Global interactive index for soil production and degradation assessment

Nowadays there is a common concern: how to evaluate the productive capacity and productive risk of different soils and how to estimate the productive loss due to soil degradation. In this work a new index and the use of crop models of simulation is proposed.

With the goal of reaching systems of sustainable agriculture, the use of adequate indicators are indicated to detect if certain management practices in agriculture favor soil degradation or contribute to revert that process. Many researchers use to monitor relevant soil attributes, which depends on the soil and management system. These attributes constitute a minimum dates set (MDS) that allows detecting several degradation levels. However, even when MDS are available, they only have information of isolated dynamics of some soil properties. Although that method is good to control the soil degradation evolution, it doesn't provide quantitative information about the productivity of the soil taking into account the interactions soil-climate-crop-technology. This kind o information can be generated inserting the attributes in simulation models of crop growth.

This work intends to use the models to establish global and interactive indexes: global because they include all variables of interest: soil properties, environmental variables, crop characteristics, and management indicators that influence the production; interactive because when an input variable is modified in the model, the rest automatically is also altered. Two indexes that express the yield and risk of production are proposed to better evaluate the soils: the poprodin and the degradin.

Poprodin (potential production index): it indicates how much a soil can produce regarding to the potential given by the climate and crop.

Degradin (degradation index): it evaluates how much a soil has been deteriorated (or not) regarding to the same soil in its natural condition.

These index can be calculated as shown:

Poprodin = Production of the natural soil / Potential Production

Degradin = 100 * (Production of the natural soil – Production of the cultivated soil) / Production of the natural soil

To calculate these indexes are used results of simulation models of crop growth, standing out the possibility of quantifying the potential yield and the evaluation of the productive risk, two estimates difficult to achieve for other means.

The FitoSim model was used in this work. This model is based on general laws of crop growth under ideal conditions as well as under conditions of water and mineral stress. It calculates the maximum growth and production that it is possible to wait according to each particular interaction genotype-environment; it also simulates the radical activity in stratified soils and that have varied limitations. This way, the model allows considering the effect of different management systems.

The growth of three crops was simulated (wheat, corn and soy-bean) in four soils of diverse productive capacity. Fifty years of meteorological data, representative of the climate of the center of Santa Fe (Argentina) were also used to run the model. Sow date for summer crops: November 15; sow date for winter crop: July 15. The soils were: Typic Argiudol, Esperanza Series (capability use I₂, index of productivity (IP): 81); Aquic Argiudol, Recreo Series (IIw, IP: 56); Typic Natralbo, Cululú Series (IVws, IP: 28), and Typic Natracualf, Río Salad Series (VIws, IP: 13). All soils were evaluated under natural conditions (N), and after being used for continuous conventional agriculture for more than 30 years. Diverse erosion levels were also simulated. The potential yield, for each interaction climate-crop without soil limitations, was estimated. The results are shown in the Table.

Poprodin decrease with the decrease of the soil productivity index, indicating the suitability of the poprodin to quantify the differences in the productive capacity of the studied soils. The considered crops show different production capacities in different soils.

Degradin points out the soil deterioration degree induced by a non conservationist use. Several soil erosion levels induce a decrease in the soil productive capability, which is indicated by the differences in the degrading, as shown in the following table.

The better condition (natural soil without erosion) is identified with a degradin value=0. On the other hand, the worse soil condition (degradin=69) explains the loss of productivity caused by the improper soil management.

The proposed indexes can improve others that only are based on the static evaluation of some attributes because they combine all involved factors and their interactions. The index can be transformed in monetary values, which make possible to evaluate soils of different quality. Moreover, the costs of the soil degradation and recovering practices can be assessed, which allow people to tax them in business.