Identification and Diagnosis of Long-Term Problem Areas in Fields of Agronomic Crops

Since farming began, those who tilled the soil and planted and harvested crops have noticed areas within boundaries of their fields that do not produce as well as other areas. Centuries ago, nomadic farmers attributed these events to the wrath of unhappy gods or witches’ curses. However, with today’s technologies farmers can do better. Farmers today must also produce more to meet the food demands of a growing world population. To maintain their competitive advantage, American farmers need to be producing crops more efficiently than other producers in the world’s agricultural commodity markets. The objective of this paper is to educate producers to recognize what they need to test for and how to evaluating test results when dealing with problem areas in fields. Two different problem areas within two different soybean (Glycine max) fields were observed, analyzed, and tested in Caroline County during the 2017 growing season. Farmers verified that problem areas existed for years, and so in both fields, both problem areas as well as adjacent non-problem areas were tested for soil fertility, soybean nutrient content, and nematodes. Comparative tests confirmed that the problematic areas in both fields had inadequate fertility and low pH, and detrimental population levels of nematodes, which were exacerbated by low pH and inadequate fertility. Nematode species varied by site but included root knot (Meloidogyne spp.), dagger (Xiphinema spp.), and sting (Belonolaimus spp.) nematodes. The comparative tests also confirmed that of the two problem spots, the problem spots in both fields were the same soil series as the remainder of the field. Site A’s problem area had a low pH, low potassium, and 1660 root knot nematodes per 500 mg of soil. A root knot population over 170 is detrimental to a soybean. Other diseases found included charcoal rot (Macrophomina phaseolina) and fusarium root rot and wilt (Fusarium spp). Soybeans in the problem area in Site A were 50% shorter than the rest of the field and contained few pods at the R6 growth stage. Site B’s problem area soybean stand was 50% shorter than the rest of the field and also had considerably fewer pods. Site A’s problem area also suffered from a low pH, and phosphorus was yield limiting from both low pH and low soil levels. Site B also had detrimental levels of nematodes, with 160 sting nematodes and 440 dagger nematodes, in addition to fall panicum (Panicum dichotomiflorum) and large crabgrass (Digitaria sanguinalis). In conclusion, problem spots in fields present a problem for farmers in Virginia that need evaluating, and when evaluating, all factors such as soil fertility, environmental aspects, pests, and genetic potential should be considered.