Grant W. Thomas

No-Tillage Agriculture

The no-tillage cropping system, a combination of ancient and modern agricultural practices, has been rapidly increasing in use. By the year 2000, as much as 65 percent of the acreage of crops grown in the United States may be grown by the no-tillage practice. Soil erosion, the major source of pollutants in rural streams, is virtually eliminated when no-tillage agriculture is practiced. The no-tillage system reduces the energy input into corn and soybean production by 7 and 18 percent, respectively, when compared to the conventional tillage system of moldboard plowing followed by disking. In addition, crop yields are as high as or higher than those obtained with traditional tillage practices on large areas of agricultural land.

Changes in soil properties after 10 years continuous non-tilled and conventionally tilled corn

Soil properties were evaluated after 10 years of continuous non-tilled and conventionally tilled corn (Zea mays L.) production on a Maury silt loam (Typic Paleudalfs) soil, which had been in bluegrass (Poa pratensis L.) for 50 years. On limed and nonlimed plots soil samples from 0, 84, 168 and 336 kg/ha N treatments were taken in the 0–5, 5–15 and 15–30 cm layers for determination of organic C and N, soil pH, and exchangeable Al, Mn, Ca, Mg, K. Tillage treatments had no effect on soil bulk density in the 0–15 cm layer. In the 0–5 cm surface layer, organic C and N were approximately twice as high with no-tillage as with conventional tillage; N fertilizer induced a high level of both organic C and organic N. No-tillage decreased soil pH for unlimed plots as compared to conventional tillage, especially at high N-rates, which produced an increase in exchangeable Al and Mn and a decrease in exchangeable Ca down to the 30 cm depth. When lime was applied, the pH of the surface soil was slightly higher under no-tillage. On treatments receiving lime, exchangeable Al and Mn levels were very low with no significant difference in tillage systems. At low rates of N fertilization the 10-year average corn yield was higher for conventional tillage than for no-tillage, but at high rates of N fertilization it was equal or higher for no-tillage treatments receiving lime. Unlimed no-tillage treatments produced lower yields at all N levels during 1975–1979. Deterioration of soil physical properties was not observed.

The effects of organic matter and tillage on maximum compactability of soils using the Proctor test

With the practice of continuous no-tillage, the question arises of whether, after a period of time, some sort of mechanical tillage will be required to alleviate compaction. Studies of maximum compaction using the Proctor test on a total of 36 samples from four Kentucky soils revealed that compactab

Changes in Soil Properties Under No-Tillage

When farmers shift from a system of agricultural production that includes numerous tillage operations to a reduced or no-tillage system it is reasonable to show concern about how this change in soil management may affect soil properties. For any crop production system to be widely accepted and used it must maintain the physical properties of the soil, and allow for replacement of nutrient removal and other losses. It must also maintain a soil environment favorable for the numerous necessary biological reactions. The microbial activity of the soil is largely determined by the chemical and physical properties of the soil. For example, the placement and amount of organic material directly influences biological activity, as it also does the chemical and physical properties.

Fertilization and Liming

Fertilizing and liming crops grown under no-tillage is not radically changed when compared to conventional practices. There are differences, however. Most of these differences arise from the fact that, under no tillage, the soil is not moved nor disturbed except in the slot where the seeds are placed. Also, under most systems of no-tillage, a residue of dead plant material is left on the soil surface and a kind of natural mulch is formed. The non-disturbance of soil resembles conditions in permanent pasture so that principles proved there are valid for row crops grown under no-tillage in general. The presence of a surface mulch changes the soil water regime, particularly at the soil surface. Principles of fertilization and liming for no-tillage are based on these two conditions as well as on the nutrient requirements of plants and the specific soil and climatic conditions encountered.

Phosphorus nutrition and water deficits in field-grown soybeans

Phosphorus and water deficits are important limiting factors in agricultural production. A field experiment was carried out with soybean (Glycine max (L.) Merr.) to determine whether the effect of water stress on field-grown soybean changes with soil P availability, and whether soil water content affects plant P nutrition. The soil was a Sadler series (fine-silty, mixed, mesic Glossic Fragiudalf) located at Princeton, Kentucky, USA (37°60′ north, 87°60′ west). The experiment was a factorial with three levels of soil P availability (4, 19 and 32 mg kg−1, Mehlich III) and two of water (irrigated and non-irrigated). Most of the effects of phosphorus and water stress on soybean growth were additive, so that, in general, effects of water stress were similar at each P level. Phosphorus deficiency slowed vegetative development, reduced shoot growth, LAI, P absorption and concentration, seed number, size and yield, and increased root length density in the surface soil. Water stress accelerated crop maturity, reduced shoot growth, LAI, P absorption and concentration, seed number, size and yield, and increased root length density. Some interactions between P and water were observed. Water stress slowed vegetative development only at the lowest P level (P0). The crop had a positive response to increasing P availability in both situations, with and without irrigation, suggesting that P addition would be justified even when a dry growing season is likely to occur.

Leaf area development in soybean as affected by phosphorus nutrition and water deficit

Leaf area development is an important factor in crop production because it affects the amount of radiation intercepted and, therefore, plant growth. Even though phosphorus (P) deficit and water stress have been studied as isolated factors limiting leaf area development in soybean (Glycine max (L.) Merr.), little has been done on their possible interactions. A pot experiment was conducted to determine the effects of P supply and water deficit on leaf-area development in soybean, and whether P nutrition affects soybean response to water stress. Plants were grown in pots for 49 days. The soil used was a Sadler silt loam (fine-silty, mixed, mesic Glossic Fragiudalf), which contained 5.3 mg P kg−1 (Mehlich III). Additional P was added at 0, 20, and 80 mg P kg−1 soil. Water treatments consisted of keeping the soil-water content at 85% (well watered), 60% (mild water stress) and 35% (severe water stress) of the 10 kPa soil-water content. Phosphorus nutrition did not affect the response of soybean to water stress in most of the measured variables. Relative reductions due to water stress were similar at every P level for individual leaf area, whole-plant leaf area, aboveground biomass, stomatal conductance, and transpiration. Only plant development was slowed to a greater extent by water stress in P-deficient plants. Water stress had no effect on P nutrition, since it did not affect P concentration in plant tissue.

Response ofPhaseolus vulgaris to inoculation withRhizobium phaseoli under two tillage systems in the dominican republic

SummaryField experiments were established at three locations in the Dominican Republic to evaluate the response of field beans (Phaseolus vulgaris L. cv. Pompadour) to inoculation with selected strains ofRhizobium phaseoli. A comparison of no-tillage and conventional tillage was included to determine whether modification of rhizosphere temperature and moisture would influence the inoculation response. Yields of inoculated treatments were not statistically difference from controls and ranged from 30–80% of those obtained on N-fertilized plots. Neither tillage systems nor P fertilization influence the response to inoculation. Serological investigations indicated that the applied rhizobial strains nodulated successfully. This host/endophyte combination appears to form an ineffective symbiotic association. Inoculation trials employing indigenous and commercial strains compared with N fertilizer in the greenhouse support the conclusion from the field studies that symbiotic N2 fixation can provide only a fraction of the plants N requirement.

Beyond exchangeable aluminum: Another ride on the merry‐go‐pound

Abstract At the time, rediscovery of exchangeable aluminum in the mid 1950s seemed to be a simplifying and unifying concept. That has not turned out to be the case. Rather, as more studies have been made we have come to know less what to expect in any given soil. Examples are polymer formation, interlaying of clay minerals with hydroxylated aluminum species and the reactions of aluminum with organic substances in soil. Viewed with the hindsight of 30 years, the exchangeable aluminum concept is still of great practical importance, but includes only one of the many fates of aluminum in soils. This paper discusses the findings made on aluminum since the 1950s and makes an attempt to rank their importance according to the opinion of the author.

Impact of Soil Management Practices on Nitrogen Leaching

ABSTRACT Soil management practices have an important influence upon N leaching. These practices include tillage, which may vary from region to region in the united States. The influence of tillage upon the soil water regime is discussed, including the effects upon evaporation from soil surfaces, paths of water flow, and pore size distribution. Nitrate leaching is considered as a function, first of soil water behavior and second of the abundance and distribution of nitrate in the soil. Amounts and forms of N in the soil are influenced by N transformations (nitrification, denitrification, and mineralization-immobilization). Soil management of water (including irrigation, drainage, and winter cropping) are also important in influencing nitrate leaching.