Didik Suprayogo

Root distributions partially explain 15N uptake patterns in Gliricidia and Peltophorum hedgerow intercropping systems

The relative distributions of tree and crop roots in agroforestry associations may affect the degree of complementarity which can be achieved in their capture of below ground resources. Trees which root more deeply than crops may intercept leaching nitrogen and thus improve nitrogen use efficiency. This hypothesis was tested by injection of small doses of (15NH4)2SO4 at 21.8 atom% 15N at different soil depths within established hedgerow intercropping systems on an Ultisol in Lampung, Indonesia. In the top 10 cm of soil in intercrops of maize and trees, root length density (Lrv) of maize was greater than that of Gliricidia sepium trees, which had greater Lrv in this topsoil layer than Peltophorum dasyrrachis trees. Peltophorum trees had a greater proportion of their roots in deeper soil layers than Gliricidia or maize. These vertical root distributions were related to the pattern of recovery of 15N placed at different soil depths; more 15N was recovered by maize and Gliricidia from placements at 5 cm depth than from placements at 45 or 65 cm depth. Peltophorum recovered similar amounts of 15N from placements at each of these depths, and hence had a deeper N uptake distribution than Gliricidiaor maize. Differences in tree Lrv across the cropping alley were comparatively small, and there was no significant difference (P<0.05) in the uptake of 15N placed in topsoil at different distances from hedgerows. A greater proportion of the 15N recovered by maize was found in grain following 15N placement at 45 cm or 65 cm depth than following placement at 5 cm depth, reflecting the later arrival of maize roots in these deeper soil layers. Thus trees have an important role in preventing N leaching from subsoil during early crop establishment, although they themselves showed a lag phase in 15N uptake after pruning. Residual 15N enrichment in soil was strongly related to application depth even 406 days after 15N placement, demonstrating the validity of this approach to mapping root activity distributions.

Nitrogen use efficiency of monoculture and hedgerow intercropping in the humid tropics

The design of productive and efficient intercropping systems depends on achieving complementarity between component species’ resource capture niches. Spatiotemporal patterns of capture and use of pruning and urea nitrogen (N) by trees and intercrops were elucidated by isotopic tracing, and consequences for nitrogen use efficiency were examined. During the first cropping season after applying urea−15N, maize accounted for most of the plant 15N recovery in Peltophorum dasyrrachis (33.5%) and Gliricidia sepium (22.3%) hedgerow intercropping systems. Maize yield was greatest in monoculture, and maize in monoculture also recovered a greater proportion of urea 15N (42%) than intercropped maize. Nitrogen recovery during active crop growth will not be increased by hedgerow intercropping if hedgerows adversely affect crop growth through competition for other resources. However, hedgerows recovered substantial amounts of 15N during both cropping cycles (e.g. a total of 13–22%), showing evidence of spatio-temporal complementarity with crops in the spatial distribution of roots and the temporal distribution of Nuptake. The degree of complementarity was species-specific, showing the importance of selecting appropriate trees for simultaneous agroforestry. After the first cropping season 17–34% of 15N applied was unaccounted for in the plant-soil system. Urea and prunings N were recovered by hedgerows in similar amounts. By the end of the second (groundnut) cropping cycle, total plant 15N recovery was similar in all cropping systems. Less N was taken up by the maize crop from applications of labelled prunings (5–7%) than from labelled urea (22–34%), but the second crop recovered similar amounts from these two sources, implying that prunings N is more persistent than urea N. More 15N was recovered by the downslope hedgerow than the upslope hedgerow, demonstrating the interception of laterally flowing N by hedgerows.

Agroforestation of Grasslands in Southeast Asia: WaNuLCAS Model Scenarios for Shade-Based Imperata Control During Tree Establishment

In the stage of land use evolution where smallholder tree-based systems are desirable as replacement of Imperata cylindrica (and similar) grasslands, agroforestry can provide a gradual and rewarding approach to the transition. There tends to be, however, a gap between the last opportunity for food crop interplanting and canopy closure providing shade-based control of grass and weed growth. In such period, regrowth of Imperata enhances the risk of fire and failure of tree establishment. We analyzed the duration of this ‘Imperata regrowth window’, for a range of planting patterns and choice of tree species in Lampung (Indonesia) and northern Mindanao (the Philippines). Simulations of agroforestation scenarios with the WaNuLCAS model (‘water, nutrient and light capture in agroforestry systems’) focuss on the Imperata regrowth window as the period between 50 percent and 15 percent of ground-level light availability.

Effect of Plant Residues Application on Nitrogen Release From Plant Residues Previously Added

This study was carried to effect of plant residues application on nitrogen release from plant residues previously added (rice straw=RS; soybean=SY) with 15 N isotope dilution technique on growth of maize with application of Twelve treatments (six treatments of addition of new plant residues and six treatments of no addition of new plant residues were arranged in a randomized block design with three replicates for each treatment resulting total of 36 pots. Five pre-germinated seeds of maize were planted in each pot and thinned to four plants after 1 week. six types of 15 N labelled plant residues, i.e. biomass of rice grown under 0.0625mM N (N1T1), 0.250 mM N (N2T1), 10.0 mM N (N3T1) supplies, and biomass of soybean grown under 0.0625 mM N (N1T2), 0.250 mM N (N2T2), 10.0 mM N (N3T2) supplies. Fresh plant residue (unlabelled 15 N) used for this study was obtained by growing rice and soybean for 2 months under 10.0 mM N supplied as CO(NH2)2 in solution at the rate of 400 ml/pot/day. Soils (10 kg) from each pot of experiment previously conducted were split into two parts. The first part of 5 kg of soil was treated with addition of new plant residues accordingly (unlabelled rice residue and soybean residue, supplied with 10 mM N for 3 months). This treatment was aimed to examine the influence of addition of new plant residues on N release from previously added 15 N-labelled plant residues and N uptake by maize. No new plant residue was added to the second part of 5 kg of soil. This treatment was aimed to evaluate the residual N release from previously added 15 N-labelled plant residues and N uptake by maize. This study concluded that rice straw residues amendment affect the soil fertility more than soybean residues sufficiently to improve growth of the subsequent crop.