l Department of Biological Sciences, Wye College, University of London, Wye, Ashford, Kent TN25 5AH UK* and. 2 Fakultas Pertanian, Universitas Brawijaya, ...
Plantand Soil 176: 149-160, 1995. (~) 1995KluwerAcademicPublishers. Printedin the Netherlands.
Manipulation of quality and mineralization of tropical legume tree prunings by varying nitrogen supply E. Handayanto 1'2, G. C a d i s c h 1 and K.E. Giller 1 l Department of Biological Sciences, Wye College, University of London, Wye, Ashford, Kent TN25 5AH UK* and 2Fakultas Pertanian, Universitas Brawijaya, Malang 65145, Indonesia Received4 November1994.Acceptedin revisedform28 April 1995 Key words: Calliandra calothyrsus, Gliricidia sepium, leaching, lignin, mineralization rate constant, polyphenois, protein-binding capacity, leaching, JSN nitrogen recovery
Abstract The effect of N supply on the quality of Calliandra calothyrsus and Gliricidia sepium prunings was studied in a glasshouse over a 7-month growing period. Increasing the concentration of N supplied from 0.625 to 10.0 mM NO3-N resulted in increased N concentration but decreased polyphenol concentration, protein-binding capacity and C:N ratio of prunings from both species. Lignin concentration was not consistently altered by the N treatment. Mineralization of N from the prunings was measured over a 14-week period under controlled leaching and nonleaching conditions. The results indicated a strong interaction between legume species and concentration of N supply in their influence on N mineralization of the prunings applied to the soil. Differences in the %N mineralized were dictated by the quality of the prunings. The (lignin + polyphenol):N ratio was the pruning quality factor which could be used most consistently and accurately to predict N mineralization of the legume prunings incubated under leaching conditions, and the relationship was best described by a linear regression. Under non-leaching conditions, however, the protein-binding capacity appeared to be the most important parameter in determining the patterns of N release from the prunings studied. The relationship between the N mineralization rate constant and the protein-binding capacity was best described by a negative exponential function, y = 0.078 exp(-0.0083x). The present study also indicated that the release of N from legume prunings containing a relatively high amount of polyphenol could be enhanced by governing the N availability conditions under which the plant is grown, for example whether or not it is actively fixing nitrogen. Estimates of pruning N mineralization after 14 weeks with the difference method averaged 6% (leaching conditions) and 22% (nonleaching conditions) more than with the 15N method for all legume prunings studied. The recovery of pruning by maize (4-38%) was well correlated with the % pruning N mineralized suggesting that incubation data closely reflect the pruning N value for a given catch crop under non-leaching conditions.
Introduction Apart from the direct economic products of leguminous trees used in agroforestry systems, the main functions of the trees are to maintain soil fertility by controlling erosion, by nutrient recycling from deeper soil layers and by providing soil organic matter. A major consideration for the selection of leguminous trees for such systems is the rate and amount of N mineralized from the prunings and hence the N benefit obtained by * FAXno correspondingauthor:+ 44 1233813320
crops. The rate of N mineralization of a specific type of plant residue is largely determined by the chemical and physical nature of the residue itself, known as its 'quality' (Swift and Sanchez, 1984). Factors contributing to the high quality (i.e. rapid decomposability) are high N concentrations, low lignin concentrations and low polyphenol concentrations (Haynes, 1986). Several researchers have stressed the importance of initial N concentration on N release from plant materials (e.g, Frankenberger and Abdelmagid, 1985; Iritani and Arnold, 1960). However, when plant materials contain
150 a high concentration of lignin, the lignin exerts more control on the overall rate of decomposition than does N (Fox et al., 1990; Kachaka et al., 1993). Palm and Sanchez (1991) attributed differences in N mineralization patterns of various tropical legumes to polyphenols in the legume leaves, and showed that the polyphenol:N ratio was a good predictor of N mineralization. Handayanto et al. (1994) demonstrated that variation in nitrogen release patterns among different legume tree prunings were strongly related to differences in (lignin + polyphenol):N ratio and protein-binding capacity of polyphenols in the prunings. However, when comparing the decomposition of prunings from several different species, several quality factors, including physical structure, vary at the same time so that the determination of key factors regulating decomposition is difficult. Therefore we tried a different approach in which the quality of residues of a species was manipulated. In order to manipulate quality of residues, two legume tree species (Calliandra calothyrsus and Gliricidia sepium) were fertilized with varying rates of NOa-N. The decomposition and nitrogen mineralization behaviour of prunings of the two species were then tested upon application to the soil. The two legume tree species were chosen because of the different quality of their prunings produced under field conditions.Calliandra calothyrsus had been reported to have high nitrogen and polyphenol concentrations, whereas Gliricidia sepium had a low polyphenol but high nitrogen concentrations (Brewbaker, 1989; Handayanto et al., 1994; Little et al., 1988). In earlier experiments we found implications that the activity of soluble polyphenols, reflected in their ability to bind protein, was more closely related to the rate of N mineralization than the total polyphenol concentration (Handayanto et al., 1994). The importance of this protein-binding capacity of the polyphenols appeared to be more pronounced under non-leaching conditions. Therefore in the work reported here measurements of N mineralization were carried out both under controlled leaching and non-leaching conditions. To test the relevance of incubation data on N availability for a growing crop we also conducted a growth room experiment to measure recovery by maize of the N which was released from the prunings of different quality.
Materials and methods
Experiment 1: Effect of N supply on quality of legume tree prunings Three pre-germinated seeds of each species of either Calliandra calothyrsus or Gliricidia sepium were planted in 15 cm diameter plastic pots containing perlite and placed in a glasshouse at Wye College from February to September 1992 with supplementary light at night from February to May 1992. To prevent nodulation, the pots were previously disinfected by immersing in 1% sodium hypochlorite solution for 3 days with the aim of keeping the plants free from rhizobia. Each species was grown under five N concentrations supplied as K~sNO3 5.31% atom excess: 0.625, 1.25, 2.5, 5.0 and 10.0 mM, supplied in solution at the rate of 50400 mL day-l pot-L according to demand. Nitrogen was applied together with other macro- and micronutrients (Ca, K, F, S, M CI, Fe, Mn, Zn, B, Mo and Co, modified from Hammer et al., 1978) to ensure that the latter were not limiting. To prevent salt accumulation in the pots they were flushed with deionised water at weekly intervals. The experiment was laid out in a randomized block design consisting of five treatments (N concentration in the nutrient solution) of each species with four replicates. The trees were pruned after 7 months growth. The prunings were weighed and oven dried at 60°C for 72 hours.
Experiments 2 and 3: Incubation of legume tree prunings soils under leaching and non-leaching conditions N mineralization behaviour of legume tree prunings (mixed leaves and fine stems (dia.
