tion and K retention by soil constituents in surface layers of no-till soils often are reduced compared with conven-Early plant growth and grain yield of no-till corn (Zea mays L.) tionally tilled soils (Karathanasis and Wells, 1990; Guerare usually lower than for conventionally tilled corn in the northern U.S. Corn Belt. Root-zone fertilization is likely to enhance early tal et al., 1991). Accumulation of P and K near the soil growth and increase yields. This study evaluated the effects of P and surface and reduced retention of these nutrients by soil K placement on early growth and P and K uptake of no-till corn, and constituents result in increased availability of these nuon relationships between these effects and grain yield response to trients in this zone; however, this increased availability placement. Ten long-term P and K trials (5 trials each, P and K) were may not translate into increased nutrient uptake by established in 1994 at five research centers and were evaluated for crops if it is coupled with reduced P and K availability 3 yr; 11 1-yr P-K trials were established in farmers' fields (1994-1996). of deeper layers, because of the likelihood of dry condi-Treatments several P and K rates (0-56 kg P ha Ϫ1 ; 0-132 kg K ha Ϫ1) tions near the soil surface during summer. Residue covbanded with the planter 5 cm beside and below the seeds and broadcast erage may also influence P and K availability. Increased or deep-banded at a 13-to 18-cm depth before planting. Soil samples residue coverage increases water infiltration and soil were collected before applying the treatments from the 0-to 7.5-cm and 7.5-to 15-cm depths. Soil-test P (0-15 cm) ranged from very low moisture but reduces soil temperature at shallow depths to very high across sites and soil-test K ranged from optimum to very (Kaspar et al., 1990). These effects can inhibit plant high. Banded P (deep or shallow) increased early growth and P uptake growth and nutrient availability early in the season, but more than the broadcast placement did at most trials. Phosphorus are likely to increase the activity of shallow roots during increased yields only in very low and low testing soils, and there was dry and warm periods (Barber, 1971). no response to P placement. Banded K (deep or shallow) seldom Several reports have shown that small fertilizer appliaffected early growth, but usually increased K uptake. Potassium cations with the seeds or shallow subsurface banding increased yields in several soils that tested optimum or higher in soilnear the seeds often, but not always, increase yields or test K, and yields were higher when K was deep banded. Planting nutrient uptake of no-till corn compared with broadcast onto a fall-applied coulter-knife track without applying P or K often fertilization (Singh et al., 1966; Belcher and Ragland, increased early growth and nutrient uptake, but seldom increased yields. Early growth and nutrient uptake responses to banded P did 1972; Moschler and Martens, 1975; Eckert and Johnson, not translate into higher yields. Sm...

propriate soil sampling techniques (e.g., in terms of sampling depth and location relative to crop rows or Proper P and K management for no-till crops is uncertain. Potential fertilizer bands), and inefficient fertilizer placement. problems include inappropriate extrapolation of soil test interpretations and fertilizer recommendations from conventional tillage, inap-These problems could arise because of changes in nutripropriate soil sampling techniques, and inefficient fertilizer placement. ent availability at different soil depths, soil temperature This study compared broadcast, deep-band, and planter-band P and and water relations, and root growth and distribution, K placements for no-till corn (Zea mays L.). Long-term P and K among other factors. trials were established in 1994 at five Iowa research centers and were No-till management usually leads to P and K stratifievaluated for 3 yr. Eleven short-term P-K trials were established in cation in soils. Both nutrients accumulate in the soil farmers' fields during the same period. Treatments were various P surface as a result of minimal mixing of surface-applied (0 to 56 kg P ha Ϫ1 ) and K (0 to 132 kg K ha Ϫ1 ) rates broadcast, banded fertilizers and crop residues with soil, limited vertical with the planter 5 cm beside and below the seeds, and deep-banded movement of P and K in most soils, and cycling of at the 15-to 20-cm depth before planting. Soil samples were collected nutrients from deep soil layers to shallow layers through from the 0-to 7.5-cm and 7.5-to 15-cm depths prior to planting. Soiltest P (P ST ) at the 0-to 15-cm depth ranged from very low to very nutrient uptake by roots (Shear and Moschler, 1969;high across sites; soil-test K (K ST ) ranged from optimum to very high. Griffith et al., 1977;Ketchenson, 1980;Mackay et al., There were grain yield responses to fertilization at several sites, but 1987; Karathanasis and Wells, 1990;Karlen et al., 1991). no significant differences between the P or K rates and no interactionsFurthermore, reduced P sorption and K retention by between rates and placements. Phosphorus increased yields only in soil constituents in surface layers of no-till soils (Karasoils testing very low or low, and there was no response to P placement thanasis and Wells, 1990; Guertal et al., 1991) may conat any site. Potassium increased yields in several soils that tested tribute to higher soil test values in this zone. A relative optimum or higher in K ST , and yields were higher when K was deepaccumulation of P and K near the soil surface may banded. High rates of broadcast or planter-banded K did not offset decrease nutrient availability to plants because of the the advantage of deep-banded K. Responses were better related with increased likelihood of dry conditions in this zone. High deficient rainfall in late spring and early summer than with K ST . Current soil-test P interpretations and P fertilizer recommendations based J.M. Bordoli, Fac. de Agronomía, Univ. de la Repú blica, Av. Garzó n attributed to P (Randall and Hoeft,

The recent changes in the agriculture in Uruguay, by the adoption of no-tillage planting systems, have included the use of marginal soils for crop production, being the soybean the main crop that allowed those changes. Several questions have arisen about the sustainability of the intensive soil use of these new production systems. The objective of this work was to detect situations with greater probability of nutrient defi ciencies, using soybean as indicator crop. During crop seasons 2009/10 and 2010/11 a nutritional soil survey of soybean crops was conducted, collecting soil and leaf samples of 178 commercial fi elds widely distributed around the country, at the R1-R2 soybean growth stage. In half of the sites soybean was the main crop, and in the other half soybean was planted following winter crops. Soybean yield ranged from 511 to 5435 kg ha -1 . In 34% of the fi elds pH was below 5.3, even in the traditional agricultural zone. In 54% of fi elds available P was below 12 mg kg -1 of P Bray-1, and 23% of the cases were below 0.30 cmol c kg -1 of exchangeable K. The concentrations of macronutrients in leaves for all the samples were: 3.88 (±0.66) % N; 0.26 (± 0.08) % P; 2.03 (±0.53) % K; 1.14 (±0.23) % Ca; 0.36 (±0.10) % Mg; and 0.29 (±0.07) % S. The micronutrient concentration means were 9, 77, 61, and 30 mg kg -1 of Cu, Fe, Mn, and Zn, respectively. The more frequently defi cient nutrients were P, K, and N, with 42, 39, and 13% of the fi elds with concentrations in leaves below the critical concentrations. The results show that the actual soybean productivity could be partially affected by nutrient defi ciencies, suggesting that soil pH, and P or K corrections need to be considered in the nutritional management program for each crop production system.

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