A Subsurface Irrigated, Controlled Traffic, No- Tillage System

Abstract

A subsurface trickle irrigation system was protected from damage for 21 months through use of a controlled traffic pattern and no-till agriculture. During this period, seven successive vegetable crops were grown without disturbing the irrigation system. Subsequent inspection of the system indicated that this combination of techniques would enable it to operate for periods greater than two years at acceptable levels without replacement. The experiment was conducted on two soils, a light volcanic ash soil and a heavy alluvial soil with less favorable physical properties, to assess the general applicability of the results. Natural soil compaction over a 16-month period showed no significant effect on yields. Severe compaction imposed by tractor traffic resulted in a decrease in lettuce root weight of one-half, yet it had no significant effect on crop yield. Emitter plugging increased from an average of 23% in the non-compacted plots to 36% in the compacted plots with similar results in both shallow and deep (13 and 28 cm) lateral line placement. Plugging did not significantly reduce crop yields. Water movement along the trickle line and the intermittent nature of plugging may have reduced the influence of plugging on lettuce yields. The results from these experiments indicate that for shallow-rooted, short duration, transplanted vegetable crops, such as lettuce and cabbage, acceptable yields can be obtained without extensive tillage if water and nutrients are adequately supplied. Phosphorus fertilizer distributed through the trickle system was immobilized within 10 cm or less of the emitters. Because transplanted seedlings were placed directly over the emitters, this "banding" effect was more efficient than broadcast applications at similar rates in supplying nutrients to the first crop of lettuce. The results of this research suggest that economy in time and expense may be achieved with a no-till, controlled traffic, subsurface trickle irrigation system. This method permits vegetable growers and others to exploit the benefits of reduced tillage, optimum soil-water conditions, and distribution of fertilizers through the irrigation system. In addition, phosphorus use efficiency may be increased by transplanting over the emitters. With this approach, growers can minimize the cost of lateral line repair and eliminate the cost of removing or replacing trickle laterals for each harvest cycle.