Leucaena Prunings Research Articles

Effectiveness of calcined rock phosphate and leucaena prunings as a source of nutrients for maize in a tropical soil

Cost reduction and an increased efficiency in the utilization of nutrients are essential for establishing agricultural systems in the tropics. The combined effects of calcined Al phosphate (ALP) and leucaena prunings (L) on the agronomic efficiency and on the efficiency of physiological use of nitrogen (N) and phosphorus (P) in maize were assessed. The treatments consisted of 160 kg ha− 1 of P2O5 from ALP and 100 kg ha− 1 of N from urea (ALP+U); 160 kg ha− 1 of P2O5 from ALP and 6 Mg ha− 1 of L (ALP+L); 160 kg ha− 1 of P2O5 from single superphosphate (SSP) and 100 kg ha− 1 of N from U (SSP+U); 160 kg ha− 1 of P2O5 from SSP and 6 Mg ha− 1of L (SSP+L); and a control without fertilization. The decreasing order of effectiveness among treatments was SSP+L > ALP+L > SSP+U > ALP+U > control. Both leucaena–phosphate combinations had beneficial effects on the growth of the maize, the N and P recovery, and the agronomic efficiencies. Both ear weight and grain weight were higher under the SSP+L treatment than under the SSP+U treatment and higher under the ALP+L treatment than under the ALP+U treatment. The low N and P agronomic efficiency in maize grown under the ALP+U treatment made the combined use of these fertilizers undesirable. The satisfactory efficiency of grain production shown by the maize grown under ALP+L indicated that this treatment could replace processed fertilizers for use in agrosystems management in the tropics.

Moisture conservation and nitrogen recycling through legume mulching in rainfed maize (Zea mays)–wheat (Triticum aestivum) cropping system

Mulching with vegetative materials is a highly beneficial and widely-investigated agro-technique in rainfed areas but the adoption of this practice has been constrained due to non-availability of mulch biomass locally. Live mulching with fast-growing annual green manure legumes like sunnhemp (Crotalaria juncea) or prunings of Leucaena leucocephala grown as hedge rows can be done for moisture conservation as well as nutrient cycling in the maize–wheat cropping system, which is predominantly followed in the high rainfall sub-mountainous region of north-western India. A field experiment was conducted at Selakui, Dehradun during 2000–2004 to study the effect of legume mulching, viz. in situ grown sunnhemp and Leucaena prunings, along with varying N levels, viz. 0, 30, 60 and 90 kg N ha−1 (to maize), and 0, 40 and 80 kg N ha−1 (to wheat) on productivity, soil moisture conservation and soil physico-chemical properties. Intercropped sunnhemp added 0.75–1.45 t dry matter and 21.6–41.3 kg N ha−1 at 30–35 days, while Leucaena twigs added 1.89–4.15 t dry matter and 75.2–161.3 kg N ha−1 at 60–65 days of maize growth. Live mulching with sunnhemp or Leucaena biomass improved soil moisture content at maize harvest (+1.15–1.57%) and crop productivity by 6.8–8.8% over no mulching. Combined use of both the mulching materials was more effective in improving the soil moisture content (+2.08–2.29%) and grain yield (15.1%) over their single application. Response of maize to N fertilizer application was significant up to 90 kg N ha−1, and it was relatively more pronounced under the mulching treatments. Residual effect of mulching on wheat showed an increase in yield of 10.2% with sunnhemp or Leucaena, and 27.9% with sunnhemp + Leucaena. There was an improvement in organic C and total N status of soil, and a decrease in bulk density associated with an increase in infiltration rate due to mulching at the end of 4 cropping cycles. It was concluded that legume mulching is a highly beneficial practice for enhanced moisture and nutrient conservation, leading to increased productivity and soil health of maize–wheat cropping system under Doon valley conditions of north-western India.

Green leaf manuring with prunings of Leucaena leucocephala for nitrogen economy and improved productivity of maize (Zea mays)–wheat (Triticum aestivum) cropping system

Green leaf manuring with prunings of Leucaena leucocephala is regarded as a useful source of N to plants but the actual substitution of N fertilizer, release and recovery of N as well as effects on soil fertility are not adequately studied. The present studies investigated the effect of sole and combined use of Leucaena prunings and urea N fertilizer in different proportions on productivity, profitability, N uptake and balance in maize (Zea mays)–wheat (Triticum aestivum) cropping system at New Delhi during 2002–2003 and 2003–2004. Varying quantities of Leucaena green leaf biomass containing 3.83–4.25% N (18.2–20.5 C:N ratio) were applied to provide 0, 25, 50, 75 and 100% of recommended N (120 kg ha−1) to both maize and wheat before sowing. In general, direct application of urea N increased the productivity of both crops more than Leucaena green leaf manure, but the reverse was true for the residual effect of these sources. The productivity of maize increased progressively with increasing proportions of N through urea fertilizer and was 2.41–2.52 t ha−1 with 60 kg N ha−1 each applied through Leucaena and urea, which was at par with that obtained with 120 kg N ha−1 through urea alone (2.56–2.74 t ha−1). Similarly, wheat yield was also near maximum (4.46–5.11 t ha−1) when equal amounts of N were substituted through Leucaena and urea. Residual effects were obtained on the following crops and were significant when greater quantity of N (>50%) was substituted through Leucaena. Nitrogen uptake and recovery were also maximum with urea N alone, and N recovery was higher in maize (33.4–42.1%) than in wheat (27.3–29.8%). However, recovery of residual N in the following crop was more from Leucaena N alone (8.5–10.3%) than from urea fertilizer (1.7–3.8%). Residual soil fertility in terms of organic C and KMnO4 oxidizable N showed improvement with addition of Leucaena prunings, which led to a positive N balance at the end of second cropping cycle. Net returns were considerably higher with wheat than with maize, and were comparatively lower with greater proportion of Leucaena because of its higher cost. Nonetheless, it was beneficial to apply Leucaena and urea on equal N basis for higher productivity and sustainability of this cereal-based cropping system.

Evaluation of the effect of hedgerow intercropping using Leucaena leucocephala and fertilizer application on growth and yield of garden eggs (<i>Solanum melongena</i>)

Field trials were conducted in Ghana to assess the effect of applying Leucaena prunings as mulch and N.P.K., 15-15-15 compound fertilizer on the growth and yield of garden eggs (Solanum melongena) during the 1993 minor and 1994 major cropping seasons. The crop was grown with or without Leucaena mulch as well as 0 kg/ha, 180 kg/ha and 360 kg/ha rates of fertilizer. The crop responded very well to the 15-15-15 compound fertilizer used, since plants without fertilizer had significantly reduced height; more days to flowering, fruiting and harvesting and produced yields far below the potential yield levels of the crop. In both seasons, applying the Leucaena mulch increased the mean yield by 21 percent over the no mulch treatments. Economic analysis of the various treatments showed that: producing the crop during the minor season with rainfall was not profitable; producing the crop during the major season was profitable when the half rate of fertilizer, mulched (F1M1 ); full rate fertilizer, mulched (F2 M1 ) and full rate fertilizer no mulch (F2 M0 ) treatments were applied, with the F1M1 ranking first as the most profitable option. This was shown by the comparative net income per hectare of: ¢1,215,000, ¢1,201,020 and ¢819,020 for the (F1M1 ), (F2M1 ) and (F2M0 ) respectively. Producing garden eggs with Leucaena mulch in hedgerow intercropping could reduce fertilizer requirement, at least by half. Hedgerow intercropping with garden eggs is therefore profitable and may become an attractive alternative to small-scale farmers as prices of inorganic fertilizer continue to increase over the years. Journal of Science and Technology (Ghana) Vol. 27 (2) 2007: pp. 62-70

Phosphorus and Potassium Release Pattern from Leucaena Leaves in Three Environments of Haiti

In tropical ecosystems trees have the potential to supply nutrients essential to crops. Leucaena [Leucaena leucocephala (Lam) De Wit] leaf decomposition experiments were established at three sites in Haiti representing diverse soil types to assess the potential of leucaena leaves to supply P and K to crops and to determine their pattern of release. Mesh bags containing 17.4 g of air-dried leucaena leaves were placed in plots receiving 100 kg ha−1 of N as ammonium sulfate and leucaena prunings as mulch with and without 60 kg ha−1 of P and 40 kg ha−1 of K fertilizers for each crop. One bag from each plot was retrieved periodically over a period of 32 weeks for ash free dry matter, P and K determination. In the three locations applications of P–K inorganic fertilizer had no significant effects on leucaena leaf ash free dry matter remaining, P and K concentration nor content of leaves. Cumulative leucaena leaf P content release after 32 weeks of decay for the three sites averaged 4.9 kg ha−1. Cumulative leucaena leaf K content release for the three sites was about 35.4 kg ha−1. The rate of K release was higher in very humid climate than in semi-humid climate. The pattern of leucaena leaf ash free dry matter remaining, residual P and K content followed a double exponential model of decomposition for the three locations. Leucaena leaves applied at the three sites showed potential to supply P and K to crops. Plant material quality, time of decomposition and tree age should be investigated in future studies.

Hedgerow Pruning Management Effects on Maize Yield and Nitrogen Uptake in an Alley Cropping System in Haiti

Hedgerow management is crucial to successful alley cropping. Leucaena [Leucaena leucocephala (Lam.) de Wit] hedgerow management practices were assessed over four seasons for effect on maize (Zea mays L.) yield and N recovery in alley cropping. Maize was planted between leucaena hedgerows spaced 4 m apart on a Lithic Eutropepts. Pruning application and regime factors were arranged in 3 × 3 factorial augmented with a control (stone walls) in randomized complete block design with three replicates. Hedgerows were pruned at 0.50 m height at (a) maize planting and at 30 d after planting (DAP), (b) planting and 40 DAP, or (c) planting, 30 and 60 DAP. Prunings were (a) removed from plots, (b) applied as mulch or (c) incorporated into the soil at planting. A hedgerow + fertilizer treatment in an adjacent trial was included for comparison. Soil application of leucaena prunings increased average maize yield and grain N uptake by 157 and 163%, respectively, compared to when prunings were removed. Addition of inorganic fertilizer further increased maize yield and N recovery. Pruning three times per season gave higher maize yield, N uptake and N recovery than pruning twice, but reduced leucaena biomass and N yield. Pruning twice per season, with the second pruning at 40 rather than at 30 DAP, increased biomass N yield but reduced N recovery over the seasons. Alley cropping with soil application of three prunings per season averaged 31% higher maize yield and 48% higher N uptake than control. N recovery was enhanced by soil application of three prunings per crop and by fertilization.

Alley cropping of maize with calliandra and leucaena in the subhumid highlands of Kenya: Part 2. Soil-fertility changes and maize yield

Although N-rich leaf biomass of multipurpose trees is known to be a good source of N to crops, integrating such trees into crop production systems is a major challenge in the development of viable agroforestry systems. An approach to integrating calliandra (Calliandra calothyrsus Meissner) and leucaena (Leucaena leucocephala (Lam.) de Wit), two promising agroforestry tree species, into maize (Zea mays L.) production system was investigated in the subhumid highlands of central Kenya during four maize-growing seasons from 1994 to 1996. The experiment consisted of maize plots to which tree prunings obtained from hedgerows grown either in situ (alley cropping) or ex situ (biomass transfer from outside) were applied. When alley-cropped with leucaena, maize produced significantly higher yields compared to maize monoculture (both non-fertilized and fertilized) treatments, but when alley-cropped with calliandra, the yield of maize was less than that of the monocropped unfertilized control. Application of ex situ grown calliandra and leucaena prunings with or without fertilizer resulted in higher maize grain yield than in the nonfertilized and fertilized treatments. Yields of calliandra alley- cropped maize were 11% to 51% lower than those of nonalley-cropped treatments receiving calliandra prunings from ex situ grown trees; the decrease was 2% to 17% with leucaena, indicating that calliandra hedges were more competitive than leucaena hedges. The alley-cropped prunings-removed treatments produced the lowest maize yields. The study showed that, in the subhumid tropical highlands of Kenya, inclusion of calliandra hedges on cropland adversely affected maize yields. On the other hand, alley cropping with leucaena was advantageous.

Longterm alley cropping with four hedgerow species on an Alfisol in southwestern Nigeria – effect on crop performance, soil chemical properties and nematode population

A longterm alley cropping trial was undertaken on an eroded Oxic paleustalf in the forest-savanna transition zone of southwestern Nigeria from 1981–1993. Two nitrogen fixing hedgerow species (Gliricidia sepium and Leucaena leucocephala) and two non legume hedgerow species (Alchornea cordifolia and Dactyladenia barteri) were used in the trial compared to a control (with no hedgerow) treatment. Plots were sequentially cropped with maize (main season) followed by cowpea (minor season). With 4 m interhedgerow spacing and pruning at 0.75 m height, the mean annual pruning biomass yields were observed in the following order: Leucaena (7.1 t ha-1 ) > Gliricidia (4.9 t ha-1 ) > Alchornea (3.7 t ha-1) > Dactyladenia (3.0 t ha-1 ). Alley cropping with the four woody species greatly enhanced the total plot (woody species + crop) biomass yield/ha as follows; Leucaena (21.8 t ha-1) > Gliricidia (17.7 t ha-1) > Alchornea (11.7 t ha-1) > Dactyladenia (9.5 t ha-1). Total biomass yield of crops in control plot was 5.3 t ha-1. Higher biomass yields with alley cropping also increased nutrient yield and cycling. Gliricidia and Leucaena showed higher nutrient yields than Alchornea and Dactyladenia. Alley cropping with Gliricidia and Leucaena could sustain maize yield at moderate level (>2 t ha-1), which would require a N-rate of 45 kg N ha-1 with sole cropping. Application of N in Gliricidia and Leucaena alley cropping still improved maize yield. Higher nitrogen rates are required for alley cropping with Alchornea and Dactyladenia hedgerows. A low rate of phosphorus application is needed for sustaining crop yields with all treatments. Occasional tillage is recommended to increase maize yield. Alley cropping and tillage showed little effect on cowpea seed yield. Surface soil properties declined with time with continuous cultivation. Alley cropping with woody species maintained higher soil organic carbon, phosphorus and potassium levels. Plots alley cropped with Gliricidia and Leucaena showed lower pH and extractable calcium level. Leucaena alley cropped plot also showed lower magnesium level. The decline in soil pH and extractable cations may be due to increased cation leaching with application of high rates of Gliricidia and Leucaena prunings. Alley cropping with the four woody species showed no effect on population of parasitic nematodes.

Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands I. Decomposition and nutrient release

A litter bag technique was used to study the decomposition and release of N, P, K, Ca, and Mg from Leucaena leucocephala and L. pallida prunings and cattle manure in a hedgerow intercropping trial conducted in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping or alley farming) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. Manure was the most resistant to decomposition, losing only 15% of its dry matter (DM) in 15 weeks, compared to 41–57% lost by leucaena prunings. Large quantities of K (up to 104 kg ha–1) were mineralized from prunings and manure, but Ca and Mg were mostly immobilized. More N and P were released from prunings than from manure, which resulted in net immobilization of these nutrients in the initial stages of decomposition and net mineralization in later stages. Between the leucaenas more N was mineralized and less Ca and Mg were immobilized when L. leucocephala prunings were applied than when L. pallida prunings were applied. Fertilizer N increased DM decomposition and N mineralization. Mineralization of the nutrients was constrained by lignin and polyphenol contents. It is concluded that leucaena mulch and cattle manure may be significant sources of N and K for crop growth, but external sources of P, Ca and Mg may be required, particularly in acid soils which have low contents of these nutrients. However, this fertility effect has to be evaluated against the competition effect of trees to predict crop response.

Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands III. Nutrient balances

Balances between nutrients applied or mineralized and nutrients removed in maize grain and stover were calculated in a hedgerow intercropping experiment in which Leucaena leucocephala and L. pallida prunings and cattle manure were applied. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. In control treatments, nutrient depletion per season was in the order of 7–19 kg N ha–1, 4–12 kg P ha–1, 10–26 kg K ha–1, 0–2 kg Ca ha–1 and 3–6 kg Mg ha–1. N fertilizer reversed the depletion of N, but it accelerated the depletion of the other nutrients. Manure and at least two applications of leucaena prunings resulted in net positive balances of N, K, and Ca between amounts applied or mineralized and amounts removed by maize. The amounts of P and Mg applied with, or mineralized from, prunings or manure were insufficient to offset the negative balances of these nutrients.

Alley cropping of sorghum with Leucaena during the post-rainy season on Vertisols in semi-arid India

A field experiment was conducted for two years (1989– 1991) on a Vertisol in Bijapur, India in a split-plot design, replicated four times, to evaluate the potential of alley cropping post-rainy season sorghum between Leucaena hedgerows. Leucaena produced on average 2.74 t per ha of prunings and 1.57 t per ha of wood annually. Alley cropping decreased sorghum yields by 28 to 45% when all Leucaena prunings were removed from the system and by 21 to 24%, when on average 1.92 t per ha prunings were applied to the soil annually. The reduction of sorghum yield increased as higher rates of N were applied to sorghum. Although alley cropping increased organic carbon by 21% and available N by 19% at the time of crop sowing, it did not result in increased crop yields because of competition for water between hedgerows and crops. Calculation of land equivalent ratios based on total Leucaena biomass indicated that alley cropping was more productive than sole cropping of sorghum only in one year, and that, too, when no N was applied to sorghum. Therefore, alley cropping of Vertisols with post-rainy season sorghum is not likely to have any advantage in the short term.

Agronomic and economic evaluation of methods of establishing alley cropping under a maize/groundnut intercrop system

Agronomic and economic benefits of maize intercropped with groundnut in alleys formed by Leucaena leucocephala were assessed at Matomb, Cameroon, from 1990 to 1992: (a) without fertilizers and (b) with the application of 200 or 400 kg ha −1 of N-P 2O 5-K 2O (20-10-10). In treeless (control) plots, maize grain yields decreased from 1.2 t ha −1 in 1990 to 0.8 t ha −1 in 1992, while groundnut yields declined from 1.1 to 0.5 t ha −1 during the same period. With the application of Leucaena prunings alone, groundnut yield was maintained around 1 t ha −1 for 3 years while maize yields stabilized at 2.5 t ha −1 in the second and the third year; the yields of both crops were greater over the 3 years than in the control. Leucaena prunings applied in combination with 200 and 400 kg ha −1 of N 2-P 2O 5-K 2O increased maize yield by 1.7 and 2.0 t ha −1, respectively, but groundnut yield decreased by 13 and 24% over the 3 years. The dominance analysis showed that alley cropping without fertilizer was the only non-dominated alternative, with a marginal rate of return of 447%. It was the best system at this early stage (3 years) of implementing the technology.

Effect of various mulches on soil microarthropods under a maize crop

Soil microarthropod populations in maize plots mulched with the prunings of three woody agroforestry plant residues (Acioa barteri, Gliricidia sepium and Leucaena leucocephala) and two crop residues [maize (Zea mays) stover (leaves and stems) and rice (Oryza sativa) straw] were monitored throughout the 1991 growing season and compared with those in fallow, bare fallow and unmulched control plots with three rates of nitrogen application. The mean densities of detritivore and phytophage microarthropods in the experimental plots decreased in the following order: rice straw > Gliricidia prunings > Leucaena prunings > maize stover > Acioa prunings > control 2 (90 kg N ha-1 year-1) > fallow > control 3 (135 N) > control 1 (45N) > bare fallow. Mulching also affected the population dynamics of predatory microarthropods and omnivorous ants. The chemical composition of plant residues probably influenced the densities of detritivore and phytophage microarthropods, which in addition were also greatly influenced by microclimatic conditons imposed by vegetation cover. Extremely low densities of microarthropods were recorded in the bare fallow plots probably as a result of the combined effects of absence of plant residues and vegetation cover. The potential of mulching as a component of farming practice for increasing the density of microarthropods and for influencing their species composition and population dynamics in agroecosystems is discussed.

Mulching effect of plant residues with chemically contrasting compositions on maize growth and nutrients accumulation

Effects of application of prunings of three woody species (Acioa barteri, Gliricidia sepium and Leucaena leucocephala), maize (Zea mays L.) stover and rice (Oryza sativa L.) straw as mulch on maize were studied on an Alfisol in southern Nigeria in 1990 and 1991. Maize dry matter and grain yield were higher with applications of plant residues and N fertilizer in both years. Addition of Leucaena prunings gave the highest maize grain yield in both years. Compared to the 1990 results, Acioa showed the least grain yield decline among the mulch treatments in 1991. Nutrient uptake was enhanced by applications of plant residues. Leucaena prunings had the highest effect in both years and increased the mean N, P, and Mg uptake by 96%, 84%, and 50%, respectively, over the control. Addition of Acioa prunings increased K and Ca uptake by 59% and 92%, respectively, over the control. ‘High quality’ (low C/N ratio and lignin level) plant residues enhance crop performance through direct nutritional contributions, whereas ‘low quality’ (high C/N ratio and lignin level) plant residues do so through mulching effects on the microclimate. ‘Intermediate quality’ plant residues have no clear effects on crop performance.

Biological effects of plant residues with contrasting chemical compositions under humid tropical conditions: Effects on soil fauna

Effects of application of five types of plant residues [ Acioa barteri, Gliricidia sepium and Leucaena leucocephala prunings, maize ( Zea mays) stover and rice ( Oryza sativa) straw] as mulch on soil fauna were examined under field conditions in the humid tropics in 1990 and 1991. Earthworm mean population over 2 years was higher under any type of plant residues by 41% compared to control. Leucaena prunings supported the highest earthworm population. Mulched plots also showed 177% higher mean termite population over 2 years than control. Highest termite population was observed in plots mulched with Acioa prunings followed by maize stover > rice straw > Leucaena prunings > Gliricidia prunings. The mean ant populations were 36% higher with Leucaena and Gliricidia prunings, and were not affected by Acioa prunings, maize stover and rice straw as compared to control. Millipede populations were not significantly affected by mulching. Earthworm populations were negatively correlated with the ratio of lignin : N of plant residues. Ant populations were significantly related to the N content of plant residues ( R 2 = 0.87 and 0.84 for 1990 and 1991 respectively). The results imply that chemical plant composition, particularly N and lignin contents, play a critical role in faunal abundance in the soil through their effect on palatability and decomposibility. Indirect microclimatic and mulching effects may also be important.

Nitrogen cycling in leucaena (Leucaena leucocephala) alley cropping in semi-arid tropics

The success of alley cropping depends to a large extent on the efficiency of transfer of nitrogen (N) from the legume hedgerow plants to the non-legume crop. Here the idea is examined that leucaena prunings (residues) can supply enough N to maize plants to significantly reduce the degree of N deficiency. Two experiments on decomposition of leucaena leaf, stem, and petiole and mineralization of N from leucaena residues were conducted in field microplots which received application of either15N-labelled leucaena materials or ammonium sulphate fertilizer. The microplots were installed in alleys formed by leucaena hedgerows spaced 4.5 metres apart and cropped with maize. The decomposition of leucaena leaves, stems and petioles was estimated by several methods. The decomposition ranged from 50–58% with leaves, 25–67% with stems and 38–51% with petioles 20 days after addition. More than 55% of the N was released in 52 days during decomposition of leucaena residues. By 20 days after application of15N-labelled leucaena 3.3–9.4% of the added15N was found in the maize plants, 32.7–49.0% was in the leucaena residues, 36.0–48.0% in the soil and 0.3–21.9% lost (deficit). By 52 days 4.8% of the15N applied in leucaena prunings was taken up by maize, 45.1% was detected in the residues, 24.9% in the soil and 25.2% lost. However, when N fertilizer was applied, 50.2% of the fertilizer N was recovered by maize, 35.5% was retained in the soil and 14.3% apparently lost. There was a marked increase in maize plant dry matter and N uptake in the microplots with addition of leucaena prunings compared with those in the microplots without leucaena added. Most of the15N remaining in the soil profile, derived from leucaena residues, was detected in the top 25 cm soil with less than 2% found below 25 cm. ei]H Lambers

Nitrogen cycling in leucaena (Leucaena leucocephala) alley cropping in semi-arid tropics

In an alley cropping system, prunings from the hedgerow legume are expected to supply nitrogen (N) to the associated cereal. However, this may not be sufficient to achieve maximum crop yield. Three field experiments with alley-cropped maize were conducted in a semi-arid environment in northern Australia to determine: (1) the effect of N fertilizer on maize growth in the presence of fresh leucaena prunings; (2) the effect of incorporation of leucaena and maize residues on maize yield and the fate of plant residue 15 N in the alley cropping system; and (3) the 15 N recovery by maize from 15 N-labelled leucaena, maize residues and ammonium sulphate fertilizer []

Biological effects of plant residues with contrasting chemical compositions under humid tropical conditions—Decomposition and nutrient release

Decomposition and nutrient release patterns of prunings of three woody agroforestry plant species ( Acioa barteri, Gliricidia sepium and Leucaena leucocephala), maize ( Zea mays) stover and rice ( Oryza sativa) straw, were investigated under field conditions in the humid tropics, using litterbags of three mesh sizes (0.5, 2 and 7 mm) which allowed differential access of soil fauna. The decomposition rate constants ranged from 0.01 to 0.26 week −1, decreasing in the following order; Gliricidia prunings > Leucaena prunings > rice straw > maize stover > Acioa prunings. Negative correlations were observed between decomposition rate constants and C:N ratio ( P < 0.004), percent lignin ( P < 0.014) and polyphenol content ( P < 0.053) of plant residues. A positive correlation was observed between decomposition rate constant and mesh-size of litterbag ( P < 0.057). These results indicate that both the chemical composition of plant residues and nature of the decomposer played an important role in plant residue decomposition. Nutrient release differed with quality of plant residues and litterbag mesh-size. Total N, P, Ca and Mg contents of plant residues decreased with time for Gliricidia and Leucaena prunings, maize stover, and rice straw, and increased with time for Acioa prunings. There was some indication of N immobilization in maize stover and rice straw; P immobilization in Leucaena prunings and rice straw; and Ca immobilization in maize stover, rice straw and Gliricidia and Leucaena prunings. Acioa prunings immobilized N, P, Ca and Mg. All plant residues released K rapidly. Nutrient release increased with increasing mesh-size of litterbags, suggesting that soil faunal activities enhanced nutrient mobilization.

Effect of alley cropping with Leucaena leucocephala and fertilizer application on yield of vegetable crops

Field experiments were conducted to investigate the effect of alley cropping vegetable crops with Leucaena leucocephala (Lam.) de Wit for two seasons on a sandy loam Oxic paleustalf in southwestern Nigeria. Four vegetable crops (Amaranthus cruentus L.; Celosia argentea L.; Okra, Hibiscus esculentus L.; and tomato, Lycopersicon esculentum Mill.) were grown in control plots and in 4-m wide alleys between established Leucaena hedgerows without and with fertilizer (30 N-13 P-24 K kg ha−1). Leucaena prunings yielded large dry biomass and nutrients during both seasons. Yield of four vegetable crops responded more to fertilizer in control than in alley cropped treatments. Better yield of vegetables in alley cropped plots was in part due to following effect of the Leucaena hedgerows. Fertilizer application increased mean yields of Amaranthus, Celosia, okra and tomato by 325, 164, 47 and 94% in control plots and by 36, 26, 4 and 20% in alley cropped plots, respectively. For both seasons, yields were not significantly different between alley cropped with and without fertilizer and the control with fertilizer treatments. Yield was least in control without fertilizer. Alley cropping with Leucaena can reduce fertilizer requirement for vegetable production. Cost and return analysis using 1988 prices indicated that alley cropping with vegetable crops can be profitable.

Nitrogen fertilizer in leucaena alley cropping. I. Maize response to nitrogen fertilizer and fate of fertilizer-15N

Field microplot experiments were conducted in the semi-arid tropics of northern Australia to evaluate the response of maize (Zea mays L.) growth to addition of N fertilizer and plant residues and to examine the fate of fertilizer15N in a leucaena (Leucaena leucocephala) alley cropping system, in which supplemental irrigation was used. Leucaena prunings, maize residues and N fertilizer were applied to alley-cropped maize grown in microplots which were installed in the alleys formed by leucaena hedgerows spaced 4.5 metres apart. The15N-labelled fertilizer was used to examine the fate of fertilizer N applied in the presence of mulched leucaena prunings and maize residues.