Reniform (Rotylenchulus reniformis) and root-knot (Meloidogyne incognita) nematodes have become an increasingly important problem in cotton production in the United States and Florida. Management of nematodes is accomplished by crop rotation, nematicides, or a combination of these practices since complete resistance of cotton cultivars is not available. However, there are some varieties on the market that have some level of resistance to root knot nematode. For many growers, rotation is not seen as an option because of low alternative commodity prices, and the most effective nematicides are very costly or have been taken off the market. Thus, practices need to be developed to provide more flexibility to manage nematodes. Our research using strip-till planting has centered on cultural practices that could potentially reduce cotton losses from nematodes at little cost to growers. These have included planting cotton between previous crop rows, increasing cotton plant populations, and destroying cotton roots soon after harvest. In a preliminary trial, cotton planted strip-till between previous cotton rows showed positive results. Cotton lint yield was increased 29% by planting between previous rows as compared to planting into the old cotton row. Further tests, as described here, have confirmed the usefulness of planting between previous cotton rows to reduce losses from reniform nematodes. Precision farming techniques allow farmers to plant back over the row from the previous year to take advantage of the subsoil slot or starter fertilizer that was applied near the row. However, this may result in a yield reduction. There is a consistent yield reduction for each year in cotton without rotation. The perennial nature of cotton allows roots to continue growing late into the fall until a killing frost occurs. In some years the root system is never killed and nematodes that have colonized on the roots can quickly migrate to the new crop the next year when planted over the same row.
Two field trials, one each year, were conducted at the North Florida Research and Education Center near Quincy, Florida, on a loamy sand soil (80% sand, 8% silt, 12% clay) infested with reniform nematodes. Cotton was grown on this site the year before, and the mowed stubble was left undisturbed over the winter. Two cotton cultivars were planted using strip tillage in June of each year. Rows were 36 inches wide, and the two treatments consisted of planting cotton directly in-row over the old cotton stubble or planting between the previous cotton rows. The treatments were alternated and replicated six times. Cotton was maintained using standard cultural practices for Florida. Soil samples for nematode analysis and plant yield were collected from two rows per plot. When soil samples were taken concurrently in the cotton row and between rows, individual cores were taken across from each other to insure comparable sampling areas. Soil was collected for reniform nematode extraction and counted using standard techniques. Cotton was harvested with a spindle picker in early December in the two tests, and subsamples were ginned for lint yield.
In Test 1, reniform nematode population densities 28 days after planting were lower in cotton planted between previous rows than where planted over the previous rows (Table 1). As the season progressed, reniform nematode population densities in-row in both treatments increased and were roughly equal 76 days after planting. Samples taken after 136 days were collected both in-row and between rows of the two treatments. Reniform nematode population densities were significantly higher in-row in both treatments (mean-1603/100 cm3 soil) compared to row middle populations (mean-544/100 cm3 soil). Cotton yield mirrored early season nematode population density. Yield was significantly higher in cotton planted between previous cotton rows compared to in-row planting.
In Year 2, initial reniform nematode population densities were lower between previous cotton rows than those taken in the old cotton row (Table 2). At both the 81 and 153 day sampling dates, reniform population densities did not differ between the two treatments (Table 3). Additionally, nematode population densities between row middles of both previous-year treatments did not differ from each other but were significantly lower than those found in the planted row of either treatment. Due to the initially lower populations of reniform nematodes in row middles, however, cotton lint yield was significantly higher than in-row plantings (Table 2).
Present information supports the idea that planting cotton in previous row middles when strip-till planting will help avoid a portion of potential yield losses due to reniform or other nematodes. This is due to population densities of reniform nematodes that are lower between rows as compared to in-row populations. However, plant growth, hence root spread, is probably an important factor in the success of this technique. Auto-steer and other current technology make it easy for growers to plant between previous cotton rows or directly back over the old row. As nematode population is determined throughout the field by direct sampling or by electrical conductivity, variable-rate nematicide application is feasible and is becoming more commonplace as knowledge about fields is obtained. However, we do know that row-middle plantings could increase nematicide performance. Also, shifting to row-middle plantings using strip-till technology does not involve additional grower expense, so any yield improvement would be profitable for the cotton farmer.
Concern about compaction has often been the motivating factor in planting back over the old row instead of in previous row middles. This research indicates that where reniform nematodes (and probably root-knot nematodes) are a problem, it pays to strip-till in row middles. Compaction in row middles should not be a problem with the use of chisels or subsoilers, and yields are significantly higher than planting back over last year's row where higher nematode populations exist. Another concern is that cotton stalks that were mowed off from the previous cotton crop can puncture tires if planted in row middles the following year. This problem can be overcome by mowing stalks higher so that stalks will be pushed over as the tractor tire runs over them.
Comparative reniform nematode population densities in cotton planted in the row or between rows of a previous cotton crop, Test 1.
Initial populations of reniform nematodes and lint yield of cotton planted in-row and in row middles of a previous cotton crop, Test 2.
Comparative reniform nematode population densities in cotton planted in-row and in row middles of a previous cotton crop.