite this deep root system, Peterson et al. (1983) reported that alfalfa absorbed K most heavily from the surface soil volume, compared to the Ap and deeper horizons. This finding supports the efficiency of the common practice of topdressing K fertilizer onto existing stands of alfalfa when needed. Although a survey of soil fertility and forage management specialists in the USA indicates that

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-1

additional K is rarely recommended when the concentration of exchangeable K is greater than 300 kg ha -1 (about 150 mg kg ) in the surface soil layer (Lanyon and Griffith, 1988). Soils with low cation exchange capacity (CEC) values generally do not have the ability to maintain a sufficient supply of K to the plants throughout the growing season without depleting the exchangeable soil K pool. This low CEC soils often lack the capacity to absorb sufficient K reserves to satisfy crop requirements along a growing season. Figure 4A confirm that, without adequate potassium fertilization (control), it was observed high depletion on the exchangeable soil K. Potassium leaching depends on the concentration of K in the soil solution, on the water amount moving through the soil, and on the soil ability to bind K (Havlin et al., 1999). Considering the high levels of potassium fertilizer used in this experiment, and the low ability of tropical soils to absorb and hold K (due to low CEC), a K movement in the soil profile was observed (Figure 4A) leading to values considered high by (> -3 3,0 mmolc.dm ) at 0.2-0.4m and 0.4-0.6m-depth. The stocking rate is a key management variable for determining productivity and profitability of grazing systems, since this index determines the quality and the forage use efficiency, the animal performance and the milk production per area (Fales et al., 1995). Plotting the estimated stocking rate of alfalfa pasture (Figure 5A), and the milk production (Figure 5B) against the rate of potassium fertilization showed, in both the cases, a quadratic relationship with maximum -1 values ranging around 1,500 and 1,380 kg ha per year of K2O, respectively. The potassium application increased the average stocking rate by approximately 30 percent, from 15 (zero K) to more than 20 animals -1 -1 per ha, and the milk production increased from 30,000 to 34,000 kg ha yr . Under good growth conditions, including a balanced nutrient supply for the alfalfa pasture, the stocking rates were improved due to increase on the DM yield. The results of this simulation have shown that an alfalfa pasture adequately supplied with potassium fertilizer support high stocking rates and results on a high milk production per hectare. Therefore, as shown by Fales et al. (1995), the optimal stocking rate for a given dairy farm depends on individual farm resources (e.g., land, buildings, cows, etc.), and can be adjusted to face these resources constraints and avoid or minimize significant adverse economic impacts. Fig. 2 (A to D) describes the polynomial regression curves of the net profit functions for dairy production according to levels of potassium fertilizer for the 1st and 2nd crop seasons, and the averages of the two growing seasons in the four studied scenarios of milk and potassium fertilizer prices. The profit was estimated as a function of income and expenses associated with maintenance and production of dairy cows during one year in a system described by Vinholis et al. (2008). Income and expenses were calculated by multiplying the actual requirements of various commodities with the low and high price scenarios. Estimated profit functions are useful in economic decisions for alfalfa fertilization, other than dry matter yield curves alone. The net profit ranged from 0.05 to 0.5 US$ per liter of milk. At the low milk price (US$ 0.278 per L), the profitability was low at less than US$ 0.2 per liter of milk (Figures 6A and 6B). The highest potassium price significantly reduced the net profit. In both scenarios (A & B), the maximum profit for K2O doses was -1 obtained with 1,212 kg ha for the lower potassium price potassium (US$ 0.833) and 1,045 kg/ha for the higher potassium prices potassium(US$ 1.667). Under the highest milk price (US$ 0.444 per L), the profitability improved and ranged from US$ 0.4 to 0.5, and it was not affected by changes in the potassium price (Figure 6C and 6D). The reason for this is the high agronomic response of alfalfa to the potassium supply, so that even with the additional cost of heavier potassium applications, the profitability of milk production is maintained, and it is more sensitive to the milk price than to the potassium fertilizer price. The results indicate that the variation in total net profit related to the milk price was greater than that related to the potassium fertilizer price. This is because the fertilizer represents 27% in the total milk production cost (Vinholis et al., 2008). Furthermore, the results showed that even with a scenario of high potassium fertilizer prices (B and D), this nutrient should not be neglected, due the clear positive effects on production. The input price has little influence on production costs, since the income associated with milk production is much more associated to the amount of milk produced than to the potassium fertilizer price. Under the studied price relationships scenarios, a profitable strategy for increasing productivity was the maintenance of a balanced fertilized. The results also indicated that an intensive dairy production with a adequate fertilization of alfalfa pastures and high stocking density can be a valuable strategy for dairy farmers to improve the net economic returns.

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Table 1. Scenarios for simulations with two price levels for both milk and potassium. Milk price USD per L Potassium price (USD per kg K2O) Scenario A 0.278 0.833 B 0.278 1.167 C 0.444 0.833 D 0.444 1.167

st

Figure 1. Alfalfa dry matter yield according to levels of potassium fertilizer and frequency of application at 1 nd nd st (A) and 2 (B) crops season, average of both growing season (C) and ratio of yield at 2 and 1 growing seasons (D).

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40

Dry matter yield (kg) ha

B

y = -46,268x2 + 3346,5x - 25905 R2 = 0,6522**

37500

-1

32 yK = -5E-06x2 + 0,0161x + 22,237

-1

Shoot levels (g ) kg

45000

A

Ca Mg K

R2 = 0,835***

24

2

yCa = 8E-07x - 0,003x + 10,325 R2 = 0,685**

16

yMg = 8E-07x2 - 0,0025x + 5,087 R2 = 0,572*

8

30000 22500 15000 7500 0

0 0

600

1200

10

1800

18

26

34

42

-1

-1

K levels in shoot (g kg )

K2O level (kg ha )

Figure 2. Alfalfa K, Ca and Mg levels in shoot according to levels of potassium fertilizer (A) and alfalfa dry matter yield as a function of K levels in shoot (B). Average of 2-yr growing season.

Figure 3. Alfalfa total K uptake in aboveground biomass according to levels of potassium fertilizer and frequency of application. Average of 2-yr growing season. Table 2. Alfalfa potassium use efficiency (KUE), agronomic efficiency (AE), crop recovery efficiency (RE) and physiological efficiency (PE) according to levels of potassium fertilizer and frequency of application. Average of 2-yr growing season. Frequency of application 2 4 6 12

600

KUE 1200

1800

40.0 a 46.7 a 38.3 a 41.2 a

21.0 b 19.2 b 21.9 ab 27.5 b

16.1 b 14.8 b 13.9 b 13.6 c

600

AE 1200

19.5 a 10.7 b 26.2 a 9.0 b 17.9 a 11.6 ab 20.7 a 15.2 ab

RE 1800 600 1200 (kg ha-1 of K2O) 9.3 b 0.27 0.21 8.0 b 0.34 a 0.25 b 7.1 b 0.35 0.24 6.7 b 0.39 a 0.21 ab

1800

600

PE 1200

1800

0.18 0.15 b 0.20 0.14b

82.6 82.2 60.8 55.6

51.0 33.6 51.3 72.3

54.6 52.3 34.9 49.8

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