Rod Lefroy

Indicators for sustainable land management based on farmer surveys in Vietnam, Indonesia, and Thailand

Abstract The current pressure on land resources necessitates the development of sustainable land management (SLM) systems. The process of developing such systems requires that methods are available to assess sustainability easily. Indicators of SLM need to include indicators of soil quality and land quality, but in addition they must take account of the environmental setting and include the more human aspects of land management: the social, economic and political aspects. Three case studies were undertaken to assess the sustainability of different land management systems practised by farmers on sloping lands of Indonesia, Thailand and Vietnam. Using the framework for evaluating sustainable land management (FESLM), detailed socio-economic and biophysical surveys were undertaken of 53 farms. The surveys aimed to characterise the land management systems, outline their constraints and potentials, and identify indicators and thresholds of sustainability in line with the five pillars of sustainability in the FESLM: productivity, security, protection, viability, and acceptability. The data were used to develop a suite of SLM indicators, with associated thresholds. These indicators have been included in a prototype decision support system (DSS). Feedback on the indicators was obtained from the farmers after the DSS was used to evaluate their farming systems. The indicators are highly specific as well as simplified, but they make a useful first step towards the development of a more generic system for evaluating SLM and for more accurate site specific and integrated evaluation. Evaluation of this structured and systematic approach yielded encouraging results in a separate study in Nepal.

Managing legume leys, residues and fertilisers to enhance the sustainability of wheat cropping systems in Australia 2. Soil physical fertility and carbon

Soil organic matter (SOM) is considered as a key indicator of sustainability, therefore measurements of SOM changes under various forms of management are needed for the development of sustainable systems. Because the measurement of total SOM is not sensitive enough to monitor short and medium term changes, techniques that measure meaningful fractions of SOM should be used. In this study both total carbon (CT) measured by combustion and labile carbon (CL) determined by oxidation with 333 mM potassium permanganate (KMnO4) were measured. Field trials, consisting of a legume phase followed by three wheat (Triticum aestivum L. cv. Janz) crops, were established on a degraded Ferric Luvisol (Red Earth) soil in New South Wales to investigate the effect of crop residue and fertiliser management on wheat yield, soil physical properties and SOM. Total and labile C increased following a lucerne (Medicago sativa L. cv. Trifecta) phase, however, chickpea (Cicer arietinum L. cv. Amethyst), barrel medic (Medicago truncatula L. cv. Sephi) and fallow leys resulted in no increases in soil C concentrations. During the wheat phase the concentration of CL significantly increased on the treatments with wheat stubble retention. This resulted in the C Management Index (CMI), an index comparing changes in labile and total C fractions relative to an uncropped reference soil, increasing from 19 to 27. The greatest treatment effect on soil physical properties was the retention of wheat stubble on the soil surface over the summer fallow period which increased hydraulic conductivity (K) by more than 65%, relative to the stubble removed treatment. Mean weight diameter (MWD) increased from 799 to 920 mm and a significant relationship was found between hydraulic conductivity and water stable aggregates >500 mm. Soil strength at 15 cm decreased from 2713 in the non-return to 2064 kPa in the stubble retained treatments with both treatments having a similar water content at the time of measurement. Although legume species are widely used as a rotation phase, their use in combination with cereal stubble retention is more likely to improve the overall fertility of the farming system. # 2000 Elsevier Science B.V. All rights reserved.

Managing legume leys, residues and fertilisers to enhance the sustainability of wheat cropping systems in Australia: 1. The effects on wheat yields and nutrient balances

Farming activities practiced on many Australian soils have resulted in substantial losses of soil organic matter (SOM), nutrient loss, soil structural degradation and declines in cereal yield and quality. Field trials, consisting of a legume or fallow phase followed by three wheat (Triticum aestivum L.) crops, were established on a degraded Ferric Luvisol (Red Earth) soil in New South Wales to investigate the effect of crop residue and fertiliser management on wheat yield and nutrient balances. There were no effects of a chickpea (Cicer arietinum L. cv Amethyst), barrel medic (Medicago truncatula L. cv Sephi), or fallow phase on the grain yields of three subsequent wheat crops. Grain yield was depressed by 12% following a lucerne (Medicago sativa L. cv Trifecta) crop from which the plant residues had been removed, relative to when residues were returned or grazed. Consecutively, higher wheat grain yield losses of 7.4 and 8.6% in 1994 and 1995 were found on treatments from which wheat stubble was annually removed from the system. Grain yield losses of 6, 7 and 13% in three consecutive wheat crops were found where no fertiliser was applied at sowing. Nutrient balances, based on inputs of nutrients in fertilisers and residues, and the export of nutrients in grain and crop residue were found to be useful in describing the flow of nutrients in a farming system and predicting possible soil nutrient depletion. Fallow systems provide no nutrient inputs and result in N losses of up toˇ189 kg ha ˇ1 over three wheat crops. The balance of nutrients such as potassium (K), which are contained in larger proportions in stubble, were found to beˇ102 kg ha ˇ1 on the wheat stubble removed treatments anda 8k g ha ˇ1 on the stubble retained treatments. Better recycling of crop residues and improving ley system to increase nutrient and C inputs have the potential to improve soil fertility and grain production. # 2000 Elsevier Science B.V. All rights reserved.

Measurement of decomposition and associated nutrient release from straw (Oryza sativa L.) of different rice varieties using a perfusion system.

Maintenance of soil carbon concentrations and synchronisation of nutrient release from crop residues to match crop demand is important if soil organic matter levels are to be maintained and nutrients are to be recycled efficiently. Two laboratory perfusion experiments were conducted to study the decomposition and nutrient release rates from straw of different rice varieties (Oryza sativa L.) which were collected from the field. Cumulative evolution of CO2 and nutrient release from the straw of 20 rice varieties was measured over a 6-week period. The CO2 release rate differed between varieties with the peak of CO2 release varying from 2 to 4 days. After 42 days, the percentage of C released from the straw ranged from 15.4% in variety PSBRc18 to 38.4% in variety Soc Nau. There was an inverse relationship (r2=0.60) between cumulative C release and C:N ratio and a direct relationship (r2=0.62) between digestible organic matter (DOM) and cumulative C release. A Straw Quality Index (SQI) was developed to describe the decomposition rate of the rice straw as follows:SQI= -56.85+(11.68 × % N) + (1.25 × % DOM) +(2.59 × % lignin) r2 = 0.81These findings indicate that SQI has a potential in assessing the quality of straw residue materials in predicting their usefulness in crop-residue management systems. Varieties, Soc Nau, IR67962 and PSBRc18, were used in a second perfusion experiment to determine C and nutrient release at 5, 10 and 20 days under aerobic and anaerobic conditions. Despite a two-fold difference between varieties in the amount of C evolved over 20 days, the proportion of nutrient release did not differ significantly between them. When perfusion was performed under anaerobic conditions, there were 45, 32 and 27% reductions in C evolution compared to aerobic conditions from Soc Nau, IR67962 and PSBRc18, respectively, but no differences in the proportion of N, P, S, K Mg and Na released between the aeration systems. These results indicate that under flooded conditions, depletion of O2 decreases decomposition rate of straw but the initial rate of nutrient release is unaffected. This uncoupling of C and nutrient release appears to be related to the more labile components of the nutrients present in the plants and their physiological role.

Tracing the nitrogen, sulfur, and carbon released from plant residues in a soil/plant system

Matching plant residue mineralisation rate to plant nutrient demand is one way of increasing the efficiency of nutrient cycling. A glasshouse experiment was conducted in a Soloth soil with a C4d13 C signature using drained pots to examine the effect on the yield of Japanese millet (Echinochloa frumentocea) and the fate of 15 N, 35 S, and C (using d 13 C shift) from the C 3 plants Flemingia macrophylla, Medicago truncatula hay, and wheat (Triticum aestivum) straw applied at 3 t/ha in the presence of N and NPKS fertiliser. The yield of Japanese millet at 91 days was highest where medic hay had been added (13.7 g/pot) and lowest where wheat straw was used (11.5 g/pot). Recovery of 35 S by the millet was highest in the wheat straw and medic hay treatments (mean 11.5%), whilst recovery of 15 N was highest from medic hay (15.8%). Leaching losses of 35 S were highest in the Flemingia and medic treatments (mean 8.1%), and 15 N loss in leachate was highest in the medic hay treatment (6.6%). A maximum of 1.5% of the C added in residues was recovered in the leachate of the medic hay treatment.

Diet selection and productivity of sheep grazing contrasting pastures

A grazing experiment was conducted at the Big Ridge 2 site CSIRO, Chiswick (30˚31′S, 151˚39′E), 20 km south of Armidale, New South Wales, Australia. The site was established in 1955. In March 1966, phalaris and white clover were sown and pastures were fertilised annually with superphosphate until 1993. There were 3 pasture treatments, each with 2 replicates: degraded pasture (low phalaris content), phalaris-dominant, and phalaris–white clover. The effect of pasture type on animal production (liveweight gain and wool) was only significant in 1996, when there were large differences in pasture composition and production between the 3 pasture types. n-Alkane based estimates showed that pasture degradation affected diet selection and nutrient intake and thus sheep production. The estimates in this study also showed no clear preference for a single pasture species over time and lack of strong preferential selection for clovers when sheep were grazing 3 contrasting pastures. Preferential selection of a particular species varied over time depending on the presence and availability of alternative species. Although there were large differences in total N and S intake and faecal output between the 3 pastures, the proportion of the dietary nutrient used for production was similar. This observation reveals the importance of further improving pasture and grazing management, particularly in productive phalaris–white clover pasture with high nutrient flux, to improve nutrient recycling through plant uptake and retention by animals in the grazing ecosystem, and reduce losses.

Measurement of decomposition and associated nutrient release from barrel medic (Medicago truncatula) hay and chickpea (Cicer arietinum) straw using an in vitro perfusion system

Two in vitro laboratory experiments were conducted to evaluate the effects of nutrient additions, soil inoculation, and sampling times on the decomposition rates and nutrient release patterns of leguminous crop residues. Cumulative CO2 evolution and the percentage nutrient release from barrel medic hay (Medicago truncat- ula) and chickpea straw (Cicer arietinum) were determined over a 6-week period using a 0.005 M CaCl2 recycling system (UNE in vitro perfusion apparatus). The decomposition study was carried out at 25°C in a controlled tem- perature laboratory. There were no significant differences between the decomposition rates of the 2 residues. The percentage C release was not significantly affected by nutrient addition or by soil inoculation. More than 50% of the total C that was released from the residues occurred in the first 7 days with peak release at 3-4 days. Because of an accumulation of nutrients in a muscilaginous substance in the apparatus, and adsorption of P to the plastic, it was not possible to measure the release of nutrients from the residues by sampling the perfusion solution. This had to be achieved by direct measurement of loss of nutrients from the residues. Except for K, the nutrient released from residues was not affected by residue or sampling time.

Method for rapid assessment of nutrient supply capacity of soils

Abstract A method to determine the nutrient supplying capacity of soils is presented which utilizes a nutrient solution in a lower container to supply designated nutrients to an upper container holding the soil. A series of nutrient solutions have been developed which maintain counter ion concentrations when a single nutrient is omitted from the solution. The validity of the technique is demonstrated by the agreement between plant yields, plant analysis data, and soil tests.