Date of Award:

5-2019

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Advisor/Chair:

Grant E. Cardon

Co-Advisor/Chair:

J. Earl Creech

Third Advisor:

Paul R. Grossl

Abstract

Soluble phosphorus fertilizer is bound in the soil rapidly after application in soils high in calcium. A fertilizer additive known as AVAIL® (J.R. Simplot Company) is purported to keep applied phosphorus fertilizer more available to plants by binding to soil minerals such as calcium, magnesium, and iron, thereby reducing phosphorus binding. This could prove useful due to the attraction of AVAIL® with cations such as Ca2+, but is fairly unstudied for dryland wheat production on alkaline, calcium-rich soils. The objective of this study is to evaluate the effect of low-rate fertilizer treatments with AVAIL® on dryland small grain yield on calcium-rich, eroded hillslopes in a fallow-wheat crop rotation. Two experiments were conducted to determine treatment effects on yield and grain quality for (1) above-ground dispersed (broadcast) application of monoammonium phosphate (MAP; 52% P2O5 content) fertilizer in the spring (2017), and (2) fall application of MAP incorporated with the seed (banded) at planting (2018). Fertilizer treatments were the recommended rate (60 lbs/ac) or one-half the recommended rate (30 lbs/ac) for dryland small grain, with or without AVAIL® (four treatments), replicated four times in a strip-block design for the 2017 experiment and replicated 3 times in a randomized complete block design for the 2018 experiment. Experimental blocks were assigned to hillslope erosional severity groups. The erosional severity groups were v designated (non-eroded, slightly eroded, highly eroded, and depositional slope segments). Hillslope segmentation allowed for correlations between calcium carbonate, organic matter, and yield levels across treatments. Results from the broadcast study indicate that there was no yield advantage of any treatment at any level of erosional severity, saving a grower $20.30/acre by applying 30 lbs/acre of MAP. However, 30 lbs/acre of MAP with AVAIL® showed similar yield to 60 lbs/acre of MAP without AVAIL®, potentially saving a grower $6.42/acre over standard growing practices. The incorporated study also indicated that there was no reliable yield advantage of any fertilizer treatment at any level of erosional severity, saving a grower $15.37/acre by applying 30 lbs/acre of MAP. Neither treatment with AVAIL had greater yield or profit than those without AVAIL. Profit for the 60 lbs/acre of MAP treatment narrowly outperformed 30 lbs/acre of MAP by $1.73/acre, indicating that growers may be able to reduce phosphorus use under dryland growing conditions with optimal fertilizer placement.

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