Keith D. Wiebe

Land Tenure and the Adoption of Conservation Practices

We use a logit adoption model with data on 941 U.S. corn producers from the 1996 Agricultural Resource Management Study to analyze the influence of land tenure on the adoption of conservation practices. We extend previous analyses by distinguishing renters according to lease type and by distinguishing practices according to the timing of costs and returns. We find that cash-renters are less likely than owner-operators to use conservation tillage, but share-renters are not. Both cash-renters and share-renters are less likely than owner-operators to adopt practices that provide benefits only over the longer term (grassed waterways, stripcropping, and contour farming).

The Global Impact Of Soil Erosion On Productivity: I: Absolute and Relative Erosion-induced Yield Losses☆

Abstract Published studies relating erosion and productivity have been generally based on information derived from expert opinion on the extent and severity of soil erosion and on limited data on its impact on soil productivity, resulting in widely varying yield and economic loss estimates. In contrast, this report estimates the impact of soil erosion on productivity by collating, synthesizing and comparing the results from published site-specific soil erosion-productivity experiments at a global scale. Using crop yield as a proxy measure for soil productivity, this analysis uses the data from 179 plot-level studies from 37 countries identified in the soil science literature to calculate absolute and relative yield losses per Mg or cm of soil erosion for various crops, aggregated by continent and soil order. The results show that effects of past erosion on yields differ greatly by crop, continent and soil order. However, aggregated across soils on the continental level, absolute differences in productivity declines Mg −1 of soil erosion are fairly small. However, depending on the specific crop and soil, relative erosion-induced yield losses Mg −1 or cm −1 of soil erosion were two to six times smaller in North America and Europe than in Africa, Asia, Australia and Latin America. The higher losses in the latter continents are due primarily to much lower average yields, so that with identical amounts of erosion, yields decline more rapidly in relative terms. Studies using management practices as their experimental method to determine effects of present erosion showed much greater absolute and relative yield losses, which may be an artefact of the combined effect of erosion and variable management practices. Comparing the results of past and present erosion studies indicates that inappropriate soil management may amplify the effect of erosion on productivity by one or several orders of magnitude. Good soil management for effective erosion control and maintaining productivity, therefore, is imperative to meet the needs of the worlds present and future population.

Global Soil Nutrient Depletion and Yield Reduction

ABSTRACT Nutrient depletion in soils adversely affects soil quality and reduces crop yield and consequently poses a potential threat to global food security and agricultural sustainability. With an emphasis on human-induced nutrient depletion, this paper described the causality among soil nutrient depletion, soil quality, crop production, socio-economic variables, and environmental condition. Then, global soil nutrient budgets of nitrogen (N), phosphorus (P), and potassium (K) were estimated for wheat (Triticum aestivum L.), rice (Oryza sativa), maize (Zea mays L.), and barley (Hordeum vulgare) production for the year 2000. As a result, there were unbalanced fertilization with surplus N in some developing countries and insufficient inputs in many developing and all least developed countries. Globally, soil nutrient deficits were estimated at an average rate (kg ha−1 yr−1) of 18.7 N, 5.1 P, and 38.8 K, covering 59%, 85%, and 90% of harvested area in the year 2000, respectively, and annual total nutrient deficit was 5.5 Tg (1 Tg = 1012 g) N, 2.3 Tg P, and 12.2 Tg K, coupled with a total potential global production loss of 1,136 Tg yr−1. Besides socio-economic factors, the soil nutrient depletion can be attributed to insufficient fertilizer use, unbalanced fertilization, and nutrient depletion-induced soil fertility problems. Soil fertility problems associated with human-induced nutrient depletion are widespread worldwide.

Impact of soil erosion on crop yields in North America

Publisher Summary This chapter uses spatially referenced data to link study sites with soil orders and erosion rates to estimate the productivity losses in each soil order. This information is used to estimate the production and economic losses due to soil erosion for four crops that have been the subject of most erosion-productivity studies in North America: maize ( Zea mays L.), wheat ( Triticum aestivum L.), soybeans ( Glycine max (L.) Merr.), and cotton ( Gossypium spp. L.). Soil loss is used as an indicator of erosion. In accord with most of the studies reviewed, topsoil depth (TSD) is used as the independent variable. Furthermore, several features of the estimated aggregate annual economic losses in productivity due to soil erosion are important. Each of these features underscores the success of past policy measures in providing farmers with incentives to adopt soil conservation measures, and the importance of continued policy efforts to promote such adoption in the future, to realize conservation goals that are important to society as a whole and to sustain productivity levels over the long term.

Crop Response in Salt-Affected Soils

ABSTRACT Salt-affected soils, those on which plant growth is limited by an excess of salts, are of three types: (i) saline soils in which electrical conductivity is > 4 dSm−1; (ii) sodic soils in which the exchangeable sodium percentage (ESP) is > 15; and (iii) saline-sodic in which the electrical conductivity (EC) is > 4 dSm−1 and ESP is > 15. Salt-affected soils are most common in aridic moisture regimes, and secondary salinization (due to anthropogenic activities such as irrigation) may occur by improper management of irrigation. Estimates of the area of salt-affected soils vary widely, ranging from 6% to 10% of earths land area, and 77 million hectares (Mha) of irrigated lands. Crop yields are drastically affected due to lack of availability of water, nutrients, and oxygen in the root zone. The magnitude of yield reduction depends on the crop, soil type, and management. The reduction in yield normally ranges from 10% to 90% for wheat, 30% to 50% for rice, 50% to 75% for cotton, and 30% to 90% for sugarcane. Crop yield can be enhanced by nutrient management (especially N), water management (irrigation with good quality water and appropriate drainage), use of soil amendments (manures and gypsum, etc.), and use of salt-tolerant varieties.