Autoguidance system operated at high speed causes almost no tomato damage

Soil Conditioners

Soil conditioners usually are defined by soil scientists as materials which when applied to the soil can serve to improve a soil’s physical condition. In general, this refers to an improvement in the development of soil structure which will result in improved aeration and water relationships. Certainly, maintaining and/or improving soil structure is highly desirable in soils utilized for crop production. Addition of organic matter to the soil is the most common method for improving soil structure. Traditional additives include crop residues, livestock manures and sewage sludge. Non-traditional soil conditioners include both organic and inorganic products. The most common types of non-traditional materials include the following:

1) Composted organic materials which also may be supplemented with organic materials, such as unprocessed rock phosphate or ground limestone. The composition of these materials may be quite variable depending upon what has been added. In addition, these materials also may be extracts of livestock manure or other organic residues which are marketed as liquids.

2) Mined mineral deposits which are marketed unprocessed except for grinding. Again, the composition of these materials can be highly variable, but may include granite, glauconite (a mineral high in unavailable potassium), and natural deposits containing primarily gypsum or sand.

3) Mined humates or humic acids. These materials are prehistoric organic deposits which are in the advanced stages of transformation into coal and are normally discarded during mining. Liquid humates also have been marketed and are, presumably, a concentrate of humic acids.

4) Various inorganic solids such as evaporated sea water or sulfates which may be combined with organic extracts of materials like kelp (sea weed) or whey.

Humates and/ or humic acid represent good examples of non-traditional soil conditioners. A number of research trials have been conducted across the United States to evaluate the effects of humates on soil properties and crop growth. Studies conducted in Kansas (Table 1) showed that humate did not significantly improve corn grain yields over a three year-study period. Similar results have been observed using a related material called leonardite, and organic, coal-like deposit, which also reportedly is high in humic acid. Research in Illinois, North Dakota and Canada showed no significant improvement in yields of corn grain, corn silage, wheat, barley and field beans due to soil conditioner treatments when various products were applied alone or in combination with commercial fertilizer. in contrast, yields in most studies were consistently improved by addition of irrigation water and traditional commercial fertilizer treatments.

Soil Activators

Soil activators are commonly marketed on the basis that they stimulate existing soil microbes or inoculate the soil with new beneficial organisms. In some cases, manufacturers suggest that products may improve soil physical properties (increase structure, reduce compaction), increase fertilizer and soil nutrient uptake, improve crop yields and/ or quality, correct soil “toxicities” (such as salinity) and provide disease and insect resistance. Most soil microbiologists agree that to significantly increase the activity of soil microbes for more than a few hours, a minimum of several hundred pounds of organic material must be added to the soil. However, these products often are applied at rates of only a few pounds per acre. At these rates, only relatively small numbers of microbes are being added to the soil compared to the existing numbers of bacteria, fungi, and actinomycetes, which may number from 1 million to 1 billion cells per gram of soil. In other words, we may be adding 1 pound per acre or less of microbes to a soil which already contains 2000 to 4000 pounds of microbes per acre.

Numerous research studies have been conducted across the United States over the years to investigate the potential beneficial effects of various soil activators. In general, these studies have shown no significant beneficial effects of these products on crop yields or quality. Table 2 shows the results of field studies conducted in Texas using two soil activator products. In both fertilized and unfertilized plots, neither product increased yields of grain sorghum or cotton above the check plot. Laboratory evaluations of these products also indicated that they did not increase the numbers of activity of soil microbes and thus, would not be expected to increase the rate or extent of crop residue decomposition.

Other field trials using these products were conducted on forages, peanuts, rice, soybeans and tomatoes by researchers in Texas, Alabama, Louisiana and Oklahoma. These studies consistently indicated that neither product had a significant effect on yields of the various crops under the different soil and climatic conditions. This work is extremely important, particularly because it included 22 different soil series ranging from fine sands to clays (pH range from 4.8 to 8.4) and because the work was continued at the same locations over a 2- to 3- year period to verify results.

Certainly, inoculation to stimulate the development of certain types of beneficial microorganisms is not uncommon. In certain sewage treatment processes and composting operations, a portion of the treated material may be used to provide “seed” organisms to the unprocessed material. An example in agriculture is inoculation of seed with Rhizobium bacteria to promote good nodulation in legume crops. However, these biological processes have been thoroughly investigated and the potential benefits reasonably well documented.

Table 1. Effects of humate on yields of irrigated corn.1

Treatment	Grain Yield (bu/acre)
Treatment	1978	1979	1980	Average
Control (no fertilizer)	211	152	170	178
50 lbs. 18-46-0/ acre	213	149	177	180
50 lbs. 18-46-0/ acre + 250 lbs. Humate/ acre	208	162	172	181
50 lbs. 18-46-0/ acre + 500 lbs. Humate/ acre	210	162	172	181
¹Adapted from Lawless et al., 1984

Table 2. Grain sorghum and cotton yields at three locations as affected by application of two soil additives and fertilizer1

Fertility Treatment	Sorghum GrainYield (lb/acre)			Cotton Lint Yield (lb/acre)
Fertility Treatment	Beeville	McGregor	Temple	McGregor	El Paso	Lubbock
Unfertilized Check Product A Product B Fertilized Check Product A Product B	175 140 217 1110 900 1041	2057 1854 2036 2543 2514 2365	2218 2233 2202 2237 2352 2352	194 199 193 265 240 240	806 842 777 743 766 749	290 301 310 393 370 397
¹Adapted from Weaver et al., 1974