Abstract
South Texas is located in a subtropical semiarid climate, and due to high temperature and irregular precipitation, farmers opt to leave their fields fallow during the summer months jeopardizing overall soil health. We evaluated whether sweet potato (Ipomoea batatas) cultivation coupled with drip irrigation could restore soil biological activities compared with bare fallow. Additionally, because sweet potatoes have high demand of soil nutrients, especially potassium (K), we evaluated the nutrient supply of locally sourced soil amendments. Sweet potato was cultivated during summer 2018 in McAllen, Texas, under control (no fertilizer), NPK (synthetic fertilizer), RC (yard-waste compost), and AC (compost produced under an enhanced composting process), and biochar (gasified walnut shell at 900°C), each with three replicates. Soil amendments were applied at different amounts to result in a rate of 80 kg K ha−1. Soil biological indicators were microbial biomass phosphorous, phosphatase activity, and the rate of fluorescein diacetate hydrolysis (FDA). Available nitrogen, phosphorus, potassium, and sodium were also quantified. Aboveground biomass and storage root yield estimated sweet potato’s agronomic performance. Cultivation and irrigation stimulated soil enzyme activities and microbial biomass-phosphorous. Sweet potato yields were the highest in NPK treatment but still 2.8 times lower than variety’s potential yield. Storage root yield was inversely related to aboveground biomass, suggesting that growing conditions benefited the production of shoot versus roots. Both biochar and AC treatments stimulated FDA rates and K availability. Soil pH and sodium concentration increased in all treatments over the growing season, possibly due to river-sourced irrigation water. Together, these findings show that crop cultivation promoted soil biological activities and the maintenance of nutrient cycling, compared to bare-fallow conditions. For a better agronomic performance of sweet potato, it would be necessary to identify management practices that minimize increase in soil pH and salinity.
Highlights
In the South Texas region of the Lower Rio Grande Valley on the border with Mexico is a well-established and diverse agricultural expanse, boasting citrus, cotton, sugar cane, onions, and leafy vegetables
The storage root yield was inversely related to aboveground biomass (Table 2; r2 −0.54, p < 0.001)
In South Texas, in the Lower Rio Grande Valley, soils are characterized as nutrient poor soils, as shown by its low percentage of nitrogen and carbon and high alkalinity, limiting the availability of micronutrients such as iron, manganese, copper, cobalt, and zinc
Summary
In the South Texas region of the Lower Rio Grande Valley on the border with Mexico is a well-established and diverse agricultural expanse, boasting citrus, cotton, sugar cane, onions, and leafy vegetables. Under a subtropical semiarid climate, the average temperature in South Texas throughout the summer is 35°C, presenting extreme drought and flooding periods with increasing intensity and frequency [1]. E average annual rainfall is 430 to 685 mm with irregular distribution throughout the year, making the agricultural industry highly dependent on irrigation water [2]. E soils suffer from salinity issues deposited by irrigation water from the Rio Grande that. The typically high temperatures promote water loss via evaporation increasing the accumulation of salts in the soil [4]. Given the high temperatures and water challenges, vegetable farmers leave the land bare fallow throughout the summer, as crops are often damaged by extreme heat, and high irrigation costs make production impracticable
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