2. You have planted corn on two fields. Both fields are on the same soil series,

Question

2. You have planted corn on two fields. Both fields are on the same soil series, both have the same amount of fertilizer added. One soil has 4% SOM (soil organic matter) and one has 0.5% SOM. Could this difference impact the yield? How? B. How is this related to net primary productivity (NPP)? 2. You have planted corn on two fields. Both fields are on the same soil series, both have the same amount of fertilizer added. One soil has 4% SOM (soil organic matter) and one has 0.5% SOM. Could this difference impact the yield? How? B. How is this related to net primary productivity (NPP)? 2. You have planted corn on two fields. Both fields are on the same soil series, both have the same amount of fertilizer added. One soil has 4% SOM (soil organic matter) and one has 0.5% SOM. Could this difference impact the yield? How? B. How is this related to net primary productivity (NPP)?

Explanation / Answer

2 (A) Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesized by soil organisms. Plant productivity is linked closely to organic matter. Consequently, landscapes with variable organic matter usually show variations in productivity. Plants growing in well-aerated soils are less stressed by drought or excess water. In soils with less compaction, plant roots can penetrate and flourish more readily. High organic matter increases productivity and, in turn, high productivity increases organic matter. The climatic constraints are taken care by adding fertilizers. The application of inorganic fertilizers on depleted soils often fails to provide the expected benefits. This is basically because of low organic matter and low biological activity in the soil. The chemical and nutritional benefits of organic matter are related to the cycling of plant nutrients and the ability of the soil to supply nutrients for plant growth. Organic matter retains plant nutrients and prevents them leaching to deeper soil layers. Microorganisms are responsible for the mineralization and immobilization of N, P and S through the decomposition of organic matter. Thus, they contribute to the gradual and continuous liberation of plant nutrients. Available nutrients that are not taken up by the plants are retained by soil organisms. In organic-matter depleted soils, these nutrients would be lost from the system through leaching and runoff. Usually agronomy practices that influence nutrient cycling, especially mineralization and immobilization, result in an immediate productivity gain or loss, which is reflected in the economics of the agricultural system. Crop yields in systems with high soil organic matter content are less variable than those in soil that are low in organic matter. This is because of the stabilizing effects of favorable conditions of soil properties and microclimate. Improvements in crop growth and vigor stem from direct and indirect effects. Therefore the soil with 4 % soil organic matter would yield a higher amount of crop as compared to the soil having 0.5 % soil organic matter.

(B) Net Primary Productivity (NPP) is defined as the net flux of carbon from the atmosphere into green plants per unit time. NPP refers to a rate process, i.e., the amount of vegetable matter produced (net primary production) per day, week, or year. The CO2 uptake through photosynthesis and plant growth, and loss of CO2 through respiration and decomposition of organic matter from terrestrial ecosystems are significant fluxes play an important part in carbon dynamics and vegetation modelling. 95% of plants produce three-carbon organic acids in carbon fixation. 3% produce four-carbon organic acids and more sugar. The composition of litter and residues, however, requires the calculation of carbon allocation between different plant organs (leaves, stems, roots), which can be estimated from total carbon uptake using fractional parameters. The newly allocated carbon to plant organs will be accumulated or enter the soil as vegetation litter. The equilibrium state is reached when carbon gain through the allocation equals carbon loss through litter production. However a balance is achieved between the carbon taken up in photosynthesis and the carbon released back to the atmosphere from respiration, oxidation of dead organic matter. Therefore the NPP will be higher if soil organic matter content is higher as they both are directly proportional to each other.

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