by Raymond P. Poincelot
page 1-2
by Raymond P. Poincelot
page 3-4
by Maurice A. Okoji and Julia Moses
page 5-13
By its location on a lowland coastal plain, Akwa Ibom State should not be menaced by soil degradation through erosion. But some of its component areas are characterised with hill ranges which are intensively cultivated. With a high mean annual rainfall of 4020 mm and its attendant impact on the generally sandy loam soils, these areas have become victims of environmental degradation and require soil conservation. The age old techniques of soil conservation such as earth works and mechanically constructed waterways are known to be of high initial outlay with little or no return to investment capital through crop yield. On the contrary, agroforestry is looked upon as inexpensive but with the potential to achieve more than mechanical structures in erosion control, maintenance of soil organic matter and physical properties as well as in the promotion of efficient nutrient cycling and high yield. It is also seen as an important farming package for sloping lands and an easily adoptable innovation in soil conservation. A change in soil conservation policy is recommended.
by R. Lal and B. R. Singh
page 15-36
A rapid increase in population is causing severe strain on natural resources and environment of East Africa. Per capita arable land area is declined in several densely populated regions of East Africa. Two major issues in soil and environment degradation, i.e., greenhouse effect and water quality are described. Three principal soil degradation processes with reference to productivity are physical, chemical and biological degradation. Soil physical degradation can affect crop growth and yield by decreasing root depth and available water and nutrient reserves and soil erosion can lead to yield loss by affecting soil organic carbon, nitrogen, phosphorus, and potassium contents and soil pH. Reduction in maize grain yield on moderately and severely eroded soils compared with uneroded soils in Tanzania was 14 to 39%. Chemical degradation is caused by the processes of nutrient depletion and/or loss of organic matter, acidification and toxic aluminum, salinization, and industrial and mining activities. In #Tanzania, a modest cropping system of maize and bean removed about 58, 13, and 56 kg ha-1 of N, P, and K, respectively. The average use of fertilizers in this cropping system was only 22.5 kg ha-1 and thus resulting in "nutrient mining." Principal issues of agricultural sustainability are discussed.
by K. Bradley Watkins and Yao-Chi Lu
page 37-53
this study measures the economic and environmental outcomes associated with using two-, three- and four-year seed potato rotations in Southeastern Idaho. Seed potatoes are rotated with spring wheat, feed barley, oats, and canola. Crop yields, nitrogen loss, and soil erosion are simulated using the EPIC biological simulation model. A tradeoff frontier approach is used to screen out inferior rotations and to calculate tradeoffs between economic returns, reduced nitrogen loss, and reduced soil erosion. The results reveal that the most profitable and environmentally sound rotations tend to be three-year rotations of potatoes followed by two grain crops, with spring wheat occurring at least once in the crop sequence. A two-year potato-wheat rotation resulted in the largest economic return, a three-year potato-wheat-wheat rotation resulted in the second largest return and the smallest soil erosion, and a four-year potato-barley-wheat-wheat rotation resulted in the smallest nitrogen loss.
by Mark W. Schonbeck and Gregory K. Evanylo
page 55-81
The effects of hay, compost, plastic and paper mulches on soil temperature, soil moisture and yield of paste tomato were evaluated on five farms in Virginia. Organic mulches reduced afternoon soil temperature and maintained higher soil moisture levels than other treatments. Black plastic mulch increased soil temperatures by 1-2 degrees C, but sometimes resulted in lower soil moisture levels in early summer, probably by hindering penetration of rainfall. Both undyed kraft paper and black paper mulches reduced afternoon soil temperatures slightly. Oiled paper initially increased afternoon soil temperature by 4 degrees C, but this effect diminished over time. Paper mulches decomposed before the end of the season, allowing increased evaporative losses of soil moisture.
Mulch treatments apparently affected early tomato yield by influencing soil temperature regime, but affected later yields by modifying soil moisture levels. Early yields were generally highest with black plastic mulch and lowest in organic mulches, with paper mulch intermediate. At sites not affected by late blight, total yields were generally: organic mulch >/= plastic >/= paper > unmulched. At sites affected by late blight, later-maturing fruit were lost, so that the delay in ripening in soil-cooling organic mulches resulted in a significant yield reduction compared to black plastic.
by Mark W. Schonbeck and Gregory K. Evanylo
page 83-100
Potential contributions several mulches to soil organic matter (OM), and their effects on crop-available nitrogen (N), earthworm activity and tilth-related soil properties, were evaluated on five working vegetable farms in Virginia. A 100-mm thick hay mulch added sufficient organic carbon (C ) and N to replace seasonal soil OM losses expected for temperate zone soils. Paper and plastic mulches contributed little or not OM, but mulching alleys between film-mulched beds helped replenish soil OM in these mulching systems.
Transcribed by Emma McCulloch
21 January 1999