Few plant breeding programs involve attempts to develop varieties specifically adapted to low-input cropping systems. Plant breeders generally select varieties in highly fertile, weed-free, densely seeded environments. However, alleles needed for achieving maximum yield in low-input environments often differ from those required in highinput conditions. Thus, when effective selection can be undertaken under low-input conditions, breeding programs specifically targeted at low-input environments should produce the best varieties for those environments. Experimental protocols for identifying such situations are described in this review. These involve (a) testing breeding lines under low- and high-input conditions, (b) estimating both the degree to which yields from the two types of environment are controlled by the same alleles and the relative accuracy with which superior genotypes can be identified in low- and high-input environments, and (c) predicting the direct and indirect responses to selection at each input level. On the basis of published data, it seems feasible to develop corn hybrids specifically adapted to production with lower rates of N application than are now commonly used in the United States.

On-farm field demonstrations provide a useful method of technology transfer for researchers and extension specialists, and the proponents of alternative agriculture have adopted on-farm experimentation as an important means to establish the value of sustainable methods. For on-farm research long narrow strips harvested by machine are often employed in place of small hand-harvested plots commonly used at research facilities. The use of this approach, however, could bring the methodology into question if field variation should make determination of statistical differences difficult. Analysis of harvest data from ten irrigated and four dryland site-years for small hand-harvested corn plots and for machine-harvested long narrow strips was conducted to determine the impact of sampling method upon experimental variation. Analyses of variance indicated that six of the ten machine-harvested irrigated sites had significant yield response to applied nitrogen while only one of the ten hand-harvested sites exhibited significant nitrogen effects (P ≤ 0.10). The difference in statistical precision was not a result of increased range in yields, but rather of more consistent yields for each treatment. An economic analysis was performed, and the results indicated that optimum nitrogen rates depended on corn and nitrogen price ratios. When 1989 corn and nitrogen prices were used, the calculated marginal profit levels between the reduced nitrogen and recommended nitrogen rate ranged from $8.92 to -$8.14 per ha. For the irrigated sites, when experimental variation (F-test of total sum of squares) was compared by harvest method, hand harvest had significantly greater variation than machine harvest in five experiments. Machine harvest was significantly more variable in one comparison. Coefficients of variation for machine harvest were less than for hand harvest in nine of ten irrigated experiments. For the dryland sites, differences between harvest methods were significant in one of four experiments. These data suggest that under certain conditions machine-harvested long narrow strips provide more accurate estimates of treatment differences than do small hand-harvested plots despite potential differences in soil texture, soil fertility, or available soil water.

Winter legume cover crops are receiving increasing attention from agronomists and farmers as a source of nitrogen for summer crops. While agronomists are continually providing new technical information on using legumes as a nitrogen source, little is known on the economics of their use. Previous economic research on legume cover crops has focused mainly on budgeting analysis. In the present work, a twofactorial experiment was designed to test the use of legumes as a nitrogen source for corn (Zea mays L.) in north Georgia. The first factor was winter cover crop with treatments being crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth), wheat (Triticum aestivum L.), and no cover crop or winter fallow. The second factor was nitrogen (N) fertilizer applied at five different rates: 0, 25, 50, 100, or 200 pounds per acre. For each combination of the two factors, mean yield and yield variance were determined. Results indicated that legume cover crops increased both average corn yield and yield variance. The greater yield variance from the use of legume cover crops increases economic risk. Risk-averse farmers must be compensated for increased profit variance by higher average profits. A safety first method was used to evaluate the tradeoff between average profit and profit variance for the risk-averse individual The results showed that hairy vetch with 50 pounds of N per acre was the best combination of cover crop and fertilizer rate for risk-neutral farmers. For risk-averse farmers, hairy vetch without any nitrogen fertilizer is preferred.

Conventional, low-yield aquaculture methods use earthen, standing water fish ponds that typically are stocked with 0.5 to 2 fish/m2 and produce 3 to 10 tons of fish/ha/year using refined feeds. At higher fish stocking densities and fish yield, production of metabolites and residues exceeds such a pond's natural recycling capability, so that a higher rate of flushing is required. This wastes water and valuable nutrients and creates a potentially polluting effluent In an alternative system, by increasing the rate at which the metabolites and feed wastes are microbially processed within the culture system, production rates exceeding 500 tons of tilapia fish/ha/year have been attained with less than 0.5 percent water change daily. In preliminary experiments in this closed bioconversion system, we have replaced all formulated feeds with agricultural residues and fertilizers, which are converted into protein by intense microbial processing. The rate of fish growth indicated that much or possibly all the feed requirements of tilapia grown in this type of closed, densely stocked system can be satisfied by intense cultivation of heterotrophic microbes.

I reexamined five previously published studies that compared the economics of high input conventional crop production systems in various regions to the economics of lower input alternatives that use green manures, cover crops, and more diversified rotations, but no inorganic fertilizers and little or no synthetic pesticides. The original analyses were extended to include estimates of each production system's contribution to the local economy, both directly through farmers' payments for labor and interest, and indirectly through the payrolls and profits of enterprises serving farmers. A similar comparison was also made for high input irrigated and lower input nonirrigated corn production. On a per acre basis, the high input systems' local economic benefits were equal to or greater than those of the lower input systems. However, they were lower as a fraction of total value of production in all but one case, since production was always higher for the higher input systems. Correspondingly, with all but one of the higher input systems, a greater portion of the value of production left the local economy to pay for purchased inputs. This becomes significant if the production system is not sustainable, so that the total productive potential of the area's agricultural resources is finite when integrated over their entire economic life. In such circumstances, the results imply that under the conventional system the local economy will capture a smaller share of the total productive value of those resources.

In the region concerned, agriculture is conducted under stress from several difficult circumstances. These difficulties include, among others, drought, a limited length of growing season, harsh winters, insect pests and diseases, and weeds. The present paper describes several measures that are taken to combat these problems. Control devices include legume green manure/cereal rotations, use of drought-resistant and insect-resistant varieties, and early seeding of spring grain to cause maturation before the period of maximum drought risk. Recently, a wide range of legumes has been grown on a limited basis in the region, and further progress toward improved legume varieties is being pursued.