Kurniatun Hairiah

Auger Sampling, Ingrowth Cores and Pinboard Methods

This chapter outlines those methods for assessing root systems structure and function in the field which are based on washing roots free from the soil in which they grew. Some of these methods are included in previous reviews (Kolesnikov 1971; Bohm 1979). The methods are either disruptive or totally destructive to the root system being studied and to the immediate environment (Taylor et al. 1991).

Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths

Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses we placed highly enriched 15N-labelled ammonium sulphate at three depths in the soil between mixed hedgerows of the shallow-rooting Gliricidia sepium and the deep rooting Peltophorum dasyrrhachis. A year after the isotope application most of the residual 15N in the soil remained close to the injection points due to the joint application with a carbon source which promoted 15N immobilization. Temporal 15N uptake patterns (two-weekly leaf sub-sampling) as well as total 15N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little 15N from any depth but obtained an estimated 44–58% of its N from atmospheric N2-fixation. Gliricidia took up an estimated 21 kg N ha–1 and Peltophorum an estimated 42 kg N ha–1 from beneath the main crop rooting zone. The results demonstrate that direct placement of 15N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments.

Old tree root channels in acid soils in the humid tropics: Important for crop root penetration, water infiltration and nitrogen management

Under high rainfall conditions on acid soils with shallow crop root systems the rate of N leaching is high. A simple model predicts nitrogen uptake efficiency as a function of the amount of rainfall in excess of evapotranspiration, rooting depth and degree to which N leaching is retarded in comparison with water transport. Field observations on acid soils in S.E. Nigeria and S. Sumatera (Indonesia) showed that this model should be amended to include the role of old tree root channels. Crop roots can follow these channels, which are coated with partly decayed organic matter, into the acid subsoil. Measurements of water infiltration with a Guelph permeameter and a methylene blue dye showed that such channels form the major infiltration sites during rainstorms. Implications for nitrogen use efficiency and cropping pattern are discussed.

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 availability and soil N2O emissions following conversion of forests to coffee in southern Sumatra

[1]xa0Changes in land use impact on the N cycle with both local and global consequences. We examined how conversion of forest to agriculture in one catchment in southern Sumatra altered N availability and soil N2O emission. Measurements were made along a chronosequence of forest land converted to coffee gardens. A number of different management practices were also examined. Inorganic N stocks and N cycling rates were highest in the forest and lower in the coffee gardens. The forest and young conversion sites appeared to be N limited, whereas the older agricultural sites and the more intensively managed sites were not as strongly N limited. N2O emissions were low in the forest (<2 kgN ha−1yr−1) and increased sharply following deforestation. Emissions on recently cleared land were 4.6 kgN ha−1yr−1 and 8.4 kgN ha−1yr−1 in a 1-year-old coffee garden. Emissions in the older coffee gardens were lower with the lowest flux observed in a 10 year old site (1.8 kgN ha−1yr−1). We explored the effects of different types of management approaches that farmers are using in this landscape. Emissions in an 18-year-old multistrata coffee garden with a significant overstory of N fixing trees were 5 times greater (15.5 kg ha−1yr−1) than emissions from forests. We also found that intensive organic matter management produced high emissions. To understand the spatial and temporal variability of the N2O emissions we used the hole-in-the-pipe conceptual model. N2O fluxes were lowest on N limited sites. Soil water content also played an important role and emissions were highest when water filled pore space (WFPS) was between 85 and 95%. A number of formulations of this model have been applied in different ways over the years to explain spatial and temporal variation in the soil N-oxide flux, and in this study we found the mechanistic explanation useful. Our study suggests that land use change and intensification of agriculture in N limited highland landscapes may significantly increase the biosphere to atmosphere flux of N gases.

Food-crop-based production systems as sustainable alternatives for Imperata grasslands?

Purely annual crop-based production systems have limited scope to be sustainable under upland conditions prone to infestation by Imperata cylindrica if animal or mechanical tillage is not available. Farmers who must rely on manual cultivation of grassland soils can achieve some success in suppressing Imperata for a number of years using intensive relay and intercropping systems that maintain a dense soil cover throughout the year, especially where leguminous cover crops are included in the crop cycle. However, labour investment increases and returns to labour tend to decrease in successive years as weed pressure intensifies and soil quality declines.Continuous crop production has been sustained in many Imperata-infested areas where farmers have access to animal or tractor draft power. Imperata control is not a major problem in such situations. Draft power drastically reduces the labour requirements in weed control. Sustained crop production is then dependent more solely upon soil fertility management. Mixed farming systems that include cattle may also benefit from manure application to the cropped area, and the use of non-cropped fallow areas for grazing. In extensive systems where Imperata infestation is tolerated, cassava or sugarcane are often the crops with the longest period of viable production as the land degrades.On sloping Imperata lands, conservation farming practices are necessary to sustain annual cropping. Pruned tree hedgerows have often been recommended for these situations. On soils that are not strongly acidic they may consistently improve yields. But labour is the scarcest resource on small farms and tree-pruning is usually too labour-intensive to be practical. Buffer strip systems that provide excellent soil conservation but minimize labour have proven much more popular with farmers. Prominent among these are natural vegetative strips, or strips of introduced fodder grasses.The value of Imperata to restore soil fertility is low, particularly compared with woody secondary growth or Compositae species such as Chromolaena odorata or Tithonia diversifolia. Therefore, fallow-rotation systems where farmers can intervene to shift the fallow vegetation toward such naturally-occurring species, or can manage introduced cover crop species such as Mucuna utilis cv. cochinchinensis, enable substantial gains in yields and sustainability. Tree fallows are used successfully to achieve sustained cropping by some upland communities. A variation of this is rotational hedgerow intercropping, where a period of cropping is followed by one or more years of tree growth to generate nutrient-rich biomass, rehabilitate the soil, and suppress Imperata. These options, which suit farmers in quite resource-poor situations, should receive more attention.

Forest Soils under Alternatives to Slash and Burn Agriculture in Sumatra, Indonesia

A global project on ‘Alternatives to Slash and Burn’ agriculture was initiated by a consortium of international and national research institutes to facilitate intensification of the use of converted forest land, in order to help alleviate poverty and protect the remaining forest areas for their biodiversity values and their role in mitigating greenhouse gas emissions.

Nitrogen supply from rotational or spatially zoned inclusion of Leguminosae for sustainable maize production on an acid soil in Indonesia

On acid upland soils in the humid tropics, the combination of high leaching rates and shallow rooted crops may lead to low efficiencies of N use. Sustainability of crop production in this zone depends on either large amounts of external inputs, or on maximising efficiency of the use of local as well as small amounts of external resources. Additional sources of soil organic matter can be obtained by including leguminous cover crops in a rotational system or by spatially zoned systems, with a permanent presence of trees. In view of the high leaching rates, spatially zoned systems with deep-rooted trees may be more effective.

Crop yield, C and N balance of three types of cropping systems on an Ultisol in Northern Lampung

Three types of cropping systems, cassava-based intercropping, hedgerow intercropping and legume cover crop rotations, were evaluated in 1994-1997 in Northern Lampung, Sumatra (Indonesia). The C and N flows returned within and transported out of plots and crop yields of different cropping systems were quantified. Cassava-based systems were not stable and yields declined over time. Intercropping cassava with rice increased cassava fresh tuber weight by 5-48% compared to the monocropping system. The hedgerow intercropping gave lower maize, rice, groundnut and cowpea yields than could be obtained in a crop rotation with legume cover crops. Maize grain yields in the 80-20 rice/maize mixture were ~ 0.4 t ha-1 in the rice - groundnut rotation and about half as much when intercropped with cassava or hedgerows. Rice yields intercropped with cassava or with hedgerows were ~1 t ha-1 less in year 2 and 3 than those grown in rotation with groundnut. The rice yield in the first cropping season was only ~1 t ha-1, but in the second and third year yields in the rice - legume rotation increased to ~2 and 3 t ha-1, respectively. This increase occurred despite a decline in soil organic matter content. The cassava-based systems removed much more C (7 t ha-1 yr-1) than the other systems, while less was returned (~0.5-2 t ha-1) to the soil. In the hedgerow intercropping system ~2.5 t C ha-1 yr-1 was returned to the plot as biomass pruning and crop residues and ~1.5 t C ha-1 yr-1 was removed from the plot as yield. In the cover crop rotation 2.6 t C ha-1 yr-1 was returned to the plot as crop residues plus Mucuna (only the 2nd year) and cowpea biomass, and ~1.1 t ha-1 yr-1 was removed from the plot. The hedgerow intercropping systems gave an N surplus of ~15-50 kg ha-1 yr-1 returned to the soil; while the balance was 10-20 kg ha-1 yr-1 for the cover crop rotation systems, and the cassava-based systems showed a negative N budget of ~60 kg ha-1 yr-1.

Plant functional types and traits as biodiversity indicators for tropical forests: two biogeographically separated case studies including birds, mammals and termites

Multi-taxon surveys were conducted in species-rich, lowland palaeotropical and neotropical forested landscapes in Sumatra, Indonesia and Mato Grosso, Brazil. Gradient-directed transects (gradsects) were sampled across a range of forested land use mosaics, using a uniform protocol to simultaneously record vegetation (vascular plant species, plant functional types (PFTs) and vegetation structure), vertebrates (birds, mammals) and invertebrates (termites), in addition to measuring site and soil properties, including carbon stocks. At both sites similar correlations were detected between major components of structure (mean canopy height, woody basal area and litter depth) and the diversities of plant species and PFTs. A plant species to PFT ratio [spp.:PFTs] was the best overall predictor of animal diversity, especially termite species richness in Sumatra. To a notable extent vegetation structure also correlated with animal diversity. These surrogates demonstrate generic links between habitat structural elements, carbon stocks and biodiversity. They may also offer practical low-cost indicators for rapid assessment in tropical forest landscapes.