Seeking an alternative to Sesbania spp. tree fallows, a Tephrosia species and provenance trial was conducted at Msekera Research Station, Chipata (Zambia) to evaluate eleven Tephrosia vogelii and three Tephrosia candida provenances. They were tested for biomass production, quality of biomass, resistance to root-knot nematodes, nitrogen release, and for their effects on soil nitrogen dynamics. At the end of 1.5 years, the T. candida provenances 02970, 02971 and 02972 from Madagascar produced two times greater amount of aboveground biomass than the T. vogelii provenances. There was little variability among the T. vogelii provenances in terms of litter and biomass production. Weed growth was significantly greater under T. vogelii than T. candida provenances. While Tephrosia vogelii provenance 98/02 from Zambia and T. candida 02972 were highly tolerant to the Meloidogyne incognita nematodes, T. vogelii provenances 02977, 98/03, 02973 from Kenya, Zambia and Malawi, respectively, were highly susceptible to the nematodes. The Tephrosia species and provenances showed a wide variability in terms of N, lignin and polyphenol concentration in their foliage. Mineralization of N in the foliage of T. candida provenances 02970 and 02971 and T. vogelii provenances 98/04 and 02974 from Malawi occurred rapidly within 14 weeks of incubation. At the end of the 2-year growth period, there was significantly greater total inorganic N under T. candida provenance 02972 (12.5 mg kg1) than T. vogelii (5 mg kg1) provenance Mungwi 98/02. Maize (Zea mays L.) yields after T. candida provenances were greater than those after T. vogelii provenances. Further testing of the most promising provenances is needed for their effects on subsequent maize yields under a range of farm conditions.
Tag: mineralization
Nitrogen mineralization in soils under grasses and under trees in a protected Venezuelan savanna
Nitrogen mineralization was evaluated in soils beneath the most common woody species growing isolated within the grass matrix of a Venezuelan Trachypogon savanna, which has been protected from fire and cattle grazing since 1961. Adult trees of three evergreen species, Byrsonima crassifolia (L) H. B. K., Curatella americana L., and Bowdichia virgilioides H. B. K; and two deciduous, Godmania macrocarpa Hemsley and Cochlospermun vitifolium (Wild) Spreng were selected. The amount of N mineralized (NH4+-N+NO3-N) during 15 weeks of laboratory incubation of soils collected from beneath trees, was significantly higher (p<0.01) than those from under grasses. Values of N mineralized on soil from under trees were from 21.28 to 82.65% greater than for soil from under grasses. A highly significant (p<0.01) positive correlation, for all soils, was found between Nm and SOC, and between Nm and Nt. The higher N mineralization rates under trees would reflect a higher soil biological activity, due to higher SOC and Nt, of the soils under the tree canopies than those under grasses. The N availability values obtained under all species reveal the importance these trees have for creating enriched areas on generally oligotrophic soils.Nitrogen mineralized in the soil from beneath evergreen trees was significantly (p<0.01) higher than from under deciduous trees, being 25.87% higher on average. Similarly to the relation found for all soils, a highly significant (p<0.01) positive correlation between Nm and SOC and between Nm and Nt was also obtained for soils beneath all trees, indicating the importance of SOC and Nt for nitrogen mineralization processes in this savanna. The higher SOC and Nt contents found under evergreen trees are probably due to the longer time they have been established on the site as compared to the deciduous ones.The chemical quality of fresh fallen leaves (as measured by their lignin/nitrogen ratio) did not seem to influence the quality of the SOM (as measured by C/N ratio), since the C/N ratio was not statistically different for the soils under the two groups of trees. Apparently, whatever the chemical quality of the fresh fallen leaves (higher lignin/nitrogen ratio in evergreen trees), the humification processes in this savanna soil environment seems to homogenize the SOM beneath both types of trees.
Tithonia diversifolia in western Kenya: relationship of tissue phosphorus concentration to soil phosphorus
Tithonia diversifolia, a shrub in the family Asteraceae, is widely distributed alongfarm boundaries in the humid and subhumid tropics of Africa. Green biomass of tithonia hasbeen recognized as an effective source of nutrients for lowland rice (Oryza sativa) in Asia andmore recently for maize (Zea mays) and vegetables in eastern and southern Africa. This paperreviews the potential of tithonia green biomass for soil fertility improvement based on recentresearch in western Kenya. Green leaf biomass of tithonia is high in nutrients, averaging about3.5% N, 0.37% P and 4.1% K on a dry matter basis. Boundary hedges of sole tithonia can produceabout 1 kg biomass (tender stems + leaves) m–1yr–1on a dry weight basis. Tithonia biomassdecomposes rapidly after application to soil, and incorporated biomass can be an effective sourceof N, P and K for crops. In some cases, maize yields were even higher with incorporation oftithonia biomass than with commercial mineral fertilizer at equivalent rates of N, P and K. Inaddition to providing nutrients, tithonia incorporated at 5 t dry matter ha–1can reduce P sorptionand increase soil microbial biomass. Because of high labor requirements for cutting and carryingthe biomass to fields, the use of tithonia biomass as a nutrient source is more profitable withhigh-value crops such as vegetables than with relatively low-valued maize. The transfer oftithonia biomass to fields constitutes the redistribution of nutrients within the landscape ratherthan a net input of nutrients. External inputs of nutrients would eventually be required to sustainproduction of tithonia when biomass is continually cut and transferred to agricultural land
Phosphorus management in tropical agroforestry: current knowledge and research challenges
Nitrogen mineralization and maize yields following application of tree prunings to a sandy soil in Zimbabwe
Despite the promotion of prunings as sources of nitrogen for crops, lack of synchronization between N mineralization from prunings and plant uptake remains a major limitation to the impact of prunings on crop yields. A laboratory and a field experiment were therefore carried out to determine the mineralization patterns of selected prunings and assess the potential that exists to improve synchrony by mixing prunings of different quality. The laboratory incubation experiment was conducted for 84 days to determine the C and N release patterns of prunings of different quality and the manipulation of the C and N mineralization trends by mixing prunings of different quality. High quality prunings were considered to be those with high CO2 evolution rates and mineralize N rapidly. The % C and % N released in 84 days were highest for the high quality prunings of Tithonia diversifolia (70% and 30% respectively) and least for the low quality prunings of Flemingia macrophylla (25% and –5% respectively). The medium quality prunings of Acacia angustissima and Calliandra calothyrsus had similar proportions of released C and N (about 40% C and 10% N). Different mixtures of T. diversifolia with other species showed contrasting influence on C release and N mineralization. Most mixtures released less C than that predicted, but in contrast most mixtures released N at a rate either matching or above the predicted. The % N released was strongly correlated with the polyphenol protein binding capacity (r2 = 0.53) and also with the % C released (r2 = 0.62). The field experiment was done for two cropping seasons to determine the effects of the prunings of these species and their mixtures on maize grain yield. The prunings were added at 5 t ha1 and incorporated into the top 15 cm by hand hoeing in the first season and their residual effects were monitored in the second season. Medium and low quality prunings produced significantly (p < 0.05) higher maize grain yields in the first season ranging between 2.4 t ha1 and 3.4 t ha1 compared with T. diversifolia which produced 1.7 t ha1. This suggested better synchrony in N release and uptake by maize with medium and low quality prunings compared with high quality prunings. The only mixture that indicated improved synchrony was the mixture of T. diversifolia and C. calothyrsus. This study showed that mixing prunings of different quality produce different patterns of N mineralization, some of which were unexpected and had a potential for improving N synchrony.
Multipurpose tree prunings as source of nitrogen to maize under semi-arid conditions in Zimbabwe: 3. Interactions of pruning quality, time and method of application. Agroforestry Systems
Decomposition- and N-mineralization rates of multipurpose tree prunings applied as a source of N to annual crops in agroforestry systems are affected by the chemical composition and method and time of application of the prunings and the soil type. In a greenhouse study undertaken on two contrasting Zimbabwean soils, there was a significant interaction of pruning quality with time and method of pruning application on nitrogen recovery by maize and residual effects on a subsequent maize crop on both soil types. Incorporating prunings in the soil at planting gave higher nitrogen recovery compared to surface application at two or four weeks after planting for all three MPT species used.Flemingia macrophylla showed prolonged N immobilization on an Alfisol (sandy clay loam) but not on the Psamment (sandy soil). Nitrogen recovery by the second maize crop (residual effect) was influenced by pruning quality, time of application, and soil type. Low-quality prunings such asFlemingia macrophylla andAcacia angustissima applied four weeks after planting gave higher residual effect on N recovery on the Alfisol than on the Psamment (3% vs. 6%).
Decomposition rates of legume residues and N-mineralization in an ultisol in Lampung
Alley cropping of maize with calliandra and leucaena in the subhumid highlands of Kenya: Part 2. Biomass decomposition, N mineralization, and N uptake by maize
A major challenge in developing agroforestry approaches that utilize tree-leaf biomass for provision of N to crops is to ensure synchrony between the N released from decomposing prunings and N demand by crops. A study was conducted in the subhumid highlands of Kenya to assess the rate of decomposition and mineralization of soil-incorporated Calliandra calothyrsus Meissner (calliandra) and Leucaena leucocephala (Lam.) de Wit (leucaena) tree biomass and maize roots (Zea mays L.) both in an alley cropping and a sole cropping system. The amount of mineralized N peaked four weeks after planting (WAP) maize in all the treatments during both seasons of 1995. Cumulative mineralized N at week 20 ranged from 114 to 364 kg N ha1 season1, the absolute control treatment giving the lowest and the prunings-incorporated treatments giving the highest amounts in the two seasons. Total N uptake by maize, ranging from 42 to 157 kg ha1 season1, was lowest in the ‘alley-cropped, prunings-removed’ treatments, and highest in the ‘non alley-cropped-prunings-incorporated’ treatments. The apparent N recovery rate by maize was highest in the fertilizer applied treatments in the two seasons. Decomposition rate constants (kD) ranged from 0.07 to 0.21 week1, and the rates among the different plant residues were as follows: leucaena < calliandra < maize roots. Nitrogen release rate constants (kN), ranging from 0.04 to 0.25 week1, followed a similar pattern as the rate of decomposition with leucaena releasing the highest amount of N followed by calliandra and lastly by maize roots
Short-term patterns of carbon and nitrogen mineralisation in a fallow field amended with green manures from agroforestry trees
The mineralisation of green manure from agroforestry trees was monitored with the objective to compare the temporal dynamics of mineralisation of litter from different species. Green manures from five agroforestry tree species were used on a fallow field during the long rainy season of 1997 (March–August) and from two species in the following short rainy season (September–January) in western Kenya. Different methods, i.e. measurements of isotopic ratios of C in respired CO2 and of soil organic matter (SOM) fractions, soil inorganic N and mass loss from litterbags, were used in the field to study decomposition and C and N mineralisation. Soil respiration, with the separation of added C from old soil C by using the isotopic ratio of 13C/12C in the respired CO2, correlated well with extractable NH4+ in the soil. Mineralisation was high and very rapid from residues of Sesbania sesban of high quality [e.g. low ratio of (polyphenol+lignin)/N] and low and slow from low quality residues of Grevillea robusta. Ten days after application, 37% and 8% of the added C had been respired from Sesbania and Grevillea, respectively. Apparently, as much as 70–90% of the added C was respired in 40 days from high quality green manure. Weight losses of around 80%, from high quality residues in litterbags, also indicate substantial C losses and that a build-up of SOM is unlikely. For immediate effects on soil fertility, application of high quality green manure may, however, be a viable management option. To achieve synchrony with crop demand, caution is needed in management as large amounts of N are mineralised within a few days after application.
Changes in soil properties and their effects on maize productivity following Sesbania sesban and Cajanus cajan improved fallow systems in eastern Zambia
Improved fallows with leguminous trees have been developed in Southern Africa as a viable alternative to inorganic fertilizers but the changes in soil properties that are responsible for crop productivity improvement and implications of mixing litter and fresh leaves from the same tree species on soil fertility are not fully understood. Our objectives were to quantify (1) some changes in soil properties that are responsible for crop production improvement under improved fallow systems; (2) the N mineralization patterns of mixtures of litter and fresh leaves from the same tree species. The treatments used in the study were 2-year planted Sesbania sesban (sesbania) and Cajanus cajan (cajanus) and controls of natural fallow, continuous fertilized and unfertilized maize. At fallow clearing sesbania contributed 56 kg N ha1 through litter and fresh leaves. Sesbania (fresh leaves + litter) showed high N mineralization after 10 weeks compared to the mixture of cajanus fresh leaves with litter. Maize yields were significantly correlated with preseason NO3-N and total inorganic-N content of the top 20-cm soil layer. Soil penetrometer resistance at 4 weeks after planting was lowest in the sesbania land-use system (2.2 Mpa), whereas the highest percentage of water-stable aggregates at fallow clearing and crop harvest was in sesbania (83%) and cajanus (77%), respectively. The improved soil conditions and N contribution of sesbania and cajanus fallows to the subsequent maize crop was evidenced by increased maize yields of between 170–200% over maize without fertilizer.