EFFECTS OF SPRINKLER IRRIGATION ON SOIL PHYSICAL PROPERTIES AND GREEN GRAM CROP YIELD

Abstract

Kenya’s land area is 582,646 Km2 with 17% suitable for rain-fed agriculture and 83 % classified as arid and semi-arid and cannot reliably support agricultural activities unless under irrigation . Insufficient water resources make the selection of an efficient irrigation system essential. Sprinkler irrigation is one such tool and despite having been proven to be economical and efficient is known to cause soil compaction leading to reduction in crop yield. The broad objective of the study was to determine the effect of sprinkler size on soil compaction and subsequently on green gram crop yield. Field trials were carried out at Wei Wei Irrigation Development Project in West Pokot County to determine the impact of sprinkler size on soil physical properties and subsequently on crop yield. Completely randomized block design was used as a framework for carrying out the trials. Three different sprinkler size treatments (Jalpari, Taiwan and Naan sprinkler types) with two replications each in six experimental trial plots were tested under subsoiled plots (B, D and F) and non subsoiled plots (A, C and F). Green gram crop was planted under four irrigation schedules of 5 hours each per sprinkler type to harvest. Soil analysis, penetration resistance, sprinkler characteristics, infiltration rates for the different trial plots, irrigation water runoff and soil erosion were determined. The experimental trials plots soils were sandy loam with an average soil bulk density of 1.6 g/cm3 and an optimum compaction moisture content of 17.53%. This soil can easily be compacted and suitable moisture range for land preparation with minimal compaction was determined to be 15.3-17.53% by Proctor compaction test. The soil’s penetration resistance was highest for non subsoiled plots at a depth of 0-20 cm compared with subsoiled plots by 38 bars. The penetration resistance values were between 144 and 160 bars against recommended values of 10-20.68 for crop production. These values were high and indicate that the soil was prone to compaction. Soil compaction was high for Jalpari Sprinkler type (146 bars) with more discharge at the end of experiment compared to Taiwan (142.5 bars) and Naan (145 bars) which had less. Jalpari sprinkler type caused runoff of 0.17 mm/ per irrigation schedule, soil erosion of 0.27 tons/ha/year against RUSLE modeled value of 0.35 tons/ha/year. The difference between the two values was associated with estimated RUSLE parameters which were derived from the experimental project’s region’s existing data. Plots with Taiwan sprinkler having a water application rate of 8.5 mm/hr, DU of 75.88% and CU of 83.2% produced the highest yield with a positive net income of Kshs 80,421.40 per hectare in a subsoiled plot. However yield differences due to sprinkler type were not significantly different. Statistical analysis on yield and tillage type showed similar trend except in yield per plant which had an F-ratio value of 26.1 against the table’s value of 18.51. It could be concluded that sprinklers with high discharge cause compaction, runoff, soil erosion and lower yield. It was recommended that tillage be carried out at soil moisture content range of 15.3-17.53% with an effort of 600 KN-m/m3 or less since this did not create compaction. Taiwan sprinkler and sub soiling which gave the best yields were recommended. Further research on soils, sprinkler types and machinery were also recommended.