**3. Fundamental technique for assessing OPPS**

A technique used for assessing OPPS should be based on agroecosystem principles. In Ref. [10], there are 4 principle components of sustainable agroecosystem: productivity, stability, sustainability, and equitability.

The assessment of OPPS requires evaluation of aspects of plant productivity and S-L-E quality as well as changes in these aspects compared to their original use and/or previous conditions. Plant productivity is compiled from data and production potential. Soil quality score and land quality score could be determined in the representative area where the OPP are planted. Environmental quality is compiled in a similar way to the soil quality and land quality by selecting key environmental parameters. OPPS can be analyzed from changes or differences in the productivity value of plants, soil quality score, land quality score, and environmental quality score as compared to the original land use before planted by oil palm crop. All of these would be presented as the Plant Potential Productivity Index (PPPI), Soil Quality Index (SQI), Land Quality Index (LQI) and Environmental Quality Index (EQI).

In fact, not all OPP originate from forest clearing. Majority of OPPs do not come from forests, even from abandoned land ex-illegal logging, grasslands, shrubs, gardens that are not or less productive, etc. so that the effects of OPP on S-L-E quality and S-L-E degradation vary widely. The effect is strongly influenced by the origin or history before the OPP was created [11, 12], soil type, topography (especially slopes), climate (especially rainfall and climate type), applied management [13], both during land clearing and after planting, plant age, especially related plant factors and their influence on production, surface water absorption (infiltration), surface runoff and erosion and oil palm plantation management [14, 15]. It is necessary to study the effect of OPP on the degradation and improvement of S-L-E. The study especially needs to focus on the main issues that are accused of causing effects on S-L-E, including: 1) groundwater, 2) infiltration, 3) surface and river discharge, 4) soil erosion and sedimentation, 5) gas emissions and absorption greenhouse or carbon dioxide (CO2), 6) forest area, 7) biodiversity, and 8) degradation of peat lands.

All of sustainability evaluation of OPP effects would be presented as the PPPI, SQI, LQI and EQI. SQI and LQI could be developed to provide information about: 1) soil and land quality scores, 2) quality levels (very bad to very good), 3) growth inhibiting factors and crop production that needs to be addressed by soil-land management. If this information is correlated with production data, it can produce PPPI. SQI, LQI as well as EQI score is compiled by selecting key parameters, determining the weights and assigning a score to each parameter. Supported by PPPI together with SQI, LQI and EQI of all types of OPP with their area and their originate use area, an evaluation system could be developed which is very useful for S-L-E assessments to support OPPS in Indonesia.

The need and support to be able to evaluate empirically, measurably, objectively, quantitatively, accurately and periodically is increasing. Technological advances are

increasingly supporting the implementation of Agriculture 3.0 which is characterized by smart farming and precision farming and Agriculture 4.0 which is characterized by agricultural digitization. Support for quantitative land data is needed [16–18]. Software models are very helpful in simulating and predicting surface runoff, discharge, sediment loads, other environmental pollutants and helping to prepare recommendations for planning techniques for soil conservation and water improvement for SLE [19–23].
