Alley Cropping System Research Articles

Carbon and nitrogen in a temperate agroforestry system: Using stable isotopes as a tool to understand soil dynamics

Natural exchanges of carbon (C) between the atmosphere, the oceans, and terrestrial ecosystems are currently being modified through human activities as a result of fossil fuel burning and the conversion of tropical forests to agricultural land. These activities have led to a steady increase of atmospheric carbon dioxide (CO 2) over the last two Centuries. The goal of this study was to determine the potential of temperate agroforestry systems to sequester C in soil. Therefore, changes in the soil organic C (SOC) and nitrogen (N) pools were quantified and the δ 13C and δ 15N stable isotope technique was applied to assess soil C and N dynamics in a 13-year old hybrid poplar alley cropping system in Southern Canada. Results from this study showed that after 13 years of alley cropping the SOC and N pools did not differ significantly ( p = 0.01) with distance from the tree row, although a trend of a larger SOC and N pool near the tree row could be observed. Soil organic C after 13 years of alley cropping, was 19 mg C g −1 compared to 11 mg C g −1 upon initiation of agroforestry. Soil organic C and N were not evenly distributed throughout the plow layer. The largest C and N pool occurred in the top 20 cm, which is due to the accumulation of organic material in the upper horizons as a result of no-till cultivation. The entire soil, to a 40 cm depth, showed a δ 13C shift to that of C 3 residue. This shift reflects the greater input of residues from C 3 plants such as that derived from beans, wheat, and hybrid poplar leaf litterfall. The proportion of C derived from a C 3 source ranged from 64 to 69% to a 40 cm depth. The soil δ 15N signature of this study is similar to that of mineral soil, and reflect values characteristic of N mineralization processes. However, the entire soil shows a positive shift in δ 15N as a result of historical additions of manure and current use of mineral fertilizers, and ongoing processes of denitrification and nitrate leaching, which leads to an enrichment of the soil.

Interspecific competition in a pecan–cotton alleycropping system in the southern United States: Production physiology

A study was conducted on a Red Bay sandy loam soil (Rhodic Paleudult) in Jay, Florida, USA, to investigate how interspecific interactions between pecan ( Carya illinoensis K. Koch) and cotton ( Gossypium hirsutum L.) would affect cotton leaf morphology and gas exchange and thereby biomass and lint yield. We quantified specific leaf area (SLA), specific leaf nitrogen (SLN), net photosynthesis (A), transpiration, stomatal conductance, and net canopy photosynthetic index (CNPI) from cotton with and without aboveground and belowground interactions. To separate roots of cotton and pecan, polyethylene-lined trenches were installed (barrier treatment) parallel to tree rows in half the number of plots. Results showed that SLA for barrier and nonbarrier plants was 61% and 47% higher, respectively, compared with the monoculture cotton. Monoculture plants exhibited higher CNPI (70.7 μmol·m–2·s–1) compared with the barrier (52.7 μmol·m–2·s–1) and nonbarrier plants (18.3 μmol·m–2·s–1). SLN was similar for both the barrier and nonbarrier plants; however, it was lower than the monoculture. A positive curvilinear relationship between A and SLN was observed, with peak A (28 μmol·m–2·s–1) observed between 2.2 and 2.4 mg N·m–2. Significant curvilinear relationships between CNPI and aboveground biomass and lint yield were also observed for all treatments. These findings indicate that competitive interactions in alleycropping regulate leaf level traits such as SLA and SLN by altering water and light availability, which in turn exert a profound influence on aboveground biomass and lint yield for cotton plants.

Morphological plasticity of cotton roots in response to interspecific competition with pecan in an alleycropping system in the southern United States

A study was conducted in northwest Florida, USA, to investigate root development and morphology of cotton (Gossypium hirsutum L.) under pecan (Carya illinoensis K. Koch) trees in an alleycropping experiment. Root:shoot ratio, root biomass, total root length and root length density were examined under three treatments: (1) barrier (separating belowground interspecific competition by trenching to a depth of 120 cm and installing polyethylene barrier), (2) non-barrier (root systems were free to interact), and (3) monoculture of cotton (without above and belowground interspecific competition with trees). Results indicated that plants in the barrier and non-barrier treatments had lower root:shoot ratios compared to the monoculture treatment. Belowground competition for resources between pecan and cotton in the non-barrier treatment resulted in 25 and 33% reduction of total root length (359 cm) when compared to that of the barrier (477 cm) and monoculture (539 cm) treatments, respectively. The non-barrier plants also exhibited the lowest root length density. Specific root length was highest for the monoculture (179 cm g−1) and lowest for the non-barrier treatment (146 cm g−1) with the barrier treatment being intermediate (165 cm g−1). Interspecific competition with pecan significantly altered root development and morphology of cotton plants. Research in agroforestry should take into account the developmental differences in root systems of the associated crop species so that better models incorporating nutrient and water uptake can be developed.

Soil carbon dynamics and residue stabilization in a Costa Rican and southern Canadian alley cropping system

Agroforestry systems can play a major role in the sequestration of carbon (C) because of their higher input of organic material to the soil compared to sole crop agroecosystems. This study quantified C input in a 19-year old tropical alley cropping system with E. poeppigiana (Walp.) O.F Cook in Costa Rica and in a 13-year old hybrid poplar (Populus deltoides × nigra DN-177) alley cropping system in southern Canada. Changes in the level of the soil organic carbon (SOC) pool, residue decomposition rate, residue stabilization efficiency, and the annual rate of accumulation of SOC were also quantified in both systems. Carbon input from tree prunings in Costa Rica was 401 g C m−2 y−1 compared to 117 g C m−2 y−1 from litterfall at the Canadian site. In southern Canada, crop residue input from maize (Zea mays L.) was 212 g C m−2 y−1, 83 g C m−2 y−1 from soybeans (Glycine max L.) and 125 g C m−2 y−1 for wheat (Triticum aestivum L.), and was not significantly different (p < 0.05) from the sole crop. The average yearly C input from crop residues in Costa Rica was significantly greater (p < 0.05) in the alley crop for maize (134 g C m−2 y−1) and Phaseolus vulgaris L. bean crops (35 g C m−2 y−1) compared to the sole crop. The SOC pool was significantly greater (p < 0.05) in the Costa Rican alley crop (9536 g m−2) compared to its respective sole crop (6143 g m−2) to a 20 cm depth, but no such difference was found for the southern Canadian system. Residue stabilization, defined as the efficiency of the stabilization of added residue (crop residues, tree prunings, litterfall) that is added to the soil C pool, is more efficient in southern Canada (31%) compared to the alley cropping system in Costa Rica (40%). This coincides with a lower organic matter decomposition rate (0.03 y−1) to a 20 cm depth in Canada compared to the Costa Rican system (0.06 y−1). However, the average annual accumulation rate of SOC is greater in Costa Rica (179 g m−2 y−1) and is likely related to the greater input of organic material derived from tree prunings, compared to that in southern Canada (30 g m−2 y−1) to a 20 cm depth.

Effect of mycorrhiza and pruning regimes on seasonality of hedgerow tree mulch contribution to alley-cropped cassava in Ibadan, Nigeria

Field experiments were carried out on an alley-cropping farm in Ajibode village, near Ibadan where cassava alley-cropped with three hedgerow trees (Leucaenaleucocephala, Gliricidia sepium and Senna (Syn Cassia) siamea), and sole planted cassava (all in three replicates) were arranged with arbuscular mycorrhizal fungi (AMF) inoculation (with Glomus deserticolum) in a completely randomized block design. Each plot was split after the first year into two and hedgerows within subjected to 2 and 3-month pruning regimes. Wet and dry season mulch contribution by pruning to alley-cropped cassava, as well as cassava yield characteristics in both alley-cropped and sole plots as affected by AMF inoculation and pruning regimes were monitored over two consecutive planting periods. During the first pruning year, AMF inoculation promoted dry season pruning production which was masked in Leucaena at 3 months by biomass diversion into flowering and in Gliricidia with both flowering and mite infestation. No definite patterns were observed in the second pruning year due to development of indigenous AMF symbiosis in all plots. Total yield of cassava increased with inoculation in all plots but dry season leaf area values and tuber yield indices were relatively higher in cassava alley-cropped with Senna and sole cassava than in others. The low total yield of sole cassava makes cassava alley cropped with Senna (inoculated or uninoculated) the best option for maintaining steady tuber yield with time in a continuing alley-cropping system. Key words: Biomass diversion, cassava tuber yield index, mycorrhizal contribution.

(60) Establishment and Growth of Ginger Lilies Under a Sustainable Agroforestry Production System with Moringa in the U.S. Virgin Islands

Specialty cut flowers may be suited to sustainable production system in the tropics and an agroforestry approach was developed to add a commercial value to unused forest areas. Ginger lily (Alpinia purpurata), a specialty tropical cut flower, was planted under a sustainable alley cropping system with moringa (Moringa oleifera), to evaluate the biophysical interactions between system components. Moringa trees were planted in rows 5 m apart and were 5 years old at the time ginger lilies were planted on 1 June 2005. Two rows of ginger lilies spaced 0.6 m in row and 1.7 m between rows were planted on a 1-foot-high bed between moringa rows when trees were about 6 m tall. Alley plot length was 10 m. After a month, plant establishment was 96%. In July, the moringa trees were pruned down to 1.5 m and the biomass (foliage) was used as green manure. Ginger lilies were also mulched with straw. Plots were gradually shaded as moringa shoots developed reducing the photosynthetic photon flux to 40% of direct sun light in September and to 15% four months later. Six months after planting, height and number of shoots in shaded ginger lilies were 58% and 30% of plants in full sun, respectively. Ginger lilies began to flower 5 months after planting in the sunny plots, but no flowers were produced after 7 months in the shady plots. Since soil and tissue nitrate-N was the same between treatments, moringa biomass appears to be insufficient to increase the nutrient status of the crop. In addition, the low light intensity in the alley appears to be suboptimal for growth and production of ginger lilies.

Phosphorus loss from organic versus inorganic fertilizers used in alleycropping on a Florida Ultisol

The status of residual phosphorus (P) and nitrogen (N) in agricultural soils is an environmental concern due to the possibility of the nutrients reaching adjacent water bodies through leaching or runoff. This concern is of particular importance in sandy and other coarse-textured, highly permeable soils. A 3-year study examined a pecan ( Carya illinoensis K. Koch)–cotton ( Gossypium hirsutum L.) alleycropping system situated on an Ultisol in northwest Florida, USA, to determine the effects of tree–root competition and fertilizer application (poultry litter versus inorganic) on soil nutrient status with time. Overall, competition for P between tree and crop roots appeared to be minimal in these soils. However, build-up of P occurred in soil over time. After 2 years of fertilizer application in the alleycropping system, the average concentration of Mehlich 1-P in the surface soil (0–5 cm) increased from 74 to 106 mg kg −1 , and water soluble P increased from 5.9 to 7.2 mg kg −1 . In addition, accumulation of P in near-surface soils was slightly higher in manure-treated soils after the first year of treatment. A clay layer in the Ultisol at approximately 25 cm largely prevented further downward movement of P. Overall, in terms of potential environmental risks from P accumulation and loss via runoff or leaching in these soils, the organic fertilizer appears to pose a greater long-term risk than the inorganic fertilizer if application is based on plant N requirement (a common practice) rather than P requirement.

Soil Organic Carbon and Nitrogen Fractions in Temperate Alley Cropping Systems

Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic carbon (C) and nitrogen (N) fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley cropped sites, a 19‐yr‐old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (pecan site) and an 11‐yr‐old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (maple site). Particulate organic matter (POM) C constituted 15–65% and 14–41% of total organic C (TOC) at the pecan and maple sites respectively, whereas POM N comprised 3 to 24% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0–10 cm) at the pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley for subsurface soils at the maple site. No differences in microbial biomass C and N between positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.

Incidence and Severity of Bean Rust (Uromyces appendiculatus) in Alleys between Leucaena Hedgerows in Kenya

The effects of inter-row spacing of Leucaena leucocephala (Lam.) de Wit in an alley cropping system on the incidence and severity of rust (Uromyces appendiculatus (Pers.) Unger) on intercropped beans (Phaseolus vulgaris L.) and their yield were examined over 2 years (1993 and 1994) at Chepkoilel Campus in Kenya. Each experiment consisted of three randomized blocks with treatments of three alley widths (2 m, 4 m and 8 m) and a treeless control with two intra-row spacings of Leucaena (0.5 m and 1.0 m). Hedgerows were coppiced at 1.0 m height and pruned subsequently at 2–3 months intervals. No fertilizer was applied but Leucaena loppings were incorporated as green leaf manure. Rust on beans was assessed at three growth stages in each season, using the Centro International de Agricultura Tropical (CIAT) scales. Microclimate was monitored in treatments, in 1994. Bean growth and yield were also measured. Rust increased with increasing alley width and was less severe in bean rows adjacent to hedgerows. Bean yield was highest in the treeless control plots and declined with decreasing alley width. Beans in 2 m alleys had significantly lower (p < 0.05) yields than 8 m alleys and treeless control plots. Bean growth was greatly modified in 2 m alleys and close to hedgerows. Light availability and diurnal temperature increased with alley width but relative humidity and leaf wetness duration decreased. Proximity to hedgerows also had marked effect on microclimate. The changes in yield, rust incidence and severity were examined in relation to microclimate, inoculum survival and dispersal.

Comparative morphophysiological and yield characteristics of musa genomes in Nigeria

Thirty-six (36) Musa genotypes comprising tetraploid hybrids and triploid land races belonging to AAA, AAB, and ABB Musa genomes were evaluated in three agro-ecologies following a South-North rainfall and Vegetation gradients in Nigeria. Plants were grown as sole crops at Onne (High rainforest zone), Ibadan (forest-savannah transition zone) and Abuja (Southern guinea savannah zone) plus an additional experiment grown in alley cropping system at Onne. Phenological and yield traits were measured for two crop cycles. The results revealed that crop cycle did not yield traits were measure for two crop cycles. The results revealed that crop cycle did not significantly influenced height of the tallest sucker at harvest of the paint crop, black sigatoka disease responses and the fruit weight. All phonological and yield traits were significantly (P Bio-Research Vol. 3(1) 2005: 45-55

Influence of cropping intensity on the production and properties of earthworm casts in a leucaena alley cropping system

The effect of cropping intensity on surface cast production by earthworms was studied more than 4 years in an alley cropping system. The plots were cultivated to maize–cassava intercrop every year (100% cropping intensity), after 2 years of fallow (33% cropping intensity) and after 3 years of fallow (25% cropping intensity). Cast production was assessed by the continuous sampling technique proposed by Hauser and Asawalam (Z Pflanzenernahr Bodenkd 161:23–30, 1998). Results showed that cropping intensity enhanced cast production in the first year, did not affect it in the second and third years and decreased cast production in the fourth year. Amount of casts deposited within the alleys was highest under the hedgerow and decreased towards the middle of the alley. The concentrations of organic matter and plant nutrients were significantly higher in worm casts than in soil, irrespective of the cropping intensity and position of sample collection within the interrow space. Continuous cropping up to 6 years significantly reduced the concentrations of organic carbon, total nitrogen, available phosphorus, and exchangeable calcium, potassium and magnesium in the top 0–5 cm of the soil, irrespective of the distance from the hedgerow. Regardless of the intensity of cropping, there is a strong linear association between the quantity of casts and the amount of organic carbon, and other nutrients in casts.

The use of Arbuscular Mycorrhiza (AM) as a source of yield increase in sustainable alley cropping system

The use of Arbuscular Mycorrhiza (AM) as an aid for yield increase in sustainable alley cropping system was investigated in this study at different sites within the same region in Nigeria. The results show that alley cropping improved cassava yield more than fertilizer application. It was found that either Arbuscular Mycorrhiza (AM) or inorganic fertilizer can be substituted for each other when cassava is alley-cropped with Cajanus cajan (L. Millsp). In cassava (Manihot esculenta, Crantz) and cowpea (Cajanus cajan L. Millsp), Arbuscular Mycorrhiza (AM) inoculation significantly increased the crop yield more than the uninoculated treatment. Cassava mulched with the leguminous shrub had very low yield (T3) compared to the one with AM treatment (T2). But when inorganic fertilizer was added (T1), the yield was better than T3. However, T2 yielded more than other treatments, without application of inorganic fertilizer, Arbuscular Mycorrhiza (AM) made the locked up nutrients in the soil available to the plants and enhanced N-fixation of the plants.

Influence of mycorrhizal inoculation on alley cropped farms in a humid tropical environment

The use of Arbuscular mycorrhizal (AM) fungi under farmers' conditions was tried at Ajibode Village, a humid tropical environment on maize/cassava intercropped farms in an alley cropping system. Four species of AM fungi ( Glomus clarum, Glomus mosseae Glomus etunicatum and Acaulospora dilatata ) were used in paired treatment experimental design. Cassava and maize yields on the inoculated plots were higher than the control. It was also found that G. etunicatum was more efficient for cassava while G. mosesae was more efficient for maize. The study concluded that AM fungi inoculation can be easily adopted by farmers in the humid tropics as a low external input sustainable agricultural technology. Key words: Abuscular Mycorrhiza; Fungi; Glomus clarum; Glomus mosseae; Glomus etunicatum; Acaulospora dilatata Moor Journal of Agricultural Research Vol.4(2) 2003: 246-250

Soil carbon and nitrogen dynamics using stable isotopes in 19- and 10-year-old tropical agroforestry systems

Conversion of forests to agricultural land in the American tropics, through traditional agricultural practices such as shifting cultivation, has not been able to maintain stocks of soil organic carbon (SOC), and increasing population pressure has led to shortened fallow periods, causing further losses of soil fertility. However, land management practices such as agroforestry can provide a sustainable alternative to single cropping because of its ability to maintain or increase the SOC pool. This study quantified SOC and nitrogen (N) pools, gross SOC turnover, residue stabilization efficiency (RSE AC) in the alley crop, soil δ 13C partitioning, C 3-C abundance and δ 15N dynamics in 19- and 10-year Gliricidia sepium and Erythrina poeppigiana alley cropping system. Each system was studied at two fertilizer levels (tree prunings only [−N or −A], and tree prunings plus chicken manure [+N], or Arachis pintoi as a groundcover [+A]), and was compared to a sole crop system. The SOC and N pools were significantly higher ( p < 0.05) in the 19-year-old alley crop compared to the sole crop, but not significantly different ( p < 0.05) in the 10-year-old system. Soil C and N (%) showed a similar trend as that of the SOC and N pools in both 19- and 10-year-old systems. Gross SOC turnover, to a 20 cm depth, ranged from 12 to 21 years in the 19-year-old alley crop compared to 50 years in the sole crop, and from 20 to 32 years in the 10-year-old alley crop compared to 106 years in the sole crop. The RSE AC ranged from 10% to 58% in the 19-year-old system, and from 3% to 43% in the 10-year-old system. The δ 13C signature of the soil shifted significantly ( p < 0.05) towards that of C 3 vegetation in the alley crop due to the greater input of organic residues from tree prunings compared to the sole crop. The proportion of input from tree prunings only in the 19-year-old alley crop ranged from 14% to 20%, and from 9% to 11% in the 10-year-old system to a soil depth of 20 cm. The δ 15N signature of the soil showed two patterns: that of the 19-year-old system being enriched in δ 15N, and that of the 10-year-old system being depleted in δ 15N compared to the sole crop. The addition of manure in the 19-year-old system has enriched the soil δ 15N and in the 10-year-old system the soil was depleted due to the N 2-fixing groundcover A. pintoi.

Long-term effects of fallow systems and lengths on crop production and soil fertility maintenance in West Africa

In the development of short fallow systems as alternatives to shifting cultivation in West Africa, a long-term trial was established at the International Institute of Tropical Agriculture (IITA) on an Alfisol in the forest-savanna transitional zone of southwestern Nigeria, comparing three fallow systems; natural regrowth fallow, cover crop fallow and alley cropping on soil productivity and crop yield sustainability. The natural fallow system consisted of natural regrowth of mainly Chromolaena odorata shrub as fallow vegetation. The cover crop fallow system consisted of Pueraria phaseoloides, a herbaceous legume as fallow vegetation. The alley cropping system consisted of woody hedgerows of Leucaena leucocephala as fallow vegetation. The fallow lengths were 0 (continuous cropping), 1, 2 and 3 years after 1 year of maize/cassava intercropping. Biomass produced from natural fallow and cover crop fallow was burnt during the land preparation. Fertilizer was not applied throughout the study. Without fertilizer application, maize yield declined from above 3.0 t ha−1 to below 0.5 t ha−1 during 12 years of cultivation (1989–2000) on a land cleared from a 23-year old secondary forest. Temporal change in cassava tuber yield was erratic. Mean maize grain yields from 1993–2000 except for 1999 were higher in cover crop fallow system (1.89 t ha−1) than in natural fallow system (1.73 t ha−1), while natural fallow system outperformed alley cropping system (1.46 t ha−1). During the above 7 years, mean cassava tuber yield in cover crop system (7.7 t ha−1) did not differ from natural fallow system (8.2 t ha−1), and both systems showed higher cassava tuber than the alley cropping system (5.7 t ha−1). The positive effect of fallowing on crop yields was observed for both crops in the three systems, however, insignificant effects were seen when fallow length exceeded 1 year for cover crop and alley cropping, and 2 years for natural fallow. Soil pH, organic carbon, available P and exchangeable Ca, Mg and K decreased considerably after 12 years of cultivation, even in a 3-year fallow subplot. After 12 years, soil organic carbon (SOC) within 0–5 cm depth in alley cropping (13.9 g kg−1) and natural fallow (13.7 g kg−1) was higher than in cover crop fallow (11.6 g kg−1). Whereas significant increase in SOC with either natural fallow or alley cropping was observed only after 2 or 3 years of fallow, the SOC in the 1-year fallow alley cropping subplot was higher than that in continuous cropping natural fallow subplot. It can be concluded from our study that in transforming shifting cultivation to a permanent cropping, fallow with natural vegetation (natural fallow), herbaceous legumes (cover crop fallow) and woody legumes (alley cropping) can contribute to the maintenance of crop production and soil fertility, however, length of fallow period does not need to exceed 2 years. When the fallow length is reduced to 1 year, a better alternative to natural regrowth fallow would be the cover crop for higher maize yield and alley cropping for higher soil organic matter. For fallow length of 2 years, West African farmers would be better off with the natural fallow system.

Decomposition of Erythrina poeppigiana leaves in 3-, 9-, and 18-year-old alleycropping systems in Costa Rica

Timing the application of organic residues and therefore the release of nutrients during decomposition may be critical to the growing crop in tropical alleycropping agroforestry systems. Field experiments were carried out in Turrialba, Costa Rica, to determine differences in Erythrina poeppigiana (Walp.) O.F. Cook leaf decomposition in 3, 9 and 18-year alleycropped agroforestry systems. Treatments consisted of mulch-only, and mulch plus Arachis pintoi Krapov. and W. Gregory var. CIAT 18347 in 3 and 9-year old alleycrops under no-till cultivation. The 18-year old site consisted of treatments with mulch-only and mulch plus chicken manure under disk plow cultivation. Litterbags, filled with E. poeppigiana leaves from 3, 9 and 18-year old trees, were placed on the soil surface and collected over a period of 84 days. Results showed no significant differences in the amount of plant residues remaining after 84 days in the 3-, 9-, and 18-year-old systems, or between the manure and mulch-only treatments. Comparing mulch-only treatments, leaves in the 18-year old system decomposed most rapidly which may be due to disk-plow cultivation practices where litterbags were in direct contact with the soil as opposed to the no-till system in the younger alleycrops.

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.

Balanço do nitrogênio e fósforo em solo com cultivo orgânico de hortaliças após a incorporação de biomassa de guandu

Os objetivos deste trabalho foram avaliar os efeitos de faixas de guandu (Cajanus cajan) e da incorporação da biomassa proveniente de sua poda na fertilidade do solo e na produtividade de três hortaliças sob cultivo orgânico. O delineamento usado foi de blocos casualizados completos em esquema de parcelas subsubdivididas com três repetições. As produtividades de beterraba, cenoura e feijão-de-vagem não foram afetadas pelos tratamentos. Nas parcelas onde não houve incorporação da biomassa de guandu, o balanço de nitrogênio no sistema foi negativo, ao passo que com a incorporação, esse balanço foi positivo. Embora tenha ocorrido balanço positivo para o fósforo nas parcelas sem a incorporação de biomassa de guandu, houve um aumento significativo na absorção desse elemento pelas hortaliças quando o material foi incorporado. O sistema de cultivo em aléias de guandu pode representar uma prática vantajosa para os produtores orgânicos, por contribuir na manutenção da fertilidade do solo.

Nitrogen mineralization in a pecan (Carya illinoensis K. Koch)?cotton (Gossypium hirsutum L.) alley cropping system in the southern United States

Information on temporal and spatial patterns of N mineralization is critical in designing tree-crop mixed systems that could maximize N uptake while minimizing N loss. We quantified N mineralization rates in a pecan (Carya illinoensis K. Koch)–cotton (Gossypium hirsutum L.) alley cropping system in northwestern Florida with (non-barrier) and without tree-crop belowground interactions (barrier separating the root systems of pecan and cotton). Monthly rates of mineralization were estimated using buried bag incubations over a 15-month period. In addition, seasonal mineralization rates and cotton lint yield on soils supplied with two sources of N—inorganic fertilizer and organic poultry litter—were assessed. Results indicated that temporal variations in net NH4 and NO3 accumulation and mineralization rates were driven primarily by environmental factors and to a lesser degree by initial soil NH4 and NO3 levels. Mineralization varied by belowground interaction treatment during the initial growing season, when the non-barrier treatment exhibited a higher mineralization rate than the barrier treatment, likely due to reduced nutrient uptake by cotton in the non-barrier or a higher degree of immobilization in the barrier treatment. Mineralization during the second growing season was similar for both treatments. Source of N had no effects on N transformation in the soil. Lint yield reductions were observed in the non-barrier treatment during both years compared to the barrier treatment, likely due to interspecific competition for water. Yield differences between treatments in the second growing season were likely compounded by a diminishing pre-study fallow effect. Source of N was found to have a significant effect on cotton yield, with inorganic fertilizer resulting in 39% higher lint compared to poultry litter in the barrier treatment.

Ex-ante economic analysis of alternative mulch-based management systems for sustainable plantain production in Southeastern Nigeria

Due to rapid loss of soil fertility in traditional cropping systems and subsequent yield decline, plantain fields in Southeastern Nigeria are usually reverted to fallow after three years. This study investigates the potential of mulch-based systems for long term plantain production: alley cropping with Dactyladenia barteri and natural bush, and a cut-and-carry technique with Pennisetum purpureum. Model results simulate yields decline observed under traditional cropping systems due to a decrease in soil fertility. The adoption of mulch-based technologies is conditioned by capital availability. However, when adequate capital is available, mulch-based systems are quite profitable. Under baseline conditions, the alley cropping system with natural bush outperforms the other two improved technologies with a 154% and 72% increase in net returns over continuous and shifting traditional systems, respectively. The traditional system had the worst performance without fertilizer use. A sensitivity analysis shows that the increase in net return due to fertilizer in the alley cropping and traditional systems is at least 25%. This analysis indicates that credit programs that reach small farmers and land reform that gives them secure title are essential to widespread adoption of mulch-based plantain systems.