Hail influence on corn (Zea mays L.) yield depends on defoliation timing and severity. Complete defoliation during early vegetative stages can have minimum yield effects if plants’ growing point is not affected but can generate some delays in the planting to flowering period. Low‐severity defoliations after V10 can reduce yield up to 30%. Higher severities gradually increase yield penalties to a peak around flowering and decrease progressively during the grain‐filling period. Charts to estimate the percentage of corn yield loss due to defoliation developed in the late 1960s are still accurate in most situations but fail to describe particular situations. Defoliation around VT commonly affects time to silking, anthesis–silking interval, and plant growth rate, but not time to anthesis, and is commonly explained by lower kernel number (KN). Defoliation at R2 commonly affects kernel weight (KW), without changing KN. However, several studies showed a reduction in both KW and KN with R2 defoliations. Under low plant disease pressure, fungicides applied around VT do not help reduce any yield defoliation impact. Specific genotypes, row spacing, and hybrid maturity can influence crop yield defoliation responses. More studies are warranted to confirm the potential for narrow rows to reduce yield loss after defoliation.

Planting cover crops after corn-silage harvest could have a critical role in the recovery of residual N and N from fall-applied manure, which would otherwise be lost to the environment. Experiments were conducted at the University of Massachusetts Research Farm during the 2004-2006 growing seasons. Treatments consisted of oat and winter rye cover crops, and no cover crop, and four cover-crop dates of planting. The earliest planting dates of oat and winter rye produced the maximum biomass yield and resulted in the highest nitrate accumulation in both cover-crop species. The average nitrate accumulation for the 3 years in winter rye and oat at the earliest time of planting was 60 and 48 kg ha -1 , respectively. In 2004 where the residual N level was high, winter rye accumulated 119 kg nitrate ha -1 . While initially soil N levels were relatively high in early September they were almost zero at all sampling depths in all plots with and without cover crops later in the fall before the ground was frozen. However, in plots with cover crops, nitrate was accumulated in the cover-crop tissue, whereas in plots with no cover crop the nitrate was lost to the environment mainly through leaching. The seeding date of cover crops influenced the contribution of N available to the subsequent crop. Corn plants with no added fertilizer, yielded 41% and 34% more silage when planted after oat and rye, respectively, compared with the no-cover crop treatment. Corn-silage yield decreased linearly when planting of cover crops was delayed from early September to early or mid-October. Corn-ear yield was influenced more than silage by the species of cover crop and planting date. Similar to corn silage, ear yield was higher when corn was planted after oat. This could be attributed in part to the winter-kill of oat, giving it more time to decompose in the soil and subsequent greater release of N, while the rapidly increasing C : N ratio of rye can lessen availability to corn plants. Early plantings of cover crops increased corn-ear yield up to 59% compared with corn-ear yield planted after no cover crop.

Animal manure is typically applied to meet the N needs of crops. This can lead to overapplication of P and K. We evaluated the impact of a change from N‐based applications of manure and compost without incorporation to a P‐based (crop‐removal) management system with immediate incorporation of manure on (i) silage corn (Zea mays L.) yield and quality, and (ii) soil test NO3, P (STP), and K (STK). A 5‐yr field study was conducted with annual spring applications of composted dairy solids (46 and 74 Mg ha−1), liquid dairy manure (68 and 196 kL ha−1), and inorganic N fertilizer (0 and 112 kg ha−1). Shifting from N‐ to P‐based manure and compost management reduced the corn yield by 7 to 13% and protein by 8 to 9%, suggesting that fertilizer N is needed for P‐based management. Shifting from N‐ to P‐based manure management reduced soil NO3–N at silage harvest by 39% vs. 21% for compost. After 5 yr, STP increased four‐ and sixfold and two‐ and fourfold for N‐ and P‐based manure and compost management, respectively, reflecting positive P balances (lower than anticipated yields). Soil test K increased three‐ and twofold with N‐ and P‐based manure and compost management, respectively. Both STP and STK remained unchanged with inorganic N fertilization. We conclude that a shift from N‐ to P‐based compost and manure management, with immediate incorporation of manure, leads to reduced soil P and K buildup and, for manure, also soil NO3, but supplemental inorganic N fertilization is required to ensure that crop N needs are met.

No abstract

No abstract