For thousands of years, agriculture and tillage were considered synonymous. It was simply not thought possible to grow crops without first tilling the soil before planting and for weed control. The advent of modern herbicides permitted no‐tillage (NT) to be developed and practiced on actual working family farms. No‐tillage is generally defined as planting crops in unprepared soil with at least 30% mulch cover. Adoption of NT after its successful demonstration in the 1950s was slow. However, with better planters, herbicides, and accumulated experience, NT began to be widely adopted in the 1980s in the United States and then in Australia, South America, and Canada. Today, approximately 23% of the total cropland in the United States is planted using NT. No‐tillage has revolutionized agricultural systems because it allows individual producers to manage greater amounts of land with reduced energy, labor, and machinery inputs. At the same time, NT is a very effective erosion control measure and improves water and fertilizer use efficiency so that many crops yield better under NT than under tilled systems. Tillage, like crops, can be rotated but the benefits of NT are most likely to be realized with continuous application. We review some of the early work that led to the development of NT and how NT impacts the crop, soil, hydrology, and farm economics. While highly sustainable, there are still many challenges that remain for researchers to solve so the benefits of NT can be realized on expanded land area and for more crops, worldwide.

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A simple and precise colorimetric method of determining orthophosphate in aqueous solutions containing labile organic and inorganic P compounds is described. It involves a rapid formation of molybdenum blue color by the reaction of orthophosphate with molybdate ions in the presence of ascorbic acid‐trichloroacetic acid and citrate‐arsenite reagents and complexation of the excess molybdate ions to prevent further formation of blue color from the phosphate derived from hydrolysis of the acid‐labile P compounds. The color is stable up to 24 hours. The method is sensitive and accurate, and it permits determination of microgram quantities of orthophosphate in samples containing large amounts of acid‐labile P compounds.Tests with a wide range of condensed phosphate and organic phosphate compounds showed that none of the P compounds studied interfered with this method. Results by this method are compared with those obtained by the method of Murphy and Riley.

No‐tillage (NT), minimum tillage (MT), and conventional tillage (CT) practices were continuously applied to a Hoytville silty clay loam (Mollic Ochraqualf) soil (18 years) and a Wooster silt loam (Typic Fragiudalf) soil (19 years) in Ohio. The effect of the various tillage intensities on the profile (0–30 cm) distribution of organic C, N, and P concentrations and pH was investigated. Results showed that NT resulted in significantly (P < 0.05) higher organic C and N concentrations in the 0‐ to 15‐cm soil increment of the Hoytville soil but significantly lower concentrations in the 15‐ to 30‐cm soil increment. For the Wooster soil, NT resulted in higher concentrations in the 0‐ to 7.5‐cm soil increment. No significant differences were observed among tillage intensities in the 7.5‐ to 30‐cm soil increment. Comparison of organic C concentrations in the plow layer (0–22.5 cm) of the soils at the beginning of the long‐term tillage experiment and at present showed that concentrations remained constant or decreased 11% under NT in the Hoytville and Wooster soils, respectively. Present organic C concentrations in the Hoytville soil were decreased 12 to 14% by long term MT or CT while a 23 to 25% decrease was observed for the Wooster soil. Organic P concentrations under NT were significantly (P < 0.05) higher in the 0‐ to 7.5‐cm increment of the Wooster soil and significantly lower in the 22.5‐ to 30‐cm soil increment. Organic C/N, C/P, and N/P ratios were calculated and higher ratios were observed under NT than under MT or CT in the surface soil increments. Tillage intensity, however, had little effect on the ratios averaged over the entire profile (0–30 cm). Soil pH was 0.1 to 0.3 units lower (P < 0.05) under NT in all soil increments except in the 22.5‐ to 30‐cm increment of the Wooster soil where no significant differences in pH were observed among the tillage intensities.

Soil enzyme activities are often used as indices of microbial growth and activity in soils. Quantitative information concerning which soil enzymes most accurately reflect microbial growth and activity is lacking. Relationships between the activities of 11 soil enzymes and microbial respiration, biomass, viable plate counts, and soil properties were determined in surface samples of 10 diverse soils. Correlation analyses showed that alkaline phosphatase, amidase, α‐glucosidase, and dehydrogenase activities were significantly (P < 0.01) related to microbial respiration as measured by CO2 evolution in soils which had received glucose amendments. Phosphodiesterase, arylsulfatase, invertase, α‐galactosidase, and catalase activities were correlated at the 5% level while acid phosphatase and urease activities were not significantly correlated to microbial respiration. There was no significant correlation between the 11 soil enzymes assayed and CO2 evolution in the 10 unamended soils. Only phosphodiesterase and α‐galactosidase activities were significantly (P < 0.05) related to microbial numbers obtained on some selective culture media. Alkaline phosphatase, amidase, and catalase were highly correlated (P < 0.01) with microbial biomass as determined by CO2 evolution after chloroform fumigation pretreatment. The organic C content in the 10 surface soils was correlated (P < 0.05) with acid and alkaline phosphatase, phosphodiesterase, arylsulfatase, amidase, urease, and invertase activities. Urease activity was also positively correlated with total N and cation exchange capacity and negatively correlated with the percentage of sand. These relationships suggest that urease can exist in soil as an extracellular enzyme in a three‐dimensional network of organo‐mineral complexes. Of the 11 enzymes evaluated, alkaline phosphatase, amidase, and catalase were concluded to be the most satisfactory choices in determining the relative activity and mass of the microbial population in soils. The activities of these enzymes were highly correlated with both microbial respiration and total biomass in soils.

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