Correlations between biomass productivity and soil and plant tissue nutrient concentrations for Leucaena leucocephala (K-8) growing on calcareous soils

Forest Ecology and Management, 18 (1987) 241-250

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Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Correlations between Biomass Productivity and Soil a n d P l a n t T i s s u e N u t r i e n t C o n c e n t r a t i o n s for Leucaena leucocephala (K-8 ) G r o w i n g on Calcareous Soils E.L. GLUMAC, PETER FELKER and I. REYES

Centre for Semi-Arid Forest Resources, Caesar Kleberg Wildlife Research Institute, College of Agriculture and Home Economics, Campus Box 218, Texas A & I University, Kingsville, TX 78363 (U.S.A.) (Accepted 18 March 1986)

ABSTRACT Glumac, E.L., Felker, P. and Reyes, I., 1987. Correlations between biomass productivity and soil and plant tissue nutrient concentrations for Leucaena leucocephala (K-8) growing on calcareous soils. For. Ecol. Manage., 18: 241-250. The woody legume Leucaena leucocephala (K-8) is useful for fuel and forage production in the sub-tropics and tropics. When planted on favorable sites L. leucocephala (K-8) has produced 22 Mg dry biomass ha 1. However, many investigators have observed that leucaena productivity is site-specific, growing best on well-drained and fertile soils. L. leucocephala (K-8) was planted on calcareous soils in 1982 at a site in Kingsville, TX. Biomass productivity ranged from 1.4 to 10 Mg ha ~which was attributed to soil variability. Foliar macro- and micronutrient analyses were conducted for ten elements and soil phosphorus and pH were measured. Leaf P was found to be positively correlated with biomass production {r=0.71, p=0.002) as was leaf Mg (r=0.57, p=0.022). Leaf Ca (r=0.55, p=0.028) and Fe (r=O.56, p=O.024) were negatively correlated with biomass. The soil pH at 15-30 cm (r = 0.60, p = 0.013) and 30-60 cm (r = 0.88, p = 0.0001 ) depths was negatively correlated with biomass. Sodium bicarbonate-extractable P was not correlated with the leaf P or any other variables while 1:10 water-extractable P was positively correlated with Fe and soil pH at 30-60 cm. We postulate that the lack of correlation between sodium bicarbonate-extractable P and leaf P may be due to iron-calcium co-precipitation of soil P.

INTRODUCTION The rapid-growing, nitrogen fixing genus Leucaena has attracted considerable attention in the last ten years in the tropics and sub-tropics (National R e s e a r c h C o u n c i l , 1984). T h e h i g h e s t yields of Leucaena are a s s o c i a t e d w i t h r a i n f a l l g r e a t e r t h a n 1000 a n d less t h a n 3 0 0 0 m m ( N a t i o n a l R e s e a r c h C o u n c i l , 1984). Takahashi and Ripperton (1949) reported leucaena's best growth

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© 1987 Elsevier Science Publishers B.V.

242 occurred between 650 and 1900 mm in Hawaii. The maximum growth of Leucaena, especially the "Hawaiian Giants" obtained from Central America is highly dependent on soil type (National Research Council, 1984). Leucaena's intolerance for acid and water-logged soils is well documented (Takahashi and Ripperton, 1949; Brewbaker and Hutton, 1979; Hutton, 1983). Leucaena's highest yields ( 22 Mg h a - 1) are on fertile, neutral to slightly alkaline and well drained soils in the lowland tropics ( Oakes, 1968; Brewbaker and Hutton, 1979). Correlations of macro- and micronutrients in Leucaena with growth would be helpful in establishing critical nutrient levels for Leucaena. Unfortunately, little data of this kind exists in the literature. Because of leucaena's nitrogenfixation ability, there does not seem to be a deficiency of N for its growth when properly inoculated with rhizobia. The most critical element for maximum growth of this plant may be phosphorus in both acid and calcareous soils (Benge, 1977; Hegde, 1983). Singh and Mudgal (1967) analyzed L. leucocephala foliage each month for a period of one year and found the mean P and Ca contents to be 0.27 and 1.47%, respectively. Other studies have found P to be 0.23% (National Research Council, 1977) and 0.22% (D'Mello and Taplin, 1978) and Ca to be 2.4 and 1.9% respectively. Data on micronutrients for Leucaena are even more limited than for the macronutrients. D'Mello and Taplin found the following levels in leucaena leaf meal (/zg g - i ): Cu, 11; Fe, 907; Zn, 19; and Mn, 51. Reyes (1983) conducted a greenhouse study with three levels of lime and micronutrients and found that optimum growth was obtained with the following leaf levels: P, 0.16%; K, 1.5%; Mg, 0.18%; Na, 0.001%; Ca, 0.76%; Fe, 59/~g g-i; Zn, 22/lg g-i; Mn, 95 #g g-i; Cu, 2/~g g-i; and soil pH, 5.1. A leucaena biomass productivity study was begun at Texas A&I University in March 1982 with L. leucocephala (K-8). The location of the study was in Kingsville, TX (27 ° 32'N) where the mean annual rainfall is about 750 mm. As in many semi-arid environments there is considerable year-to-year variation in the annual rainfall. Limited fertilizer (liquid ammonium phosphate, 10-34-0, 176 kg ha-1 at time of planting) and non-irrigated conditions were imposed and no consideration for soil type was given. As with biomass production of Prosopis spp. (Felker et al., 1983 ), adequate growth on marginal soils and with limited inputs is deemed necessary due to their low availability in arid and semi-arid regions. METHODS

Experimental Design The design of the experiment consisted of 16 blocks of L. leucocephala (K8). Each block consisted of a 7 X 7 array with trees planted on a 1.5 X 1.5 m spacing. Biomass measurements excluded the outer row and were only made

243 on the inner 25 trees. Treatments consisted of harvest schedules, i.e., four blocks were to be harvested each year to 4 years until all blocks were harvested. However, as described elsewhere (Glumac et al., 1986), severe freezes precluded this harvest schedule. During the course of this study a seven-fold range in production was observed between the 16 blocks. Therefore, foliar and soil analyses were conducted for each plot and the results examined statistically for correlations with growth to determine the factors limiting growth.

Biomass Determination Survival and yields are reported in a companion paper ( Glumac et al., 1986). Four blocks were harvested with a chainsaw at ground level one year after planting in April 1983. All 16 blocks were harvested in February 1984 (after a - 12 °C freeze in December 1983 ) and in December 1984. The woody biomass productivity for the December 1984 harvest ranged from 1.4 Mg h a - 1 for block 16 to 10 Mg h a - 1 for block 14. A correlation analysis was conducted to determine any relationships between leaf and soil parameters with the December 1984 harvest.

Plant Tissue Analysis Leaf samples were collected on 5 July, 1984 during the middle of the growing season from each of the 16 blocks in the study. Five trees were chosen from the NE, NW, SE, SW corners and middle of the inner 25 trees of each of the 16 blocks for a total of 80 samples. The mean of these five determinations was used in correlations to biomass productivity. Twelve fully expanded leaves were taken from each tree, beginning about 15 cm from the apical meristem. The leaves were collected in paper bags, dried at 50 ° C for 2 weeks, and ground in a stainless steel Wiley Mill with a 40-mesh screen. The dried samples were placed in an oven at 70 ° C for 24 hours before being weighed for digestion. H a l f a gram of the dried material was used in the nitric acid digestion procedure of Havlin and Soltanpour (1980). The elements K, Mg, Ca, Na, Cu, Mn, and Zn were analyzed by atomic absorption spectrophotometry using an Perkin Elmer Model 290B atomic absorption spectrophotometer while iron was analyzed by a Varian Model 1475 A.A.S. Phosphorus was analyzed using a phosphomolybdate reduction with ascorbic acid ( M u r p h y and Riley, 1962). Nitrogen was determined by a modified colorimetric nitrogen assay (Cline et al., 1986).

Soil Analysis Three randomly located holes were dug in the interior of each of the 16 blocks. Soil samples were taken from 0-15 cm, 15-30 cm, and 30-60 cm depths. These soil samples were composited to form a single sample per depth per block,

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placed in muslin soil sample bags, and air-dried in the laboratory. Subsamples were taken at the time of sampling for gravimetric moisture determinations. Soil pH was determined with a 0.01 M CaC12 solution (McLean, 1982). Sodium bicarbonate extractable P ('Olsen-P') and water extractable P of a 1:10 water extract were determined as described by Olsen and Sommers (1982).

Site Description Two soil-profile pits dug in March 1985 (one adjacent to blocks 6 & 7 and the other adjacent to blocks 14 & 15) confirmed the existence of two soil series. Willacy fine sandy loam (fine-loamy, mixed, hyperthermic udic Argiustoll) underlay all of block 14 and parts of neighboring blocks 11, 13, and 15. Miguel fine sandy loam ( fine, mixed, hyperthermic udic Paleustalf) underlay the rest of the blocks with the exception of block 16 and part of block 9 which were located on Orelia fine sandy loam (fine-loamy, mixed, hyperthermic typic Ochraqualf). Although a profile was not taken, this soil type is associated with the Miguel soil (USDA, 1965) and is abundant around the study area. The lighter surface color and poor surface drainage of the Orelia soil could be seen in the field, especially after a heavy rain. Dominant features of the Miguel and Orelia soils are poor internal drainage and a higher clay content (USDA, 1965 ).

Statistical Analysis The correlation procedure of SAS (SAS, 1982) was used to detect significant correlations between the 19 variables involved in this study. RESULTS

The leaf tissue and soil parameters that were significantly correlated with biomass are presented for each of the 16 blocks in Table 1. In addition, the parameters significantly correlated with biomass are listed with their associated significant correlations in Table 2. One of the first observations that can be made is that the block (14) with the highest dry woody biomass (10 Mg ha -1 ) also had the highest leaf P (0.185%), highest leaf Mg (0.277%), lowest iron (88/~g g - l ) and lowest soil pH (6.5) at the 30-60 cm depth. The fact that the 16 blocks were not located on the same soil type was only casually observed in the beginning of the biomass production study. However, it became apparent after the second harvest in December 1984 that block 14 was producing 3-4 times the average of the other 15 blocks. Also, the border effect was not so apparent in this block, i.e., trees in the border row of block 14 were not noticeably larger than the trees in the interior of the block. Biomass was negatively correlated with Ca, Fe, and the soil pH at 15-30 and

245 TABLE 1 Leaf tissue and soil parameters that were significantly correlated with wood dry biomass yield Block

14 11 13 4 15 9 8 6 5 1 10 3 7 2 12 16

Yield ( Mg ha 1)

10.05 5.73 4.85 3.54 3.40 3.25 3.16 2.96 2.67 2.57 2.52 2.52 2.09 2.04 1.80 1.41

Leaf nutrient levels ( n = 5 )

Soil ( n = 3 )

P (%)

Ca (%)

Mg (%)

Fe (#g g-l)

pH2

pH3

0.185 0.157 0.180 0.138 0.161 0.148 0.148 0.139 0.134 0.152 0.150 0.128 0.136 0.145 0.150 0.154

0.98 1.02 0.87 1.34 1.12 1.13 1.34 1.09 1.14 1.28 1.09 1.21 1.21 1.21 1.18 1.15

0.277 0.219 0.220 0.252 0.214 0.206 0.213 0.244 0.240 0.246 0.221 0.222 0.231 0.217 0.230 0.205

88 91 95 97 93 99 105 102 112 113 106 119 109 106 98 93

6.6 6.0 6.9 7.0 6.4 7.4 7.8 7.7 7.4 7.6 7.0 7.5 7.6 7.1 7.6 7.4

6.5 7.5 8.1 8.0 7.7 8.3 8.3 8.0 8.1 8.2 8.0 8.1 8.0 8.1 8.1 8.1

Blocks ranked according to yield from harvest on 6 December 1984 in descending order, pH2 = soil pH at 15-30 cm, pH3 =soil pH at 30-60 cm. 3 0 - 6 0 c m depths. T h e c o r r e l a t i o n of N w i t h b i o m a s s was n o t s i g n i f i c a n t (r = 0.47, p = 0.068). N was significantly c o r r e l a t e d with P ( r = 0.80, p = 0.0001 ) a n d n e g a t i v e l y c o r r e l a t e d w i t h Ca (r= - 0 . 6 5 , p = 0 . 0 0 6 ) a n d Fe ( r = - 0 . 6 8 , p = 0.004). T h i s suggests t h a t with i n c r e a s i n g availability of P in t h e less calc a r e o u s a n d l o w e r - p H soil, t h e p l a n t is able to m a n u f a c t u r e m o r e p r o t e i n a n d produce more biomass. T h e r e l a t i o n s h i p s b e t w e e n soil P p a r a m e t e r s a n d b i o m a s s p r o d u c t i v i t y in this s t u d y were inconclusive. T h e s o d i u m b i c a r b o n a t e - e x t r a c t a b l e O l s e n - P was n o t s i g n i f i c a n t l y c o r r e l a t e d w i t h leaf P at a n y of t h e t h r e e d e p t h s or w i t h a n y of t h e o t h e r 16 variables used in this study. T h e w a t e r - e x t r a c t a b l e P for t h e 3 0 - 6 0 c m d e p t h was n e g a t i v e l y a s s o c i a t e d w i t h leaf P, a l t h o u g h n o t significantly. I t was p o s i t i v e l y c o r r e l a t e d w i t h Fe a n d soil p H at t h e 3 0 - 6 0 c m depth. DISCUSSION O f t h e six p a r a m e t e r s s i g n i f i c a n t l y c o r r e l a t e d w i t h b i o m a s s ( T a b l e 2), p H at t h e 3 0 - 6 0 c m d e p t h a n d leaf P were t h e m o s t significant. T h e fact t h a t leaf P was s i g n i f i c a n t l y c o r r e l a t e d w i t h yield is n o t surprising, c o n s i d e r i n g t h e P d e m a n d c r e a t e d b y N - f i x i n g p l a n t s ( L a r u e a n d P a t t e r s o n , 1981). Field trials

246 TABLE 2

Summary of significant correlations between leaf and soil parameters and dry woody biomass (yield) Parameters/yield

Leaf parameters

1. Biomass

2. P

P

Yd 0.71 (.002)

3. Ca

4. Mg

5. Fe

Yd - 0.56 (.024)

6. pH2

7. pH3

Yd -0.88 (.000)

0.71 (.002) Zn 0.61 (.011 ) Yd - 0.55 (.028) Yd 0.57 (.022) Ca 0.50 (.046) Yd -0.60 (.013) P -0.61 (.013)

Soil parameters Ca -0.55 (.028) Ca -0.68 (.004) Zn - 0.69 (.003)

Mg 0.57 (.022) Cu 0.58 {.019) Fe 0.50 (.045)

Fe -0.56 (.024) Fe -0.72 (.002) N - 0.65 (.006)

Cu - 0.63 (.009) P -0.55 (.026) Ca -0.48 (.060)

K - 0.50 (.150) Ca 0.54 (.030) Mg -0.60 (.013)

N - 0.68 (.004) Fe 0.63 (.009) Cu -0.51 (.050)

N 0.80 (.000)

P

pH2 -0.60 (.013) pH2 -0.55 (.026) pH2 0.54 (.030)

0.63 (.009)

pH2 0.56 (.025)

Fe 0.56 (.025)

pH2 0.64 (.008)

pH3 -0.88 (.000) pH3 -0.61 (.013) pH3 0.48 (.060) pH3 0.60 (.013) pH3 0.57 (.022) pH3 0.64 (.008)

WP3 0.57 (.022) WP3 0.51 (.044) WP3 0.50 (.050)

Correlation coefficients (r) are beneath the parameter and the p values are given in parentheses ( n = 16). Yd = biomass, pH2 = soil pH at 15-30 cm, pH3 = soil pH at 30-60 cm, WP3 = water-extracted P at 30-60 cm.

have demonstrated that leucaena productivity is responsive to P fertilization ( Takahashi and Ripperton, 1949; Hegde, 1983 ). Magnesium was also significnantly correlated with yield and with pH at the 30-60 cm depth but was not correlated with any other variables. Since P is a factor limiting biomass production in legumes, it is important to understand the relationships between P and other nutrient variables such as Ca, Fe, and soil pH. In calcareous soils P-fixation is with calcium carbonates (Adams, 1980) so P is expected to be less available to the plant at higher concentrations of Ca and at a higher pH. The maximum availability of P is in a pH range between 6.0 and 7.0 (Bohn et al., 1979), thus the significant correlations between leaf Ca, P, and soil pH are to be expected. The negative correlation of biomass with Fe may be due to P precipitation onto Fe oxides present in the soil. Iron and A1 have long been associated with P-fixation in acid soils (Bohn et al., 1979), however their roles in calcareous soils have not been clearly defined. The fixation of P in calcareous soils is described as being governed by a reaction of P with solid phase CaCO3 (Adams, 1980). There have been some problems associated with the reaction mechanisms by which this fixation occurs. The availability of P in calcareous soils may be affected by other factors such as inorganic phosphate particle size and

247 surface area, reactive surface area of calcite, soil particle size, the plant species, and the root environment (Hawkins and Kunze, 1965; Ryan et al., 1985). Holford and Mattingly (1975) examined P sorption on limestone and concluded that the large quantity of P sorbed onto the limestone was not due entirely to adsorption to CaCO3. They suggested that the rapid precipitation of P observed may have been due to Na dithionite Fe soluble impurities in the limestone to the amount of 3350/~g g- 1. In a study of calcareous Lebanese soils, Ryan et al. (1985) concluded that Fe oxides, especially the more reactive forms, have a dominant influence on P reactions in calcareous soils. The Fe in their study was the citrate-dithionitebicarbonate (CDB) or total 'free' Fe. The Fe oxides appear to be directly involved in sorption of P. Phosphorus release or desorption in these soils may be difficult. A study was carried out on four Texas soils in the early 1960's (Hawkins and Kunze, 1965 ) in which the soils were fractionated into P components by various extracting procedures. In a Victoria clay at the 64-97 cm depth they found 56/~g Ca-P g-l, 54 ~g A1-P g-l, 2.6/~g Fe-P g-l, 82/~g of reductant soluble Fe g-1 and 204/~g occluded Fe-A1 g-1. The Olsen-available P was 0.9 #g g- 1. The high concentration Of reductant soluble Fe ( determined by a sodium citrate-Na dithionite extraction) is significant because this is the same form of iron that Holford and Mattingly (1975) believed was precipitating P onto Ca carbonates. They found this form of Fe to increase with depth. Given the previous demonstations of P co-precipitation by Ca and Fe in calcareous soils ( Holford and Mattingly, 1975; Ryan et al., 1985 ) and the negative correlation of P and biomass with Fe and Ca, we suggest that P co-precipitation by Ca and Fe is the major soil factor limiting leucaena's growth in this study. Furthermore the nearly identical alpha values and correlation coefficients between leaf Fe and leaf Ca with leaf P and biomass are suggestive of a mechanism involving stoichiometric co-precipitation of P by Fe and Ca. For soil P measurements to be useful or meaningful a high positive correlation must occur between either plant productivity or percent P in the tissue and some measure of soil P ( Kamprath and Watson, 1980 ). Two measures of soil P are the P removed by various chemical extractants and P in the equilibrium soil solution. These forms of P may be characterized as a more physicallysorbed P (labile P) and chemisorbed P, removed by chemical extractants (Ryden and Syers, 1977). A better evaluation of physically-sorbed P may be obtained with 2 distilled water extractions than with the Olsen extraction ( Ryden and Syers, 1977). This may be due to the lower ionic strength of the extractant. Luscombe et al. (1979) observed a negative correlation with percentage yield increase of ryegrass (Loliumperenne) and water-extractable P. The correlation obtained with the water extraction was better than with the Olsen extraction; it was not explained why the negative relationship was obtained.

248

Ojala et al. (1983) found that for predicting mycorrhizal dependency, a 1:10 soil water extract gave a better correlation than the Olsen bicarbonate method. The water extract is measuring the intensity of P supply solution whereas the bicarbonate method measures the capacity factor. Correlations of crop yield with plant tissue and soil nutrients have been used for many years in plant testing laboratories ( Smith, 1962). Although the results of correlation analysis cannot be given as proof of an essential element deficiency, they serve as guides for the grower or researcher. There are many factors influencing the growth of a plant and it is usually not possible to adequately address all factors. Soil drainage has been demonstrated to be a major factor affecting productivity of leucaena (Oakes, 1968). Given that the productivity of leucaena was lowered on the poorly drained Miguel soil series, aeration problems may also be influencing leucaena production in this study. While Fe-P and reductant soluble-P are not considered important in well aerated soils, they have been found important in poorly drained soils and perhaps could be a problem on the Miguel soil series (Reddy and Patrick, 1983 ). The results presented in this study indicate that it may be necessary to add P to the soil to obtain greater production on the Miguel and Orelia soils. Bharatiya Agro-Industries Foundation (BAIF) in India recommends the annual application of single superph~sphate (50-100 kg h a - 1) for leucaena crops under intensive forage production (Hegde, 1983). Annual phosphate fertilization should be examined on the Miguel and Orelia soils. For leucaena on acid soils, a high positive correlation exists between pH and biomass ( Hutton, 1983 ). A significant negative correlation was found between pH and biomass on a calcareous soil. In both cases, P is probably limiting because of its narrow pH availability range. Block 14 which had 10 Mg of biomass h a - ' had a pH of 6.6 (15-30 cm ) and 6.5 ( 30-60 cm). Most of the blocks had pH values from 7.0 to 8.3 at these depths. The soil profiles removed indicated that calcium carbonate deposits began at about a 50-cm depth in the Miguel soil, but did not begin until about 150 cm in the Willacy soil. CONCLUSIONS

The strongest correlations with biomass were leaf P and soil pH at 30-60 cm. Leaf P and leaf Mg were positively correlated with biomass. The percentage of P found in the leucaena leaves ranged from 0.185 to 0.128. Leaf Ca and Fe were negatively correlated with biomass. Soil pH at 15-30 and 30-60 cm was negatively correlated with biomass. Soil pH values at the 30-60 cm depth ranged from 6.5 to 8.3. We suggest that the limiting factor for L. leucocephala (K-8) on a moderately drained and near-neutral soil such as a Willacy series may be the amount of rainfall received. However, on poorly drained soils with high pH, P may not

249 be a v a i l a b l e in t h e a m o u n t s n e e d e d for m a x i m u m p r o d u c t i o n . P h o s p h o r u s defic i e n c y m a y be c a u s e d b y p r e c i p i t a t i o n o f P o n t o Fe oxides w h i c h are p r e s e n t in m a n y c a l c a r e o u s soils. N o c o r r e l a t i o n s w e r e f o u n d w i t h O l s e n ' s soil P. Soil p H a t 3 0 - 6 0 c m a n d l e a f Fe w e r e f o u n d to be p o s i t i v e l y c o r r e l a t e d w i t h a 1:10 w a t e r e x t r a c t a b l e soil P; h o w e v e r t h i s m e a s u r e o f soil P w a s n o t c o r r e l a t e d w i t h l e a f P. R e s e a r c h is n e e d e d to d e t e r m i n e a s o i l - P e x t r a c t i o n t e c h n i q u e t h a t is well c o r r e l a t e d w i t h leucaena biomass production and leaf tissue P concentration under alkaline conditions. ACKNOWLEDGEMENTS T h e f i n a n c i a l a s s i s t a n c e o f t h e U.S. D e p a r t m e n t of E n e r g y ( S u b c o n t r a c t No. 1 9 X - 0 9 0 6 6 C w i t h O a k R i d g e N a t i o n a l L a b o r a t o r y u n d e r M a r t i n M a r i e t t a E n e r g y S y s t e m s , Inc. c o n t r a c t D E - A C 0 5 - 8 4 0 R 2 1 4 0 0 ) , t h e C a e s a r K l e b e r g Wildlife R e s e a r c h I n s t i t u t e a n d t h e A g e n c y for I n t e r n a t i o n a l D e v e l o p m e n t is g r a t e f u l l y a c k n o w l e d g e d . W e t h a n k Dr. R.L. B i n g h a m for h e l p w i t h t h e s t a t i s tical a n a l y s e s .

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