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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 4, Num. 2, 1996, pp. 249-255
African Crop Science Journal
Vol.5. No.2, pp.249-255 1997

Evaluation of Leucaena leucocephala leaf prunings as a source of nitrogen for maize

P. L. Mafongoya, D. N. Mugendi^1 and C.G.S. Pedreira^2

Agronomy Institute, Box CY 550, Causeway, Harare, Zimbabwe ^1 Kenya Forstry Research School of Forest Resources and Conservation, University of Florida, Gainesville FL 32611, USA
^2 Department of Agronomy, University of Florida, Gainesville FL 32611, USA

(Received 14 February, 1995; accepted 6 June, 1996)


Code Number: CS96063
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ABSTRACT

Prunings of leucaena [Leucaena leucocephala (Lam.) De Wit] have long been regarded as a useful alternative to N fertilizer, but N use efficiency by crops is often low. The potential exists to synchronise nutrient release with crop nutrient demand through variation in the rate and placement of prunings. A 2x2x3 factorial experiment was conducted to evaluate the potential of leaves of leucaena to supply N to maize (Zea mays L.) plants grown in pots of soil (Grossarenic Paleudult) under glasshouse conditions. Factors tested were two rates of application (3 and 6 Mg ha^-1), two methods of placement (surface vs incorporation), and 3 levels of N fertilizer (0, 50, and 150 kg ha^-1 equivalent of urea in solution form). Surface applied prunings significantly increased maize shoot dry weight with increasing levels of N fertilizer. Although incorporation of prunings increased maize shoot dry weight, the incorporated treatments did not show any significant response to N fertilizer, indicative of adequate N supply from prunings. Both shoot and total dry weight significantly increased with increasing rates of prunings applied. Nitrogen recovery was increased by applying prunings together with N fertilizer. There was a higher N recovery with incorporation compared to surface application. Prunings applied at a rate of 3 Mg ha^-1 gave higher %N recovery than 6 Mg ha^-1. At the final harvest date, application of 6 Mg ha^-1 of prunings produced taller plants than 3 Mg ha^-1.

Key Words: Nitrogen use efficiency, placement methods, rates, leucaena prunings

RESUME

Les emondes de leucaena (Leucaena leucocephala (Lam.) De Wit) ont longtemps ete considerees comme une alternative aux engrais azotes, mais l'utilisation efficace de N par les plantes est souvent limitee. Il existe le potentiel synchroniser la liberation des substances nutritives avec la demande des nutritifs par une variation du nombre et du placement des emondes. Une experience factorielle (2x2x3) a ete effectuee pour evaluer le potentiel des feuilles de leucaena de fournir de lte aux plantes de mas (Zea mays L.) eleves en pots de terre (Grossarenic Paleudult) en conditions de serres. Les facteurs examines etaient les suivants: taux dlication (3 et 6 Mgha^-1), deux methodes de placement (surface vs incorporation), et trois niveaux de fertilisation dte (0,50 et 150 kg ha^-1) equivalent de en forme de solution. Les emondes appliquees la surface font augmenter d'une facon significative le poids sec des pousses de mas avec des niveaux plus eleves drais azotes. Lorporation des emondes augmente le poids sec des pousses de mas, mais il n pas de reponse significante avec les engrais azotes; ceci indique que sous cette forme dlication, les emondes fournissent de lazote d'une facon efficace. Le poids sec des pousses et le poids sec total augmentaient avec des taux plus eleves dndes. La recuperation dte augmentait par une application simultanee dndes et drais azote. La recuperation dte etait plus importante quand les emondes incorporees etaient comparees avec une application la surface. 3 Mg ha^-1 dndes appliquees donnaient une plus grande recuperation (%) dte que 6 Mg ha^-1. Au moment de la recolte, 6 Mg ha^-1 dndes appliquees produisaient des plantes de plus hautes tailles que 3 Mgha^-1.

Mots Cles: Licacite de lge dte, methodes de placement, taux, emondes de leucaena

INTRODUCTION

In most developing countries, nitrogen fertilizer is expensive and unavailable to smallholder farmers. This is mainly due to lack of foreign currency and developed infrastructure for distribution to small scale farmers.

In smallholder farming systems of the tropics, increasing use is being made of leguminous tree prunings as a source of nutrients for crop growth, particularly nitrogen. In alley cropping systems, arable crops are grown between rows of trees (Kang et al., 1984). The trees are pruned regularly to provide leaf prunings to the interplanted crop. In other instances, leaf material is harvested from trees growing outside the cropping area and transported to the crop field (Jeyaraman et al., 1989).

Leucaena [Leucaena leucocephala (Lam.) De Wit] has been widely used in this context particularly in alley cropping (Kang et al., 1981, 1984). A problem with the use of prunings, however, is low yield of the arable crop and low N recovery from the applied leaf prunings. Previous research results suggest that the rate of prunings applied and the method of placement have potential to increase the nitrogen use efficiency (Kang et al., 1984; Read et al., 1985).

Surface application of prunings can delay decomposition of materials and has been shown to reduce effectiveness when applied at planting as compared to incorporation (Wilson et al., 1986). Reduced tillage which is similar to applying prunings on the surface (mulch), has been shown to increase concentrations of carbon and nitrogen in the top 7.5 cm surface soil layer (Doran, 1980). Increased levels of carbon, nitrogen and water in the soil result in greater microbial activity. Enhanced microbial activity increases short term immobilisation and long term mineralisation of organic nitrogen. Nitrogen immobilised in microbial tissue can potentially be mineralised later in the growing season (Doran, 1980). Surface application of mulches may result in increased microbial biomass and enhanced immobilisation of organic N and applied fertilizer nitrogen. Incorporation of prunings has been shown to be more effective due to better mineralisation of organic N (Wilson et al., 1986). Incorporation of prunings also, may reduce nitrogen volatilisation losses as shown by Kang and Mulongoy (1992). They observed that broadcasted surface-applied leucaena prunings lost more N through volatilisation than incorporated prunings. Incorporation of 10 Mg ha^-1 of prunings of leucaena resulted in a higher maize (Zea mays L.) grain yield than surface application (Kang and Duguma, 1985). However, there have been conflicting results on methods of pruning application and nitrogen recovery by the associated crop. These results are from a range of different multipurpose tree species used, varied climatic zones and amount of prunings applied. Thus there is a need to define these relationships under glasshouse conditions before large-scale field trials are attempted.

The objective of the experiment was to determine the effect of rate and method of prunings application of L. leucocephala prunings and rate of urea-N fertilizer on maize growth, and N recovery by the maize plants during their early development.

MATERIALS AND METHODS

A glasshouse experiment was conducted from January to April 1993 at the University of Florida in Gainesville. Treatments were applied in a randomised complete block design with three replications, and consisted of combinations of two rates of leucaena leaf prunings (3 and 6 Mg ha^-1), two methods of prunings application (on the surface or incorporated into the top 5 cm of soil) and three rates of N fertilizer applied as topdressing (0, 50, and 150 kg N ha^-1 as urea). A control treatment was also included where no fertilizer or prunings were applied. Leucaena leaf prunings (containing 5.6% N) were collected from an established leucaena stand from the forage garden at the University of Florida. Prunings were dried at 60 oC to constant weight then applied to pots (5.3 and 10.6 g equivalent to 3 and 6 Mg ha^-1) filled with 2 kg soil (Arredondo fine sand, Grossarenic Paleudult, Loamy, Siliceous, Hyperthermic; pH (H2O)=6.5, CEC=7.71, %C=0.93) a day before planting. Maize was sown at five seeds pot-1 on 25 January. Urea-N was applied in solution (100 and 300 mg N equivalent to 50 and 150 kg N ha^- 1) on 8 February and pots were thinned to 2 plants on 11 February. Each pot was watered to soil field capacity (15% moisture by weight) approximately every 5 days.

Starting on 20 February, plant height was measured every 2 weeks. On 2 April all plants were harvested after the height measurements were taken. In each pot the two plants were cut at the soil surface and collected into a cloth bag. Pots were dumped upside down and the roots were separated, washed and also collected into cloth bags. The soil from the pot was homogenised and mixed with the remaining prunings before a subsample was taken for analysis.

Shoots and roots were oven dried to constant weight at 60 C. After weights were recorded all the shoots and roots were ground in a Wiley mill to pass through a 1-mm screen. Ground samples were analysed for N by micro-Kjeldahl digestion using a modification of the aluminum block digestion procedure (Gallaher et al., 1975; Hambleton, 1977). Equivalent plant sample weights to those used for N analysis were also oven-dried for 24 hours at 105oC so that N concentration may be calculated on a dry matter (DM) basis. The soil subsamples from each pot were air dried for 5 days and analysed for total N by micro-Kjeldahl digestion.

Nitrogen recovery by shoots was calculated as:

         N shoot content (treatment_ - N shoot (control)*100
% NREC = ----------------------------------------------------  
                Total N applied to treatment       

Height measurements, dry weight, tissue and soil nitrogen, and N recovery were subjected to ANOVA in the three-factor analysis. The control treatment was not included in the ANOVA for the three-factor analysis for the reason that the design would not have been balanced. A t-test was however, conducted to compare the control treatment with all the other treatments.

RESULTS

There were no significant three-way interactions for all the factors considered in this investigation.

Height. Plant height measured at 26, 40, 54, and 68 days after planting (DAP) was affected by different factors depending on plant age. At 26 DAP no significant effect of treatments (P < 0.05) was detected but at 40 DAP an interaction between pruning application rate (PR) and pruning application method (MA) was observed (Table 1).

Plants that received 3 Mg ha^-1 of prunings were taller (P < 0.05) when it was surface applied whereas for the 6 Mg ha^-1 rate MA did not influence height at 40 DAP. At 54 DAP, plant height responded only to urea-N (UN) rates. Plants that received no UN averaged 45.8 cm and were significantly shorter (P < 0.05) than plants where UN was applied at 150 kg N ha^-1 (50.3 cm). However, the response to 50 kg N ha^-1 (47.1 cm) was not different from that of 150 kg N ha^-1 (50.3 cm). On the final harvest date, height of plants at 68 DAP was affected by both PR and by the UN-by-MA interaction. Application of 6 Mg ha^- 1 of prunings resulted in significantly (P <0.05) taller plants (72.8 cm) than 3 Mg ha^-1 (68.3 cm). Surface application together with 150 kg N ha^-1 of UN produced significantly taller plants than both the 0 and 50 kg N ha^-1 treatments (Table 2).

Incorporation of prunings with UN did not significantly affect plant height. However, the method of prunings application was influential only when UN rates were 0 and 50 N kg ha^-1 (Table 2).

Dry weight. The dry weight of roots was not significantly (P < 0.05) affected by treatments at 68 DAP (data not shown). Applying 6 Mg ha^-1 prunings significantly increased shoot dry weight to 9.5 g from 1.3 g for the control and to 8.1 g for 3 Mg ha^-1. In pots where prunings were surface applied as mulch, 150 kg N ha^-1 of urea increased the dry weight of shoots by 91% (from 5.5 to 10.5 g) (Table 3). In the incorporated treatments, there was no significant response to N fertilizer.

The total dry weight (shoots plus roots) of maize plants at 68 DAP was affected by the rate of prunings application and the amount of urea-N fertilizer supplied (significant two-way interaction). Increasing PR from 0 to 3 and to 6 Mg ha^-1 significantly increased total dry weight of plants from 2.3 to 13.3, to 17.3 g, respectively, (P < 0.05). The response to 150 kg N ha^-1 urea (16.8 g) was not significantly different (P < 0.05) from that of 50 kg N ha^-1 (17.1 g), although both 50 and 150 kg N ha^-1 treatments were superior to 0 kg N ha^-1 (12.0 g).

Nitrogen in tissues and soil and N recovery. The % N concentration in shoots was affected by PR and UN only (but not by MA), whereas concentration in roots was only influenced by MA. Incorporating prunings increased N concentration in roots by 31% (0.64 vs 0.84% N) compared to surface application. Higher % N concentration in shoots corresponded to higher PR and higher UN. As PR was increased from 0 to 3, and to 6 Mg ha^-1, % N concentration in shoots significantly increased from 0.73 to 1.17, and to 1.4%, respectively. Treatments that received UN showed a higher % N concentration than the no-UN treatments, and 150 kg UN ha^-1 treatment was superior (P < 0.05) to 50 kg UN ha^-1 (Table 4). Total N concentration in the soil, which averaged 0.1 %, was not affected by treatments (P < 0.05). The lower prunings application rate gave significantly higher % N recovery in the maize shoots (20 vs. 16.3% N). Nitrogen recovery increased with increased UN applied, though no significant difference (P < 0.05) existed between 50 and 150 kg N ha^-1 (Table 5). Method of prunings application also affected N recovery in that the % N recovered was significantly higher with incorporation (22.2) compared to surface application (14.1) (P < 0.05).

DISCUSSION

Incorporation of prunings increased shoot dry weight but had no effect on total dry weight of maize plants. The lack of effect of method of prunings application on total maize dry weight conflicts with the results of Gutteridge (1992). In his work incorporation of prunings gave better dry matter yields than surface application. Read et al. (1985) also found that leucaena prunings incorporation increased dry matter yield of maize grown in the glasshouse relative to surface application. However, no differences between application methods were found under field conditions. Interaction between mulch application method and nitrogen levels on shoot dry weight agrees with results of Kang et al. (1981) and Wilson et al. (1986). Incorporation is known to increase rate of decomposition and enhance mineralisation of N which makes it more readily available to the plant (Read et al., 1985; Wilson et al., 1986; Gutteridge, 1992). Surface application of the mulch may have delayed decomposition, increased microbial activity and immobilisation of N by microbial population (Doran, 1980; Power and Doran, 1988). There was substantial fungal growth on treatments with surface application. This may have led to increased N immobilisation during the early part of the season hence limited N availability at lower levels of N application. However, with incorporation, N immobilisation seemed not to have occurred and hence a higher dry weight of maize shoots with incorporation in conjunction with lower rates of UN (0 and 50 kg ha^-1) application and also an overall increased N concentration in the roots with incorporation. Higher prunings application rate (6 Mg ha^-1) had a greater effect on all response variables measured except N recovery. This agrees with work of Kang et al. (1981), Read et al. (1985) and Gutteridge (1992) and may be attributed to higher amounts of N supplied by mineralisation of prunings at a higher rate. This is supported by the observation that mulch applied with 150 kg N ha^-1 had a higher shoot N content comared to 0 and 50 kg ha^-1. At the lower levels of N application nitrogen must have been limiting as plants showed a high degree of chlorosis. Incorporation enhanced N recovery probably because of faster mineralisation (Read et al., 1985).

Incorporation increased maize N recovery. This contradicts work of Varco et al. (1989) and Xu et al. (1993) who found no differences between surface and incorporation in field microplots. The N recovery values observed in our study are much higher than those found by Gutteridge (1992). This difference could be explained by the fact that Gutteridge used prunings alone without addition of inorganic N fertilizer. In this study inorganic N fertilizer was added with prunings which resulted in higher N recovery values. Mulongoy and van der Meersch (1988) and Xu et al. (1993) reported low recovery values, in the range of 4.0-9.8%. They postulated that, the rest of the nitrogen (not recovered) could have remained in the soil or was lost by denitrification. The loss of N by denitrification may also have been a factor in this study although denitrification was not measured. Factors which could have favoured denitrification were waterlogging in the pots (which did not have drainage holes), adequate supply of nitrate nitrogen, and high available soluble carbon from the prunings. Some prunings remained undecomposed at the end of the experiment (surface applied), an indication that some N may have been left in the prunings. This may serve to explain why the % N recovery for surface applied prunings were lower than with incorporation. Nitrogen in the form of ammonia may also have been lost through volatilisation from the surface applied prunings. This area needs further research.

The results of this study have shown that prunings applied in conjunction with inorganic N fertilizer will increase N recovered by maize crop. In addition, it became evident that prunings alone could not have provided the maize with adequate supply of N (except when incorporated in high quantities). Further research is needed in order to trace the fate of N applied with legume mulches, perhaps with aid of 15N labeling. To achieve better synchrony, % N recovery could perhaps be increased by split application of the prunings and also by mixing prunings of different qualities. Future research in this area is recommended under field conditions.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the following people who helped in the successful implementation of this project. Professor J. B. Sartain and his staff in the Soil Fertility Laboratory who provided resources and valuable guidance to this work. Dr. J. E. Moore and his staff in the Animal Nutrition Laboratory for chemical analysis, Steve Linda of IFAS Statistics and Gregory MacDonald for statistical advice.

REFERENCES

Doran, J.W. 1980. Soil microbial and biochemical changes associated with reduced tillage. Soil Science Society of America Journal 44:765-771.

Gallaher, R.N., Weldon, C.O. and Futral, J.G. 1975. An aluminum block digester for plant and soil analysis. Soil Science Society of America Proceedings 39:803-806.

Gutteridge, R.C. 1992. Evaluation of the leaf of a range of tree legumes as a source of nitrogen for crop growth. Experimental Agriculture 28:195-202.

Hambleton, L.G. 1977. Semiautomated method for simultaneous determination of phosphorus, calcium, and crude protein in animal feeds. Journal of the Association of Official Analytical Chemists 60:845-852.

Jeyaraman, S., Punishothaman, S. and Govindaswamy, M. 1989. Leucaena as a substitute for nitrogen fertilizer in lowland rice. Leucaena Research Report 10:24-25.

Kang, B.T. and Duguma, B. 1985. Nitrogen management in alley cropping systems. In: Nitrogen Management in Farming Systems in Humid and Subhumid Tropics. Kang, B.T. and Van der Heide, J. (Eds.), pp. 269-284. Institute of Soil Fertility, Haren, The Netherlands.

Kang, B.T. and Mulongoy, K. 1992. Nitrogen contribution of woody legumes in alley cropping systems. In: Biological Nitrogen Fixation and Sustainability of Tropical Agriculture. Mulongoy, K., Gyeye, M. and Spencer, D.S.C. (Eds.), pp. 367-375. Wiley-Sayce Co-Publication, IITA, Ibadan, Nigeria.

Kang, B.T., Wilson, G.F. and Lawson, T.L. 1984. Alley Cropping: A Stable Alternative to Shifting Cultivation. IITA, Ibadan, Nigeria. pp. 22.

Kang, B.T., Sipens, L. ,Wilson, G.F. and Nangju, D. 1981. Leucaena [Leucaena leucocephala (Lam) de Wit] prunings as nitrogen source for maize (Zea mays L.). Fertilizer Research 2:279-287.

Kang, B.T., Wilson, G.F. and Sipkens, L. 1981. Alley cropping maize and Leucaena leucocephala in Nigeria. Plant and Soil 63:165-179.

Mulongoy, K. and van der Meersch, M.K. 1988. Nitrogen contribution by leucaena (Leucaena leucocephala) prunings to maize in an alley cropping system. Biology and Fertility of Soils 6:282-285.

Power, J.F. and Doran, J.W. 1988. Role of crop residue management in nitrogen cycling and use. In: Cropping Strategies for Efficient Use of Water and Water Conservation. ASA Spec. Publications No. 54. Hargrove, W.L. (Ed.), pp.101-113. ASA, CSSA, and SSSA. Madison, W.I.

Read, M.D., Kang, B.T. and Wilson, F.F. 1985. Use of Leucaena leucocephala leaves as source of nitrogen for crop production. Fertilizer Research 8:107-117.

Varco, J.J., Frye, W.W., Smith, M.S. and MacKown, C.T. 1989. Tillage effects on Nitrogen recovery by corn from a nitrogen-15 labeled legume cover crop. Soil Science Society of America Journal 53:822-827.

Wilson, G.F., Kang, B.T. and Mulongoy, K. 1986. Alley cropping: trees as sources of green-manure and mulch in the tropics. Biological Agriculture and Horticulture 3:251-267.

Xu, Z.H., Myers, R.J.K., Saffigna, P.G. and Chapman, A.L. 1993. Nitrogen cycling in leucaena (Leucaena leucocephala) alley cropping in semi-arid tropics. I. Mineralization of nitrogen from leucaena residues. Plant and Soil 148:63-72

Xu, Z.H., Myers, R.J.K., Saffigna, P.G. and Chapman, A.L. 1993. Nitrogen cycling in leucaena(Leucaena leucocephala) alley cropping in semi-arid tropics. II. Response of maize growth to addition of nitrogen fertilizer and plant residues. Plant and Soil 148:73-82.

Copyright 1996 The African Crop Science Society


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